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Your RMV Rate, How To Calculate And Use It To Be A Better Diver!

By Jose Cernuda

How much gas did you have left after your last dive? Do you know the precise number as a volume? Do you know how much your average consumption rate is? While It’s extremely common for divers to ask each other how much gas they had left after a dive many people express what was left in terms of PSI or BAR. And while that’s helpful if both you and your buddy were using the same tank it becomes tricky if you’re using different cylinders.

The most precise way to know is using your RMV. If you are serious about diving and improving your diving then you need to know this number. There is a famous business quote from Peter Drucker “If you can’t measure it, you can’t manage it”. This is certainly true of your breathing rate. If you’ve ever wondered about how to measure, use and calculate your breathing rate you’re going to want to read on.

What is RMV?

RMV stands for Respiratory Minute Volume. It is a way divers express how much gas was consumed during a dive. RMV is always expressed as a volume. In the Imperial system, we use cubic feet per minute to express RMV. In the Metric system, RMV is expressed in Liters per minute. RMV is usually standardized as a measurement on the surface. This means that if, for example, you have an RMV of 1 cubic foot per minute  (28 liters per minute) on the surface you’ll use 2 cubic feet (56 liters) at 33 feet (10 meters), 3 cubic feet (84 liters) at 66 feet (20 meters), etc.. because of Boyles Law and the increase in atmospheric pressure. The illustration below shows how the increase in depth/pressure also affects your breathing rate.

By knowing the amount of gas you consume on a dive you will know:

  • If you consumed more or less than on your average dive
  • If your breathing rate is getting better or worse
  • How much gas you need to do a particular dive
  • What tank capacity is best suited for you

RMV Vs. SAC

SAC stands for Surface Air Consumption (rate). Many divers use the terms RMV and SAC interchangeably. Strictly speaking, however, SAC is supposed to be measured in PSI per minute or BAR per minute. Because it is a measurement of pressure, SAC is specific to the tank that it was measured on. This means your SAC rate will be different when you use a different-sized tank. We did a separate article on SAC rates here if you are interested in delving into this topic.

The important thing to understand is that If you look at the online calculators, apps that are available for smartphones, and even the software used for dive computers you’ll see that it’s difficult to get a consensus on whether SAC should always be measured as a pressure or a volume. RMV however, is always measured as a volume. For this reason, RMV is the unit of measurement I like to use when teaching how to measure your breathing rate. If you are unsure, just keep reading on. RMV is probably the better choice.

Ultimately, It doesn’t matter if you measure your breathing rate as cubic feet per minute, liters per minute, BAR per minute, or PSI per minute as long as you understand what you are measuring and how to use your measurements. There are many online debates about this very topic, but for our purposes, we’ll treat RMV as a volume and SAC as a measurement of pressure.

RMV Calculator

Now that you understand what RMV is, let’s look at what you need to measure to figure out your surface Respiratory Minute Volume. Because the information you need is slightly different in the imperial system than it is in the metric system, we’ll go over both below.

Imperial System

To figure out your RMV you’ll need to know the capacity of the tank you used for a given dive as well as its service pressure. You’ll then go on a dive and for a minimum of 10 minutes (longer is better) and make a note of your average depth, your starting and ending pressure in PSI during your timed RMV test and the amount of time you ran your test for. We’ll give you tips later in this article on best practices for getting these numbers, but for now, you just need to know the information you’ll need to collect. With these numbers on hand, you can plug them into the calculator below to get your surface RMV.

RMV Calculator (Imperial)

Metric System

To figure out your RMV in the metric system you’ll need to know the capacity of the tank you used for a given dive. Then you’ll then go on a dive and for a minimum of 10 minutes (longer is better) and make a take note of your average depth, your starting and ending pressure in BAR during your timed RMV test, and the amount of time you ran your test for. We’ll give you tips later in this article on best practices for getting these numbers, but for now, you just need to know the information you’ll need to collect. With these numbers on hand, you can plug them into the calculator below to get your surface RMV.

RMV Calculator (Metric)

Best Practices for Measuring Your RMV

To get the most accurate RMV possible you’ll want to follow the following 3 tips”

  • Pick a dive where you won’t be exerting yourself excessively because of currents or any other conditions.
  • Use a slate to write down all your information
  • Pick a dive where your depth will be relatively constant.

With your slate ready, and calm dive where you’ll maintain a relatively constant depth you’ll be ready to begin your RMV test.

Once you’ve descended and ready to begin measuring, you’ll take a look at your submersible pressure gauge (SPG) and write down your pressure in PSI or BAR. You’ll also want to make a note of the time. Then simply go about your dive as usual. You’ll want to measure for at least 10 minutes (the longer the better). After 10 or more minutes have elapsed make a note of how much gas is left as measured by your SPG and also how long you were diving for. You’ll also need to make a note of average depth during the test. With these numbers handy you can now calculate your RMV either manually or using the online RMV calculator.

What is a good RMV?

A lot of factors go into determining your RMV rate. The single biggest factor is probably your body size. Below is a chart with average RMV rates for an experienced diver using an Aluminum 80 (11.2 liter) tank. This is for a dive where the diver is not exerting themselves and in tropical waters. It is only a guide to get a rough idea of where your RMV could be. You may be higher or lower than what’s listed on the table.

  • Imperial

  • Metric

Under 140140-180180-220220 Plus
0.4 Cu. Ft. per minute0.5 Cu. Ft. per minute0.6 Cu. Ft. per minute0.7 Cu. Ft. per minute

What Affects your RMV Rate?

Many factors influence the rate at which you consume gas from your SCUBA tank. Some of those factors include:

  • Your physical size: The larger you are the larger your lungs are and the more gas you will consume as you dive.
  • Your exertion level throughout the dive: Swimming fast or against a current are examples of things that will cause you to use more gas.
  • Your buoyancy and trim throughout the dive: If your buoyancy is off or you’re not properly trimmed out in the water, you will likely exert yourself more and consume more gas throughout the dive.
  • Water Temperature: If you do not have proper thermal protection, your body may begin to shiver and you’ll consume more gas as a consequence of your body trying to stay warm.
  • Mental State / Anxiety: If you are anxious, nervous, or not confident in your diving ability this increased anxiousness will often cause you to breathe faster
  • Your level of physical fitness: The more cardiovascularly fit you are the more efficient your breathing will be. If you become winded from climbing a flight of stairs, you’ll also likely consume more gas while diving than someone who regularly runs marathons.

How Can I Decrease My SAC Rate?

A good RMV rate is part of being a great diver! There are many things you can do to improve your RMV rate. Many of these suggestions are topics on to themselves and we even have an entire course, much of which is devoted to helping you achieve a lower RMV rate. Below are the top 4 things you can do to decrease your RMV rate.

Master your Buoyancy

If you are struggling to stay down because you don’t have enough ballast or have too much ballast and are kicking just to stay off the bottom, then you are surely wasting energy and driving your RMV rate up. Doing a proper buoyancy check, learning where your dump valves are, and mastering buoyancy are the first steps toward a lower RMV rate.

Learn How to Trim Your Body Out properly. 

If you are not trimmed out properly in the water, you’ll consume more energy throughout the dive. Notice in the illustration below how the diver to the left encounters more resistance as she tries to kick. This is because she isn’t trimmed out efficiently.

Use the Frog Kick or the Modified Frog Kick More

The frog kick and the modified frog kick require less energy than the flutter kick when you are diving. Because these kicks have a resting phase built-in you end up kicking less to cover the same distance underwater. Mastering the frog kick and the modified frog kick is one of the things you can do to help to lower your breathing rate.

Become Comfortable Underwater

Your mental state plays a larger role in your breathing rate than most people realize. If you are not completely comfortable underwater it’s likely that your heightened state of anxiety will also raise your breathing rate. Being comfortable with all the basics of SCUBA diving including mask removal and replacement and buddy breathing, in case of emergency, are just the beginning.

Using Your RMV to Estimate the Gas Needed For A Dive

Once you know what your RMV, you can use it to estimate the amount of gas you’ll need at depth. Remember that in salt water you’ll encounter an additional atmosphere of pressure every 33 feet (10 meters. Because of this, the deeper you go the more gas you’ll consume. You can use the calculator below to estimate how much gas you’ll need at a given depth and time.

  • Imperial

  • Metric

Using Your RMV To Choose A SCUBA Cylinder

Similar to estimating the gas you’ll need for a dive you can also use your RMV to help you choose the best SCUBA tank for given dive. There are a couple of things you need to keep in mind when doing this. First, remember that you always need to leave an amount of gas in the tank for emergencies. You never want to completely drain a SCUBA tank. Second, if you are purchasing a tank, you want to purchase one that you can use for the deepest dives you plan to do.

With this in mind, you can look at a dive table to determine what the no-decompression limit is for the depth you plan to dive to. From here, knowing your RMV you can determine the amount of gas you’d need to complete the dive. Add in your reserve gas and you should have a good idea of the capacity of the tank that you need. There’s a bit more to choosing a tank, but at least you have an idea of the capacity of the cylinder you should get. For more information on choosing the best SCUBA tank for you check out this article.

Calculating Your RMV Manually

Imperial System

To manually calculate your RMV you’ll need to know the capacity and working pressure of the cylinder you used during your RMV test. You’ll also need to know your starting PSI, your ending PSI, your average depth, and the time you did the test for.

Step 1: Calculate your “Tank Factor”. The “Tank Factor” is a name given to the value in cubic feet that 1 PSI represents. Calculating your tank factor is simple. Just divide the capacity of the tank by its service pressure. So, as an example, if you are using aluminum 80 for the test. You can look at the tank's specifications (LINK) and determine that an aluminum 80 has 77.4 cubic feet when filled to 3000 PSI. That means that the tank factor is (77.4 / 3000) = .0258.

Step 2: Determine how much gas was used during the test in cubic feet. Let’s assume during your RMV test you started with 2700 PSI and ended the test with 1900 PSI. This means you consumed 800 PSI during the test (2700 PSI – 1900 PSI) = 800 PSI. You need to convert 800 PSI to cubic feet, so now you’ll multiply the PSI consumed by the tank factor found in step 1. So (800 * .0258) = 20.64 Cubic Feet.

Step 3: Calculate your depth in Atmospheres Absolute. RMV is expressed at the surface. This means you need to account for the atmospheric pressure and how it compresses the gas you breathe underwater. Let’s assume you did your test at an average depth of 50 feet. To convert 50 feet to ATA you’ll divide it by 33 and then add 1. This is assuming your dive was in saltwater. For freshwater, you would divide by 34 and add 1. This is because salt water is slightly denser than freshwater. So ((50/33)+1) = 2.515 Atmospheres absolute.

Step 4: Divide the total gas in cubic feet by your ATA. So (20.64 / 2.515) = 8.2 Cubic Feet.

Step 5: Divide your result from step 4 by the total amount of time the test was conducted for. Let’s assume we ran our test for 15 minutes. This means (8.2 / 15) = .547.

For this test, the average RMV is .547. We can round this up to .55. This means the diver breathes about .55 cubic feet each minute on the surface.

Metric System

To manually calculate your RMV you’ll need to know the capacity of the cylinder you used during your RMV test. You’ll also need to know your starting BAR, your ending BAR, your average depth, and the time you did the test for.

Step 1: Determine how much gas was used during the test in Liters. Let’s assume you completed your RMV test with an 11.1-liter tank. During your RMV test, you started with 180 BAR and ended the test with 110 BAR. This means you consumed 70 BAR during the test (180 BAR – 110 BAR) = 70 BAR. You need to convert 70 BAR to liters, so now you’ll multiply the BAR consumed by the capacity of the cylinder. So (11.1 * 60) = 777. This means you consumed 777 liters of gas during the test

Step 2: Calculate your depth in Atmospheres Absolute. RMV is expressed at the surface. This means you need to account for the atmospheric pressure and how it compresses the gas you breathe underwater. Let’s assume you did your test at an average depth of 15 meters. To convert 15 meters to ATA you’ll divide it by 10 and then add 1. So ((15/10)+1) = 2.5 Atmospheres absolute.

Step 3: Divide the total gas in liters by your ATA. So (777 / 2.5) = 310.8 liters. This is the amount of gas you consumed when adjusted for atmospheric pressure.

Step 4: Divide your result from step 3 by the total amount of time the test was conducted for. Let’s assume we ran our test for 20 minutes. This means (310.8 / 20) = 15.54.

For this test, the average RMV is .15.54 liters per minute. We can round this up to 15.5. This means the diver breathes about 15.5 liters each minute on the surface.

Knowing your RMV rate, how to calculate it and how to use it is one of the most powerful tools you can have in your diving arsenal. What’s your RMV rate and how do you use it? Let us know in the comments below.

Your SAC Rate, Why It’s Important, and Why You Need To Know How To Calculate It!

By Jose Cernuda

One of the main things that separate experienced and efficient divers from novices is the amount of gas they consume during a dive. Efficient divers will use less gas than someone new and still learning to SCUBA dive. It’s not uncommon as a beginning diver to come back to the boat with just your reserve pressure while your instructor still has their tank half full.  So, how can you measure the amount of gas being consumed by a diver? This is where your SAC rate comes in.

What is SAC Rate?

Surface Air Consumption (SAC) rate is a measurement used to express how much gas a diver uses while diving. In the imperial system, it is measured in pounds per square inch (PSI) per minute. In the metric system, we measure surface air consumption in BAR per minute. It’s extremely important to understand that the measurement is expressed at the surface. Because atmospheric pressure increases as we dive deeper, the deeper we go, the more gas we consume.

This means that a diver who, for example, breathes 30 PSI per minute on the surface will use 60 PSI at 33 feet (10 meters) and 90 PSI at 66 feet (20 meters). As you can see from the image below, the deeper you go the more gas you will consume. 

SAC Rate Calculator

To figure out your SAC rate you’ll need your average depth for a dive, the time you dived for, the amount of gas you observed was used on your submersible pressure gauge (SPG) in PSI or BAR, and the tank you are using during the dive. 

Below is a SAC rate calculator. To understand how the math behind how the SAC rate is calculated, the best practices for getting these numbers, and how you can use your SAC rate read on.

  • Imperial

  • Metric

Why is SAC Rate Important? 

Knowing your SAC rate is important for several reasons, you can use it to:

  • Estimate how much gas will be needed for a given dive
  • Choose the correct sized tank for a dive
  • Track your progress as a diver to see how you improve from dive to dive
  • In Technical diving use it to calculate the amount of gas needed for decompression and in case of emergencies

Dive Computers and your SAC Rate

You can calculate your SAC rate manually, by using a calculator like the one on this page, or you can also get your SAC rate from many dive computers. If your dive computer is air integrated there is a good chance that your dive computer calculates your SAC rate for you.

Even if your dive computer isn’t air integrated, there’s a chance the app or software that connects to your computer can calculate your SAC rate for you.

Because information about your dives is stored by the dive computer, all you need to do is enter the information about the cylinder you used for the dive, your starting pressure, and your ending pressure to have the software calculate your SAC rate.

An important distinction is that not all dive computers / Instructors / textbooks use the term SAC rate. Some call your breathing rate your Respiratory Minute Volume (RMV) or even Surface Consumption Rate (SCR). All these terms are used universally by divers to measure and keep track of your breathing rate on the surface.

What is RMV in SCUBA Diving? 

Respiratory Minute Volume (RMV) is the amount of gas that a diver consumes during a dive expressed as a volume. The measurement is expressed as on the surface. In the imperial system, we use Cubic Feet per Minute to express our RMV. In The metric system, we use Liters Per Minute.

RMV VS. SAC What’s the difference?

In the diving community the terms Surface Air Consumption (SAC) rate and Respiratory Minute Volume (RMV) rate, are often used interchangeably. Even though the difference is that SAC is expressed as PSI per minute (imperial) or BAR per minute (Metric). While RMV is expressed as a volume (cubic feet per minute or liters per minute).

The problem with using the SAC rate in diving is that the number is dependent on the cylinder being used. So, if for example, you go from using an Aluminum 80 on one dive to a low-pressure steel 95 on a different dive, the SAC rate you calculated using the aluminum 80 won’t be accurate now that you switched tanks. When you standardize the number to RMV the number stays the same no matter what tank you dive with.

I personally teach how to calculate RMV in my SCUBA classes and bypass the entire discussion of SAC rate because it’s a universal number that doesn’t change based on the tank you are using.

Because SAC and RMV are used interchangeably by many, you may find SAC calculators both online, inside of apps, and by dive computers that express the breathing rate as a volume (cubic feet per minute or liters per minute). There is much discussion on internet forums about this topic. The important thing is to understand is what the numbers mean and if you are diving with a buddy and you are comparing numbers to make sure you both are using the same unit of measurement. The semantics about whether SAC should be expressed as pressure or as a volume is really irrelevant when you understand the math and how to use it. 

RMV Calculator

Using the RMV calculator below you can see how you get a value that represents volume instead of PSI or BAR. This value is more useful since the volume of gas that you breathe remains constant with different tanks.

  • Imperial

  • Metric

SAC Rate to RMV Calculator

If you already know your SAC rate and the tank you used when you calculated it. You can use the SAC rate to RMV calculator below to convert your SAC rate to RMV. This calculator takes your PSI per minute and converts it to Cubic feet per minute in the imperial system. In the metric calculator it converts BAR per minute to Liters per minute. 

  • Imperial

  • Metric

Best Practices for Measuring Your SAC or RMV

Regardless of whether you use SAC or RMV to measure your breathing rate, the process of measuring it is the same. You’ll want to pick a dive where you won’t be exerting yourself excessively because of currents or any other conditions. You’ll also want to pick a dive where your depth will be relatively constant. Once you’ve descended and ready to begin measuring, you’ll take a look at your submersible pressure gauge (SPG) and write down your pressure in PSI or BAR. You’ll also want to make a note of the time. Then simply go about your dive as usual. You’ll want to measure for at least 10 minutes (the longer the better). After 10 or more minutes have elapsed make a note of how much gas is left as measured by your SPG and also how long you were diving for. You’ll also need to make a note of average depth during the test. With these numbers handy you can now calculate your SAC or RMV either manually or using the online calculator.

Your SAC/RMV at Depth

Once you know what your SAC / RMV is, you can use it to estimate the amount of gas you’ll need at depth. Remember that in saltwater you’ll encounter an additional atmosphere of pressure every 33 feet (10 meters). Using the calculator below you can estimate how much gas you’ll use for a given dive. It's important to understand that the calculator below only calculates how much gas you will consume. You also need to factor in your reserve gas in case of an emergency!

  • Imperial

  • Metric

What Affects your SAC Rate / RMV Rate?

Many factors influence the rate at which you consume gas from your SCUBA tank. Some of those factors include:

  • Your physical size: The larger you are the larger your lungs are and the more gas you will consume as you dive.
  • Your exertion level throughout the dive: Swimming fast or against a current are examples of things that will cause you to use more gas.
  • Your buoyancy and trim throughout the dive: If your buoyancy is off or you’re not properly trimmed out in the water, you will likely exert yourself more and consume more gas throughout the dive.
  • Water Temperature: If you do not have proper thermal protection, your body may begin to shiver and you’ll consume more gas as a consequence of your body trying to stay warm.
  • Mental State / Anxiety: If you are anxious, nervous, or not confident in your diving ability this increased anxiousness will often cause you to breathe faster
  • Your level of physical fitness: The more cardiovascularly fit you are the more efficient your breathing will be. If you become winded from climbing a flight of stairs, you’ll also likely consume more gas while diving than someone who regularly runs marathons.

What Is A Good SAC Rate?

A lot of factors go into determining your SAC rate. The single biggest factor is probably your body size. Below is a chart with average SAC / RMV rates for an experienced diver using an Aluminum 80 (Aluminum 11.2 liter) tank. This is for a dive where the diver is not exerting themselves, in tropical waters using a single tank. It is only a guide to get a rough idea of where your SAC / RMV could be. You may be higher or lower than what’s listed on the table. The important thing is to do the measurement and know your measurement. Once you have a starting point you can work on improving your SAC rate. 

  • Imperial

  • Metric

RMV / SAC Rates by Diver in Pounds

Under 140140-180180-220220 Plus
0.4 Cu. Ft. per minute0.5 Cu. Ft. per minute0.6 Cu. Ft. per minute0.7 Cu. Ft. per minute
16 PSI per minute20 PSI per minute24 PSI per minute28 PSI per minute

How Can I Decrease My SAC Rate?

A good SAC rate is part of being a great diver! There are many things you can do to improve your SAC rate. Many of these suggestions are topics on to themselves and we even have an entire course, much of which is devoted to helping you achieve a lower SAC rate. Below are the top 4 things you can do to decrease your SAC rate.

Master your Buoyancy

If you are struggling to stay down because you don’t have enough ballast or have too much ballast and are kicking just to stay off the bottom, then you are surely wasting energy and driving your SAC rate up. Doing a proper buoyancy check, learning where your dump valves are, and mastering buoyancy are the first steps toward a lower SAC rate.

Learn how to trim your body out properly. 

If you are not trimmed out properly in the water, you’ll consume more energy throughout the dive. Notice in the illustration below how the diver to the left encounters more resistance as she tries to kick. This is because she isn’t trimmed out efficiently.

Use the frog kick or modified frog kick more

The frog kick and the modified frog kick require less energy than the flutter kick when you are diving. Because these kicks have a resting phase built-in you end up kicking less to cover the same distance underwater. Mastering the frog kick and the modified frog kick are one of the things you can do to help to lower your breathing rate.

Become More Comfortable Underwater

Your mental state plays a larger role in your breathing rate than most people realize. If you are not completely comfortable underwater it’s likely that your heightened state of anxiety will also raise your breathing rate. Being comfortable with all the basics of SCUBA diving including mask removal and replacement and buddy breathing, in case of emergency, are just the beginning. As you gain experience and become completely comfortable with being underwater your breathing rate will become lower. 

How To Calculate SAC Rate (Formula)

You might be wondering, how are the numbers given by the calculators computed? Below is the explanation so you can understand the math and how the SAC rate works.

Imperial System SAC Rate Calculation

Computing your SAC rate is fairly straight forward. Remember to follow the guidelines in this article best practices for calculating your SAC / RMV. You can calculate your SAC rate in 3 easy steps. To do so, you’ll need the following:

  • Average depth during the test
  • Starting and ending PSI during the test
  • The amount of time you conducted your SAC rate test for

Let’s assume the following variables for our example:

  • Depth = 55 Feet (Saltwater)
  • Starting PSI = 2700, Ending PSI = 1800
  • Time of Test = 15 minutes

Step 1: Figure out your depth in atmospheres absolute. In this example we assume a dive in saltwater, so we use 33 feet as an atmosphere. If you are diving in freshwater, you’d use 34 feet to calculate an atmosphere. To figure out your depth in atmospheres absolute (ATA) divide your depth by 33 and add 1 to it. So, if for example, you dived to 55 feet, you’ll divide 55 by 33 and add 1. So (55/33) + 1 = 2.68. 2.68 = Your depth in atmospheres absolute (ATA)

Step 2: Figure out how much gas you used in PSI. Assuming you started your test with 2700 PSI and you ended up with 1800 PSI, it means you consumed 900 PSI during your test. 2700 PSI-1800 PSI= 900 PSI.

Step 3: Divide the total PSI used by your ATA and then by the total number of minutes you did the test for. So (900/2.68 = 335.82) and (335.82/15 = 22.38). This gives you your SAC rate. So your SAC rate for this example is 22.38 PSI per minute.

The Formula for calculating your SAC rate is.

((Starting PSI – Ending PSI) / Depth in ATA) / Duration of test) = SAC Rate

*Remember that your SAC rate is dependent on the cylinder you used. Your SAC rate will be different if you use a different cylinder.

Metric System SAC Rate Calculation

Computing your SAC rate is fairly straight forward in the metric system. Remember to follow the guidelines in this article best practices for calculating your SAC / RMV. You can calculate your SAC rate in 3 easy steps. To do so, you’ll need the following:

  • Average depth during the test
  • Starting and ending BAR during the test
  • The amount of time you conducted your SAC rate test for

Let’s assume the following variables for our example:

  • Depth = 17 Meters (Saltwater)
  • Starting pressure in BAR = 190, Ending pressure in BAR = 120
  • Time of Test = 15 minutes

Step 1: Figure out your depth in atmospheres absolute. To figure out your depth in atmospheres absolute (ATA) divide your depth by 17 Meters By 10 and add 1 to it. So, if for example, you dived to 17 meters, you’ll divide 17 by 10 and add 1. So (17/10) + 1 = 2.7. 2.7 = Your depth in atmospheres absolute (ATA)

Step 2: Figure out how much gas you used in PSI. Assuming you started your test with 190 BAR and you ended up with 120 BAR, it means you consumed 70 BAR during your test. 190 BAR -120 BAR = 70 BAR.

Step 3: Divide the total pressure in BAR you used by your ATA and then by the total number of minutes you did the test for. So (70/2.7 = 25.92) and (25.92/15 = 1.72). This gives you your SAC rate. So, your SAC rate for this example is 1.72 BAR per minute.

The Formula for calculating your SAC rate is.

((Starting BAR – Ending BAR) / Depth in ATA) / Duration of test) = SAC Rate

*Remember that your SAC rate is dependent on the cylinder you used. Your SAC rate will be different if you use a different cylinder.

Do you know your SAC Rate? How do you plan to calculate and use this number? Let us know in the comments below.

How Do You Read The Markings On A SCUBA Tank?

By Jose Cernuda

Understanding the Markings on Your SCUBA Tank

Have you ever wondered what all those markings on your SCUBA tank mean? Many people don't know it, but many of the markings that go on SCUBA cylinders are required by law. In the United States, the Department of Transportation regulates SCUBA cylinders. In Canada, it's Transport Canada that regulates SCUBA cylinders. Every country has their own regulatory authority so these two are just examples. 

On most SCUBA tanks the engravings on the shoulder will  indicate the following:

  • Manufacturer
  • The serial number of the cylinder
  • The material the cylinder is made out of (steel or aluminum)
  • Tank capacity (how many cubic feet or liters does the tank hold)
  • Service Pressure (what amount of pressure the tank can be filled to)
  • Original Hydrostatic date (this tells you the age of the cylinder)
  • Department of Transportation or other regulatory markings certifying that the cylinder has passed certain minimum requirements set by the government

Below is an example of markings you’d find engraved on a Luxfer aluminum 80 and next to it an explanation of what the markings mean.

Illustration of the engravings on a luxfer aluminum 80

There are many different possible engravings a cylinder can have depending on the manufacturer's it’s specifications and what part of the world the tank was produced. Because of this, the following chart contains common engravings found on different SCUBA cylinders and what the engravings mean.

Engraving Meaning
184Cylinders service pressure expressed in BAR
207Cylinders service pressure expressed in BAR
230Cylinders service pressure expressed in BAR
237Cylinders service pressure expressed in BAR
2400Cylinders service pressure expressed in PSI
3000Cylinders service pressure expressed in PSI
3300Cylinders service pressure expressed in PSI
3442Cylinders service pressure expressed in PSI
"+"indicates cylinder can be overfilled by 10% when placed next to hydro date
01A20An example of a hydrostatic exam date (numbers will reflect the date)
3AMolybdenum Steel
3AAMolybdenum Steel
3AL U.S. specification for 3-gauge aluminum
3ALMCanadian specification for 3-gauge aluminum
AIndependent Inspector Mark
Catalina Cylinder Manufacturer
DOTDepartment of Transportation (Cylinder passed U.S. specifications)
FaberCylinder Manufacturer
HPIndicated High pressure (3300 to 3500 PSI)
LPIndicates low pressure (2250 to 2400 PSI)
LP95Model Number (also Indicates "low pressure" 95 cubic feet)
Luxfer Cylinder Manufacturer
M9542DOT Manufacturer facility number
P869232An example of a serial number
S040 Model Number (also Indicates 40 cubic feet)
S080Model Number (also indicates 80 cubic feet)
SU7694Canadian special permit number
TC Transport Canada (Cylinder passed Canadian specifications)
TP5250Test procedure for hydrostatic retest (PSI)
XS-80 Cylinder manufacturer and model number (80 cubic feet)

The above list doesn’t show every possible marking. Also, things like model numbers, dates, serial numbers, etc. will vary from tank to tank. In the list above those markings are shown as examples since the actual marking will change with every tank.  

Also, it's important to know that even though the model number will often indicate the cylinder capacity, you should still look up the manufacturer specs when it comes to this. As an example, a Luxfer S080 is typically marketed and referred to as an 80 cubic foot. This number, however, is rounded up. The cylinder actually contains 77.4 cubic feet. You can see the specifications for the most common tanks here

Hydrostatic Testing Stamps

Another common engraving found on SCUBA cylinders is the hydrostatic test date. Many people simply refer to this as the hydro date. The original hydrostatic exam is usually found on the shoulder of the tank together with the other manufacturer engravings and tells you when the cylinder was originally manufactured. SCUBA tanks need to be hydrostatically tested every 5 years. Subsequent stamps are usually somewhere in the shoulder area, but you may need to look around. I've seen stamps in pretty much every location you can think of on a SCUBA cylinder.

Visual Inspection Stickers

Close up of a visual inspection sticker on a SCUBA tank

Visual inspection stickers are another marking you'll commonly find on SCUBA tanks. While obviously not an engraving visual inspection stickers provide useful information about the cylinder. They tell you when the last inspection was performed and whether or not the cylinder has been cleaned for use with Nitrox. 

Nitrox SCUBA Tanks

It's very common to see tanks designated for use with Nitrox. This is usually done with a sticker rather than an engraving. Nitrox tanks are labeled for two reasons. First, so that everyone knows that the tank contains a gas other than air. This way no one will accidentally dive with a tank that they do not know the contents of. Nitrox requires the use of different decompression tables than air and the added oxygen also presents different risks that divers need to be aware of. Second, because Nitrox tanks are often filled with pure oxygen and then topped off with air as part of a partial pressure fill, the tanks need to be cleaned for oxygen. Technically, it's the visual inspection sticker that tells the technician filling the tank that it's clean, but the big Nitrox sticker is also helpful.

Any SCUBA cylinder can be adapted for diving with Nitrox. Most new SCUBA tanks come ready to be filled with Nitrox from the factory. However, if you are purchasing a used cylinder, you may need to have your local dive shop clean the tank and for use with Nitrox along with changing the O-rings to Viton O-rings so that they are compatible with Nitrox. Once this process is completed, the dive shop will indicate that it is safe for Nitrox on the visual inspection sticker. Additionally, many shops will place a Nitrox sticker on the tank to indicate that the cylinder may contain a gas other than air.

Recommended SCUBA Cylinders

Choosing a cylinder that’s right for you involves looking at many factors. Among those factors are:

  • Your breathing rate,
  • Body size
  • Planned diving depth
  • The mix you’re using
  • Your body's buoyancy characteristics
  • How you trim out in the water with your current configuration
  • How much gas you’d like to have in reserve at the end of the dive

These are all factors that go into deciding what SCUBA tank will be best for you. We have an article that goes in-depth into this topic here.

For more information on specific cylinders, we recommend you check with the cylinder manufacturers directly. The “additional resources” tab below contains links to the cylinder manufacturers listed above. You can find information that goes beyond the SCUBA tank size chart there. 

Additional Resources on SCUBA Cylinders

SCUBA Cylinder Specifications

By Jose Cernuda

The chart below contains SCUBA cylinder specifications in both the imperial and metric systems of measurement. This chart is a compilation from many sources. It is intended to be a starting point for comparing different SCUBA tanks, their capacities, dimensions, weight, and buoyancy characteristics. You can go directly to the sources used in compiling this list by clicking on the “additional resources” tab at the bottom of this page.

SCUBA Tank Size Chart

  • Imperial

  • Metric

ManufacturerModelMaterialCapacityFill PressureLength (inches)Diameter (inches)Weight (Lbs)Buoyancy Full (lbs)Buoyancy Empty (lbs)
CatalinaS4Aluminum430007.83.211.9-1.6-1.4
CatalinaS6Aluminum6300010.83.212.6-1.2-1.2
CatalinaS13Aluminum13300012.84.385.7-1.8-0.9
CatalinaS19Aluminum19300017.74.387.8-1.5-0.2
CatalinaS20Aluminum20300013.85.259.2-1.40
CatalinaS30Aluminum30300019.95.2513.6-2.4-0.2
CatalinaS40Aluminum40300025.45.2516.2-1.51.4
CatalinaS45Aluminum45300017.76.8920.3-2.80.5
CatalinaS50Aluminum50300019.46.8921.8-2.41.2
CatalinaS53Aluminum53300019.27.2525.1-3.80.1
CatalinaC60Aluminum60330019.97.2527.3-5.6-1.2
CatalinaS63Aluminum63300021.77.2526.9-2.81.8
CatalinaS80Aluminum77.4300025.97.2531.3-1.64.1
CatalinaC80Aluminum77.4330025.57.2534.7-5.80
CatalinaC100Aluminum100330026.5842-5.22.2
FaberFX15DVSteel15344014.173.946.6-2.42-1.21
FaberFX23DVSteel23344219.53.948.6-2.64-0.66
FaberL27DVSteel27264014.435.4611.7-2.95-1.07
FaberFX40BKDVSteel40344217.77.2414.8-4.51-1.48
FaberL50SDVBSteel50264025.25.5118.9-2.431.24
FaberM71SDVBSteel71330020.476.8428.7-4.350.9
FaberFX80SDVBSteel80344220.877.2428.6-8.05-1.74
FaberHP80Steel 81.7344220.87.2528.3-8.05-1.74
FaberL85SDVBSteel85264025.987.0131.2-3.82.32
FaberL95SDVBSteel95264023.828.0237.2-5.371.69
FaberM100SDVBSteel100349824.217.2438.7-14.11-6.69
FaberFX100SDVBSteel100344225.397.2434.3-8.41-0.59
FaberHP100Steel 101.3344225.37.2524-8.41-0.59
FaberL108SDVBSteel108264026.778.0241-5.022.98
FaberFX117SDVBSteel117344224.218.0238.9-9.12-0.16
FaberHP117Steel 117.8344234.2837.6-9.120.35
FaberL120SDVBSteel120264029.338.0244.9-4.874.07
FaberFX120SDVBSteel120344229.337.2439.2-8.820.65
FaberHP120Steel 120.1344229.17.2539.2-8820.65
FaberHP133Steel 133344226.85842.4-9.081.45
FaberFX133SDVBSteel133344226.788.0242.7-9.081.45
FaberFX149SDVBSteel149344229.538.0246.9-9.412.35
LuxferS006Aluminum6.1300011.13.22.6-1.4-0.9
LuxferS13SAluminum13.2300013.14.46-1.8-0.8
LuxferS019Aluminum19.9300018.64.48-1.30.2
LuxferS030Aluminum30300019.35.312-1.30.9
LuxferS040Aluminum40300024.86.914.9-0.72.4
LuxferS050Aluminum48.43000197.321.3-2.51.1
LuxferS063Aluminum63300021.97.326.9-2.42.4
LuxferS072Aluminum69.63000266.928.5-1.43.8
LuxferS080Aluminum77.4300026.17.331.5-1.74.2
LuxferS80NAluminum77.4330025.87.335.4-30.1
LuxferS100Aluminum98.8330026.2841.1-4.62.8
LuxferS106WAluminum Hoop Wrap106435026.17.433.8-4.83.1
MetalImpactAL06Aluminum5.8300010.93.22.7-1.6-1.12
MetalImpactAL13Aluminum12.8300012.74.46-1.1-0.14
MetalImpactAL19Aluminum18.3300017.254.47.9-1.7-0.38
MetalImpactAL30Aluminum29.1300019.55.2512.3-1.60.68
MetalImpactAL40Aluminum38.8300024.95.2515.3-11.88
MetalImpactAL50Aluminum49.5300019.46.921.5-2.31.54
MetalImpactAL63Aluminum61300021.97.2527.2-2.32.38
MetalImpactAL72Aluminum703000266.927.8-0.94.38
MetalImpactALN80Aluminum76.2300025.47.2533.4-4.11.78
MetalImpactAL80Aluminum77.5300026.17.2531.9-1.54.26
MetalImpactAL100Aluminum98.2300026.25842-5.32.26
OMS / FaberC8Steel7.87264011.253.585-2.23-1.61
OMS / FaberC13Steel132640143.95.9-3.31-2.25
OMS / FaberC20Steel20264019.53.97.5-3-1.5
OMS / FaberC45Steel462640235.517.6-40
OMS / FaberC50Steel50264025.25.519.92-4.8-1.5
OMS / FaberC66Steel66264021725-5.151.67
OMS / FaberC85Steel85264026731-6.70
OMS / FaberC98Steel98264024838-7.730
OMS / FaberC108Steel112264026841-8-1
OMS / FaberC121Steel125264029845-9.50
OMS / FaberC135Steel131264030.7847-10.30.75
Pressed SteelLP-45Steel452640235.519.6-3.7-0.5
Pressed SteelE7-65Steel65344216.757.223.2-6.4-1.5
Pressed SteelMP-72Steel71.2330020.756.930-11.4-6
Pressed SteelE7-80Steel80344219.757.226-9.3-3.3
Pressed SteelLP-80Steel80.62640247.234.4-7-1
Pressed SteelE7-100Steel1003442247.232-8.8-1.3
Pressed SteelE8-119Steel119344224839.3-12.2-3.3
Pressed SteelE7-120Steel1203442287.236.6-10.3-1.3
Pressed SteelE8-130Steel130344225.56842.2-14.6-4.8
Pressed SteelE8-149Steel149344229.37847.5-12.8-1.7
WorthingtonLP27Steel27264014.55.511.9-3-1
WorthingtonX7-65Steel66.4344216.77.2525.1-8.7-3.9
WorthingtonLP77Steel77264023.27.2532.5-6.8-1
WorthingtonX7-80Steel81344219.87.2529.9-9-3
WorthingtonLP85Steel82.9264024.77.2536.8-7.1-0.7
WorthingtonLP95Steel93.3264023.7836.8-7.1-0.7
WorthingtonX7-100Steel99.5344222.77.2533.1-10-2.5
WorthingtonLP108Steel108.6264026.5845.95-10.7-2.6
WorthingtonLP121Steel120264029.2849.9-11.1-2
WorthingtonX7-120Steel120.6344227.77.2539.7-11-2
WorthingtonX8-119Steel123344223.9842.5-10.9-2
WorthingtonX8-130Steel131.4344225.3844.7-11.7-2

The buoyancy of the cylinders above are in salt water. Also, the weight and dimensions do not include the tank valves. 

If you are trying to determine which cylinder you are looking at, it may be helpful to look at our article on understanding tank markings. In it we go in depth into many of the engravings found on SCUBA cylinders. 

Also, if you are in the market for a new tank and want more help with choosing the tank that's right for you you may want to read our article on how to pick the perfect SCUBA tank for you

Also, For more information on specific cylinders we recommend you check with the cylinder manufacturers directly. The “additional resources” tab below contains links to the cylinder manufacturers listed above. You can find information that goes beyond the SCUBA tank size chart there. 

Additional Resources on SCUBA Cylinders

Choosing the best SCUBA Tank for you

How To Pick The Perfect SCUBA Tank That’s Right For You!

By Jose Cernuda

Choosing the best SCUBA Tank for you

Have you ever considered diving with a different size SCUBA tank than the one you normally dive with? Maybe you want to stay down longer so you figure a bigger tank will buy you some more bottom time? Perhaps the tank you always use just seems too big and bulky and you want a smaller, lighter tank that will be easier to handle? A bigger tank equals more gas. More gas may potentially get you more bottom time. How much more? Check out our nifty little calculator below (one of many throughout this article) to find out how much more or less gas you will have. 

  • Imperial

  • Metric

If you look at how much more gas you get by switching from an aluminum 80 (11 liter) to a steel 120 (15 liter) tank and what you want is more gas on your dives then you'd think the decision is a no-brainer. After all, you get 55% more breathing gas from making that switch. You can get even more out of even bigger tanks! However, there are other things to consider. Every SCUBA cylinder has its positives and negatives. You can see a full breakdown of the characteristics of different tanks in our chart of common diving tanks later in this article. 

There’s much more to choosing a SCUBA tank than simply getting a bigger or smaller tank for your needs. By reading this article you'll know more about SCUBA tanks than most divers do and how to choose the best one for you. 

What to consider when purchasing a SCUBA tank?

Many factors go into choosing the perfect  SCUBA diving tank for you. If you choose poorly you could end up with a tank you hate or one that simply sits around and gathers dust because you'll realize after a few dives that you'd rather not use it. . Some of the things you'll need to consider when choosing the tank that's right for you will include the size/capacity of the tank, the material (aluminum vs. steel), the physical weight of the tank, the buoyancy characteristics of the tank in the water, how the tank affects your trim, and, of course, the cost of the tank.

Tank Terminology - Getting To Know The Parts That Make Up Your Tank

Before you learn how to choose the right tank, you must understand the terminology used for tanks and what it all means so that you can fully understand the choices that you are going to make when choosing a cylinder.

Tanks, Botttles, Or Cylinders, What's The Difference?

Depending on where you took your SCUBA classes and maybe where your instructor is from, you may have heard either the term SCUBA tank, SCUBA cylinder or maybe even SCUBA bottle. They are all the same thing. In this article, we use the terms interchangeably. Just to be clear, if you hear someone mentioning any of the terms above, they are talking about the same thing.

Steel vs. Aluminum

All SCUBA diving tanks are made out of either aluminum or steel. Each material has pros and cons which we will explain later in this article. Generally speaking, steel cylinders tend to be more expensive, they also tend to hold more gas than a similarly sized aluminum tank. Steel tanks also generally tend to have better buoyancy characteristics in the water, but more on that later.

Pressure ratings

All SCUBA cylinders have a maximum pressure that they can be filled to. In the United States, we use pounds per square inch (PSI) to measure the maximum pressure. In many parts of the world, BAR is the unit of measurement used. One BAR is roughly equal to 14.5 PSI. 

Tanks come in three varieties when it comes to pressure.

Low pressure (2400 to 2540 PSI – 165 to 182 bar)

Standard (3000 PSI – 207 bar)

High Pressure (3300 to 3500 PSI -227 to 241 bar)

Again, each pressure has pros and cons which you will learn about in this article.

Capacity and Internal Volume

In the United States, all SCUBA tanks have a rated capacity. The capacity of a tank is the amount of gas a cylinder will hold when is full. In the Imperial system we use cubic feet to measure the capacity of a tank. The capacity of a tank is how many cubic feet of gas is inside the tank when filled to its rated pressure. So, as an example, an aluminum 100 cubic foot tank that is rated to 3300 PSI will hold 100 cubic feet of gas when the pressure inside is at 3300 PSI.

In other parts of the world capacity for tanks is expressed as its internal volume. The internal volume is expressed as the amount of water a tank can hold. This is mainly used in countries that use the metric system. So, a 9 liter tank holds 9 liters of water if it were filled with fluid. To determine the amount of gas a tank can hold you simply multiply the size of the tank in liters by its service pressure. So, as an example, an 9-liter tank that is filled to 207 bar will hold 1863 liters of gas when full (9 x 207 =1863). 

To get a better understanding of how pressure relates to volume when it comes to SCUBA cylinders check out our SCUBA tank volume calculator below. Notice on the calculator how, when the tank is full, you have the full capacity of the tank. As you move the slider to the left, the pressure decreases as does the amount of available breathing gas. 

SCUBA Tank Volume Calculator

  • Imperial

  • Metric

The K-Valve

Close up of a K-valve on a tank

SCUBA tanks can be purchased with or without the tank valve. If you are purchasing a SCUBA tank with a tank valve you'll most likely be purchasing it with a K-Valve. Most all modern SCUBA cylinders use a K-valve. There are other types of valves, but their use is a topic for another article. Just know that if someone refers to the K-valve they are talking about the SCUBA tank valve.

DIN vs. Yoke

When you choose a SCUBA tank often the tank will come with a K-valve. That valve comes in two varieties, a DIN fitting or a yoke fitting. Your choice is often determined by the type of regulator that you are using. Yoke fittings are for the clamp-on type of regulator and DIN fittings are for the screw-on type. You can tell the difference because the DIN valves have a larger opening and threading on the inside in order to screw on a DIN regulator. 

Notice how the DIN valve on the left has a large threaded opening for a DIN regulator to screw into. The Yoke on the right does not as yoke regulators are clamped on.

Burst Disk

The bolt in the center is the burst disk. It can be unscrewed and easily replaced.

The burst disc is a valve that screws into the K-Valve itself. It looks similar to a bolt and is there for safety. If a tank is filled to an unsafe pressure above the tank's maximum rated fill pressure, the burst disk will break and safely expel all the gas contained in the cylinder. The purpose is to have the burst disc break before the tank explodes.

Burst discs can rupture due to age or even temperature changes when the burst disk is faulty. When a burst disc breaks, it is LOUD! All of the gas will escape the tank in a matter of minutes. It can be pretty scary if one goes unexpectedly.

Gas Mixtures

Because SCUBA tanks can hold air, nitrox, trimix, argon or, even pure oxygen when used for decompression in technical diving, it’s common for divers to refer to what’s inside as gas. Saying a cylinder is filled with something like air or oxygen is usually only done so when you know what the content of the gas inside the tank is, and you are referring to it specifically.

Inspections

SCUBA diving tanks must be inspected periodically to ensure that the metal is structurally sound and can be filled safely by a SCUBA compressor. Because SCUBA cylinders contain pressurized gas inside, if the integrity of the metal were compromised, the tank can explode when being filled.

In the United States tanks are visually inspected yearly and hydrostatically inspected once every five years. After the visual inspection is passed, the tank is usually marked with a sticker indicating when the visual inspection was performed. When Hydrostatic inspections are passed the tank, is physically engraved with the date of the hydrostatic test. The hydrostatic test is frequently abbreviated to just hydro. It's common to refer to this exam as the hydro test or the hydro date. .

Tank Engravings

All tanks have markings engraved on the shoulder of the cylinder. These markings indicate things like the manufacturer, material of the tank (aluminum or steel), serial number, working pressure, and the original hydrostatic test. For more information on how to interpret these markings check out this article


Tank Labels

Other than the visual inspection sticker, it’s common practice to label tanks that are designated for use with Nitrox or other gasses such as Trimix. It’s also a common practice in the technical diving community to place labels on tanks indicating the mixture of gas that’s inside and its maximum operating depth.

Tank Coatings

In the presence of moisture, aluminum will oxidize and steel will form rust.

For this reason, steel tanks have a zinc coating. Depending on the manufacturer, the coating may either be a zinc dipped coating that is applied during the galvanization process of the tank, or a hot zinc spray coating that is then protected by epoxy paint. This is done to protect the tank from rust.

Aluminum cylinders are either painted, left natural, shot blasted, or brushed. Many people believe aluminum tanks are best left unpainted because once the paint begins to chip, moisture can get under the paint and oxidize faster than if no paint had ever been applied in the first place. Also, because chipped paint can end up in the ocean, many manufacturers have moved towards using paints that are more environmentally friendly. Many believe these paints do not adhere as well as the paints used on tanks of yesteryear.

Whether or not the paint helps the exterior of aluminum tanks to avoid rusting is a topic for debate. My personal preference for aluminum cylinders is no paint at all since, sooner or later, the paint will chip and scratch no matter what.

Tank Boots

Both Aluminum and Steel SCUBA tanks can have tank boots. A tank boot is a rubber or plastic sleeve that goes around the bottom of the tank. The boot's purpose is to protect the surfaces that the tank is placed on.

Because a tank is a heavy piece of metal, a tank without a boot can damage floors, the fiberglass on a boat, and even the cement inside of a swimming pool. Also, because the bottom of most steel cylinders are curved, tank boots make it so that you can stand up the tank. Notice how the steel cylinder in the image is curved. If it were not for the tank boot, you would not be able to stand this tank up. 

The drawback of tank books is that they can accumulate water and accelerate the oxidation process. For this reason, many divers choose to not have boots on their tanks.

Steel Vs. Aluminum

Now that you understand the tank terminology you can begin to figure out what tank(s) will be best for you. One of the first things you need to consider is whether to get a Steel SCUBA tank or an Aluminum SCUBA tank. Each has its pros and cons.

Aluminum Tanks

Most people begin diving with an aluminum tank. The most common tank is the aluminum 80 (11 liter) cylinder. Many dive boat operators and dive shops use this tank because 80 cubic feet of gas is enough to do most recreational dives safely, this cylinder is widely available and it’s also one of the cheapest tanks you can buy.

As a side note, the aluminum 80 does not actually contain 80 cubic feet of gas. Technically it contains 77.4 cubic feet of gas when filled to 3000 PSI. The number is rounded up to 80 by almost everyone. Two of the most popular manufacturers of these tanks are Luxfer and Catalina.

Just because you began diving with an aluminum cylinder does not mean that it is the best option for you. The main positive of using aluminum tanks is that they are cheaper and lighter than steel tanks.

For some specialized types of diving such as sidemount and technical diving, this is often the preferred option, but that is beyond the scope of this article.

Because aluminum is less dense than steel, many aluminum tanks will float when they are empty. You have to remember that the gas in the tank also has weight to it. As you consume the gas the tank will become lighter throughout the dive. All tanks will become lighter throughout the dive as you consume the gas contained inside. In the case of aluminum tanks, the shift in buoyancy from the start of the dive to the end of the dive is enough that most divers need to add weight to their BCD or weight belt to offset the positive buoyancy.

The slider below illustrates how an aluminum 80 goes from being negatively buoyant when full to being positively buoyant when empty. The concept is the same in the metric system even though the units of measurement are different. 

Keep in mind that many divers need ballast to be able to descend in salt water. If a diver were to rely on the negative buoyancy provided by the gas inside a tank at the start of a dive, at some point during the dive, as the gas is consumed, the diver may become too positively buoyant to be able to stay underwater. This can be a dangerous situation. You can see in the video below how the same aluminum cylinder will have completely different buoyancy characteristics depending on the amount of gas that's inside. 

Something else to consider about aluminum tanks is that they hold less gas than a similarly sized steel cylinder.

Finally, because aluminum is a weaker material than steel, many dive shops will not fill older aluminum tanks.

The good thing about aluminum tanks is that they are cheaper and lighter on the surface than steel tanks. 

Pros: Familiarity, Cheap, lighter to carry around on the surface

Cons: Unfavorable buoyancy characteristics, you need to add ballast to offset its buoyancy, they hold less gas than steel cylinders and tend to have a shorter lifespan.

Steel SCUBA Tanks

Many experienced SCUBA divers as well as technical divers prefer steel cylinders. The main reason is that they hold more gas than a comparably sized aluminum tank and they also usually have more favorable buoyancy characteristics.

Because steel is a denser material than aluminum, steel SCUBA tanks tend to remain negative even when they are empty. This means you can use less ballast on your SCUBA rig. Also, because the weight that you take off of your rig is being distributed across your back, you will usually trim out better in the water than you would with a comparable aluminum cylinder (more on this later).

Also, steel tanks are available in larger capacities than aluminum tanks. If you need more than 100 cubic feet of gas in a single cylinder, then steel is the only choice.

As mentioned previously, steel SCUBA tanks also tend to have a longer lifespan than aluminum tanks. For this reason, many divers believe that, when you look at the true cost of owning steel, it isn’t more expensive when you consider the longer life.

The downside to steel SCUBA tanks is that they are more expensive to purchase. Also, you need to be careful to make sure you rinse off your tanks if diving in saltwater and pay attention to any water that may collect in the tank boot if you have one. This can lead to corrosion over time. You also should, as with all cylinders, never drain them completely to avoid the possibility of moisture entering the tank. Finally, steel cylinders tend to be heavier out of the water than aluminum cylinders. 

Pros: Hold more gas than a comparable aluminum tank, better buoyancy characteristics, better trim properties, only choice for larger capacities

Cons: More expensive, can corrode if not maintained, heavier to carry around on the surface

Chart of common SCUBA cylinders

Below is a chart of some of the common SCUBA cylinders used by divers. This list is not comprehensive. However, if you compare the cylinders you should begin to get an idea of how different tanks have different buoyancy characteristics. For a more comprehensive list, check out our article dedicated to tank specifications

  • Imperial

  • Metric

ManufacturerModelMetalVolumeFill PressureLength (inch)Diameter (inch)Weight (lbs)Buoyancy Full (lbs)Buoyancy Empty (lbs)
CatalinaC60Alumium60330019.97.2527.3-5.6-1.2
CatalinaS63Alumium63300021.77.2526.9-2.81.8
CatalinaS80Alumium77.4300025.97.2531.3-1.64.1
CatalinaC80Alumium77.4330025.57.2534.7-5.80
CatalinaC100Alumium100330026.5842-5.22.2
FaberM71SDVBSteel71330020.476.8428.7-4.350.9
FaberFX80SDVBSteel80344220.877.2428.6-8.05-1.74
FaberL85SDVBSteel85264025.987.0131.2-3.82.32
FaberL95SDVBSteel95264023.828.0237.2-5.371.69
FaberM100SDVBSteel100349824.217.2438.7-14.11-6.69
FaberFX100SDVBSteel100344225.397.2434.3-8.41-0.59
FaberL108SDVBSteel108264026.778.0241-5.022.98
FaberFX117SDVBSteel117344224.218.0238.9-9.12-0.16
FaberL120SDVBSteel120264029.338.0244.9-4.874.07
FaberFX120SDVBSteel120344229.337.2439.2-8.820.65
FaberFX133SDVBSteel133344226.788.0242.7-9.081.45
FaberFX149SDVBSteel149344229.538.0246.9-9.412.35
LuxferS063Alumium63300021.97.326.9-2.42.4
LuxferS080Alumium77.4300026.17.331.5-1.74.2
LuxferS80NAlumium77.4330025.87.335.4-30.1
LuxferS100Alumium98.8330026.2841.1-4.62.8

High-Pressure Vs. Low-Pressure

As you look at the chart above you should notice that different tanks have different service pressures. The service pressure is the maximum pressure a tank can be filled to. The capacity of the tank is measured at its service pressure in the imperial system. In the metric system you multiply the capacity of the cylinder by its fill pressure in bar. 

Below are the definitions for low, standard, and high-pressure:

Low-pressure (2400 to 2540 PSI – 165 to 182 bar)

Standard (3000 PSI – 207 bar)

High-Pressure (3300 to 3500 PSI -227 to 241 bar)

This brings up the question, is there any advantage to low pressure vs. high-pressure tanks?

In general, high-pressure tanks put more stress on O-rings and the internals of your SCUBA regulator. With modern regulators and if you are regularly servicing your equipment as recommended, this should not be a problem.

The only disadvantage high-pressure tanks may happen if you are filling your tanks with Nitrox from a provider that uses a partial pressure filling system and does not have a gas booster. If they are using this system and they are running low on oxygen, they may not be able to get the oxygen level high enough in your tank for you to reach your desired mix.

This can also happen with standard pressure and low-pressure tanks it’s just that because you need to reach a higher pressure with the high-pressure tanks, they are the most affected.

Another disadvantage of high-pressure tanks is that, if the dive shop you go to does not regularly fill high-pressure tanks, they may mistakenly under-fill your tank. This is easily remedied by checking your tanks before you leave the shop.

The big advantage of course is that you get more gas with high-pressure tanks.

Some people prefer low-pressure tanks because they are not as negatively buoyant as high-pressure tanks.  Here, your gear configuration and your buoyancy requirements will come into play. Another reason for choosing low pressure tanks for some, is because they place less stress on your regulator. 

One thing to be aware of if purchasing a low-pressure tank is the plus rating. When many low-pressure tanks are first sold, they are technically rated to 2400 PSI. The original hydrostatic test then has a plus rating that allows them to be over-filled by 10 percent. This plus rating is indicated by a “+” after the original hydrostatic date. This additional 10 percent brings the working pressure to 2640 PSI. When they are sold, they are marketed at the capacity reached at 2640 PSI (with the plus rating).

The image to the right shows the original hydrostatic exam performed on a steel cylinder. This hydro exam was performed on January of 2003. This is indicated by the 01 and the 03 respectively. The "+" sign after the date lets the person filling the tank know that this cylinder can be overfilled by 10 percent. 

Sometimes when you have the hydrostatic testing done on the tank years later the operator will not conduct the test for the plus rating. If the subsequent hydrostatic test does not have this plus rating, then the tank may not get filled to its original capacity by some dive shops.

DIN Vs. Yoke

When purchasing a SCUBA cylinder, you’ll often have a choice as to the type of fitting you want for your K valve. The choice will most likely be determined by the type of regulator that you own. 

As mentioned previously, the K-valve that comes on a SCUBA cylinder can be either a DIN or Yoke fitting. You can see in the image below the difference in how yoke regulators are clamped on and DIN regulators are screwed on. 

The Yoke Valve

The Yoke Valve is a clamp-on type of valve. It is the earliest type of valve used by the original Aqua Lung SCUBA regulators. The yoke style regulator is also sometimes called an A-Clamp. The only real advantage to this type of valve is that clamping on your regulator is slightly faster and easier than screwing it on. It’s not a big deal however, we’re only talking about a few seconds difference when setting up your rig.

SCUBA DIN Valve

The DIN valve is a screw-on type of valve. They are a newer type of fitting and are gaining popularity over time. The DIN fitting is more secure which means it is less likely to leak. Also, because there isn’t a clamp sticking out of the back it’s less likely to get knocked loose during the dive. DIN valves are preferred for this reason by technical divers.

DIN Valves come in 2 varieties: 200 BAR and 300 BAR. The difference is that the threading on the 300 bar valves are a bit deeper to accommodate more threading and hence higher pressures. You can fit a DIN regulator made for 300 BAR into a 200 bar valve without issue. You can see in the image below how the same regulator fits more snugly on the 300 bar valve but has some threading exposed when placed on a 200 bar valve. 


If you have the choice as to what kind of valve to get with your SCUBA TANK our recommendation is to get a 200 bar DIN valve with a donut insert. This is sometimes referred to as a convertible DIN valve. You can see an image of one below. 

The donut insert adapter converts a 200 bar DIN valve into a yoke valve. This way you can have the flexibility of using either regulator. This is always convenient if you need to lend your tanks to a dive buddy who doesn’t have the same type of regulator set up that you do.

Choosing a Tank Capacity

Now that you know about all the parts of a tank, the materials it is made of, and the types of valves you can get with one, it’s time to begin to figure out what the best tank size is for you.

The capacity of the cylinder you choose is determined by your breathing rate, the depth you plan to dive to, and how long you plan to dive to a particular depth. You also need to factor in the amount of gas you’d like to have in reserve in addition to the gas you’ll consume throughout the dive.

Your Surface Air Consumption (SAC) Rate or Respiratory Minute Volume (RMV)

The most precise way for you to figure out how much gas you will consume is by knowing your Surface Air Consumption (SAC) rate or Respiratory Minute Volume (RMV). Both measurements are used to measure the rate at which you consume the gas inside your tank.  We wrote an in depth article explaining the difference between the two here. The main difference between the two measurements is that SAC measures your breathing rate in PSI per minute (BAR per minute), and RMV measures your breathing rate in cubic feet per minute (liters per minute). Your SAC rate is tied to the tank you measured your breathing rate on. For this reason, we prefer to measure breathing rate in RMV. Most people in the dive industry use both terms interchangeably. 

Your RMV rate is the amount of gas you consume per minute while diving. The number is expressed at the surface. So, as an example, a diver with an RMV rate of 1 Cubic foot per minute can expect to consume 2 cubic feet per minute at 33 feet, 3 cubic feet at 66 feet, and so on…

If you know this number, you can use it to estimate how much gas you will need for any given dive. 

Planned Depth

To determine the correct tank size, you need to know what depth you plan to dive to. The deeper you go the faster you will consume your gas due to the increase in atmospheric pressure. This is why it is common for experienced divers to use bigger tanks for deeper dives.

Time at Depth

More time underwater equals more gas consumed. This is especially true on deep dives.

If you are at 99 feet (10 meters) for example, you can expect to be breathing 4 times the amount of gas that you would be at the surface with each breath because of the increased atmospheric pressure.

One way to plan for time at depth in recreational diving is by looking up the no-decompression limits at the depth you plan to dive to on a decompression table. You can then use the maximum time allowed at the given depth. This does NOT mean you should dive to the absolute limit, it’s just a way of estimating the amount of gas you might need conservatively.

Because most dives end up being multi-level dives another way to estimate the gas you’ll need on your dives would be to use your dive data from a dive computer and estimate how long you tend to dive at a particular depth.

Either way, it’s best to over-estimate the amount of gas that you will need since having more gas than what you need will only make your diving safer.

Gas Needed For A Dive Calculator

  • Imperial

  • Metric

Reserve Gas

Once you know the gas you will need at depth, you should add in additional gas as a reserve. We all learned in our entry-level SCUBA course that you never dive until a tank is empty. It’s common for dive operators to tell divers they should be back on the boat with no less than 500 PSI or 35 Bar. This is usually assuming an 80 cubic foot (11 liter) tank. As stated earlier, it’s best to over-estimate the gas you’ll need. It’s also a good idea to try to have more reserves than the minimum.

Estimating Gas Without Your SAC or RMV Rate

If you do not know your SAC or RMV rate, a less precise way to estimate your gas requirements would be to look back at your dive log and estimate the amount of gas you would need to complete the type of dive you want to do.

Let's say as an example that you have done a dozen or so dives to a shipwreck at 100 feet (30.5 meters) using Nitrox and an aluminum 80. Your average dive was around 24 minutes returning to the boat with 500 PSI (35 BAR). You would like to have more bottom time, so you know you will need a bigger tank.

Following our example, the NDL at 100 feet (30.5 meters) for 32% Nitrox is 30 minutes (this number varies depending on which table you look at). This means you’d like to get 6 additional minutes or 25 percent more time. So, you’ll need a tank that has at least 100 cubic feet of gas to accomplish this.

Round-Up the Estimated Amount of Gas

It’s important to realize that you’re better off having more gas than what you need for a dive than not having enough. For this reason, when in doubt about choosing two similar tanks you’ll usually be better off choosing the larger size.

Tank Buoyancy, Trim & Size Characteristics

Tank Buoyancy

Once you know how much gas you need to be able to do your desired dives, you need to consider the buoyancy characteristics of the tanks that hold the amount of gas that you need. Different tanks have different buoyancy characteristics.

In the video below you can see how I was able to add just enough weight to an aluminum 80 to get it to be neutrally buoyant in fresh water. This is an exercise I suggest you do for yourself with the tank that you dive. You want to know exactly how much weight (if any) you might need to offset the buoyancy of your tank at the end of the dive. Do not rely on manufacturer specifications or SCUBA charts! We've found that those numbers can be off in the real world when testing for ourselves. 

Note that the buoyancy characteristics of tanks on most graphs are usually for saltwater diving. Fresh Water will affect your buoyancy and the buoyancy of the tank you use. You'll need less lead in fresh water than you would in saltwater. Tables, like the one on this page should only be used to compare similar tanks and get an idea of the cylinder you want to use or purchase. You should perform your own buoyancy check for your tank as shown in the video above. 

If you’ve done a proper buoyancy check and know how much lead you need to be properly weighted then you might want to consider using a steel tank to offset some of the ballast that you’re using either in your weight belt, integrated weights, or even in the form of a stainless steel backplate. Doing so has three advantages. First, by spreading the weight across your back you'll trim out better (in a more horizontal position) in the water. Second, by shedding some of the ballast you need to dive, it'll be easier to carry your dive gear. Finally, if you move to a steel tank you'll usually be able to get a tank with a higher capacity (more gas) in a similar size as an aluminum tank. 

Something else to consider is if you know you need little to no weight, or if you are diving in freshwater, then you may need to consider the amount of lift your BCD or Wing provides and whether it’s enough to offset the negative buoyancy of the tank that you are considering.

Similarly, if you are using a thick wetsuit or a drysuit when you go diving then you need to consider the buoyancy characteristics of the suit and undergarments you are using. Here it may be advantageous to choose a cylinder that's more on the negative side to help offset the positive buoyancy created by your suit. 

Proper weighting is a completely different topic. For more information, you may want to see this in article.

Tank trim Considerations

Something else to consider when choosing your tank is how it will affect the way your body trims out in the water.

Consider the diagram below. The diver on the left is using aluminum 80 (11 liter) tank while the tank is still full and negative. Notice where their center of gravity is. The diver on the right is using a high pressure steel 80 (10 liter) tank. Both tanks hold the same amount of gas when full. Notice however, that because the high pressure steel tank on the right is shorter, the center of gravity shifts. It helps the diver maintain a more horizontal and streamlined position during the dive. This does not mean that choosing the right tank is the only way to properly trim out a diver but it is a factor to consider. 

Tank Size Considerations

How large or small a Cylinder is will affect how easy it is to carry and store your tank. A high-pressure steel 133 cubic foot tank for example, is both larger heavier, and bulkier than a Aluminum 80. The 133 cubic foot tank will however give you 55 additional cubic feet of gas during your dive. You can see the size difference in the image to the left. 

If you are considering getting two different tanks that each have a different diameter you should know that you will have to adjust the tank strap on your BCD when you switch from one tank to the other. It’s not a big deal, but it is a small inconvenience you should be aware of. You can see that difference in diameter in the picture above. 

Hidden Tank Costs

Overall if you dive enough it’s usually more economical to own your tanks. It’s also best because you can have the tank size and weight that best suites you.

You should, however, be aware of the costs associated with owning a tank. Over the life of the cylinder, you’ll have to pay for more than just the gas fills.

Visual & Hydrostatic Inspections

Every country has regulations regarding how compressed cylinders need to be maintained. In the United States, the Department of Transportation (DOT) regulates SCUBA cylinders. In the US, SCUBA cylinders need to be visually inspected yearly, and hydrostatically inspected every 5 years. This is a cost you should factor into owning a tank. Prices for this varies, so check with your local dive shop.

The visual inspection is performed by dropping a special light into the tank to check for any signs of corrosion, cracking, pitting or anything else that may affect the structural integrity of the cylinder.

Some service technicians may also perform a visual eddy as part of the visual inspection. This is an additional test where an electrical current is run through the neck of the tank in order to further check the structural integrity of the tank.

When a visual exam is passed a sticker is placed on the tank to indicate the date when the visual inspection was performed and passed. You can see an example of a visual inspection sticker from a local dive shop in the photo to the right. 

A hydrostatic exam requires a special machine. There are several ways to perform this test. The most common is a machine where the tank is placed into a steel container that is surrounded by water. The machine then pressurizes the SCUBA cylinder to five thirds of its working pressure. The technician will measure the expansion of the metal under pressure. If the tank is within the allowed tolerances for the exam, it will pass the test.

When a hydrostatic test is passed the tank is permanently engraved with the date of the hydrostatic test.

Both the visual and hydrostatic tests are essential to make sure SCUBA cylinders are safe to fill. Dive operations can deny filling any SCUBA cylinder they feel may be unsafe to fill. This is because, if a SCUBA cylinder bursts while being filled, it’s like a bomb exploding. It can kill or injure anyone who is unfortunate enough to be nearby as well as cause significant property damage.

Valve maintenance

Over time the O-rings and other internal parts of a SCUBA valve can become worn and even corrode. Your local dive shop will inspect the valves at a minimum when you do the visual inspection. From time to time, the valves will need to be rebuilt since, just like your regulator, they are mechanical and need to handle 3000 PSI (207 BAR) or more regularly.

Tank & Valve Cleaning for Nitrox

If your SCUBA tank will be filled with Nitrox, you’ll most likely need to have the tank and valve cleaned for Nitrox. Most SCUBA cylinders come cleaned for Nitrox from the factory, but once the first hydrostatic test is done, you’ll need to clean the tank afterward.

Additionally, many dive shops will require you to label your tank with a “Nitrox” sticker. This is so that everyone knows that the tank contains a mixed gas and to avoid anyone confusing your tank for an air tank.

Renting Vs. Buying

When to Rent

Should you even buy a tank at all? If you have to fly to get to all of your diving destinations, then owning a tank doesn’t make sense. Also, if you live far enough from a dive shop that driving there to fill your tanks is a major inconvenience, then you’ll probably also be better off renting your tanks when you dive.

Another thing to consider is how often you dive. If you only dive several times a year all the hassle of filling and maintaining the tank may not be worth it to you.

When to Buy

If you dive fairly regularly and live close enough to a dive shop that can fill your tanks, you’ll probably want to own your tank.

Below are just some of the advantages of owning your tanks:

  • You can match the size of the tank to the gas that you need for a dive
  • You can choose a tank that has better buoyancy characteristics
  • Your tank can help you achieve better trim in the water
  • You can have more control over the mix of gas inside the tank and not be limited to what may be available for rent
  • You can choose the type of tank valve that you prefer

What to Do If You Can't Buy

If buying a tank doesn't make sense because you travel to dive or it's simply inconvenient, it doesn't necessarily mean you need to settle for whatever the dive operator gives you. Many dive operators rent out different size tanks and steel tanks as well as aluminum ones. If you want to dive something other than the standard aluminum 80 (11 liter) you should ask. If the operator you ask doesn't carry a variety of different tanks then you might want to ask a different dive operation that goes to the same sites. It might be as simple as making a phone call or browsing their web site. 

How Many Tanks Do You Need?

How many tanks you’ll need will depend a lot on how often you dive, what types of dives you do, and what you can afford.

If most of your diving is going to be using commercial dive operators, you’ll probably want to start with 2 tanks since most dive trips consist of 2 separate dives.

Your first 2 tanks should be able to hold enough gas for the deepest dives you plan on doing. Since you’ll only have 2 tanks, you’ll want to be able to do both deep and shallow dives. It’s better to have bigger tanks that you can also use on shallow dives than to get tanks that are too small for you to use on deeper dives.

If you do a lot of diving in both shallow water and deep water, you may want to consider owning 4 tanks. One set of tanks for the shallow dives and another for deeper dives. This is a personal choice if you want to go this route. The advantage of having smaller tanks for shallow dives is that they are easier to handle and may trim you out better in the water.

For most recreational divers 4 tanks are more than enough to cover just about anything they might want to do.

Tank Maintenance

A SCUBA diving tank is a long-term investment. Regardless of which cylinder you decide is best for you, you’ll want to take care of it so that it can last as long as possible. Below are some suggestions to help get the most life out of your SCUBA tank.

Rinse after every use

If you are diving in salt water, you’ll want to rinse the tank off after every use. Saltwater left on tanks can accelerate the oxidation process. Don’t forget to rinse off the tank valve thoroughly since it contains moving parts.

Never completely drain your tank

The inside of your SCUBA diving tank is particularly vulnerable to oxidization if moisture gets in. Luckily the easy way to avoid this is to never completely drain your SCUBA tank.

Even if you never completely breathe down your tank during the dive it’s still possible for the tank to drain after the dive. A small regulator leak or even a low-pressure inflator that’s leaking ever so slightly can slowly drain the tank if it’s not disconnected or at least turned off. So, make sure you close your SCUBA tank valve after the dive is complete.

Periodically remove your boots

As mentioned earlier tank boots tend to collect water inside of them. If you choose to have boots on your tank, consider removing them when you are rinsing your tank and allowing the tanks to dry without them. If this is too much of a hassle to do every time at least check periodically to ensure there is no oxidation forming under the boots. Better to catch it early and fix it than to allow the oxidation to grow.

If the valve got wet, open and close it before connecting a regulator to it

This one isn’t strictly for your SCUBA tank, but it’s worth mentioning. If your tank gets wet because of rain, because it was dunked in a rinse bucket, or any other reason, you want to make sure the moisture that may be in the valve doesn’t get into your regulator and damage it. A quick opening and closing of the valve should shoot any moisture that’s trapped inside the valve out so that it doesn’t escape under pressure into your regulator’s first stage.

Don’t forget your visual and hydrostatic inspections

Dive shops won’t fill your tanks if they are not current on their inspections. There’s nothing worse than going in to get your tank filled a few days before a planned dive only to realize you can’t get your fill because it’s due for a hydro. It’s a good idea to set a calendar reminder for when your visual and hydros are due so you don’t get caught by surprise

If you suspect water entered a tank, take it to your dive shop as soon as possible

As mentioned before, moisture inside a SCUBA diving tank can ruin the tank. Your dive shop can inspect the inside of your cylinder to see if any damage was caused by moisture inside the tank. If there is oxidation there is a process called tumbling which can be performed to remove the oxidation and restore the tanks for continued service.

If a Cylinder is involved in a fire, a significant car accident, or anything else that may affect its material strength, have it tested

It’s always better to be safe than sorry. All of the above can weaken the material of a SCUBA tank. If your tank was involved in a house fire or anything that may weaken it, then you should let your local dive shop know and have the tank tested before having it filled. Anything that affects the structural integrity of the tank's metal can be extremely dangerous if the tank explodes while it is being filled. 

Tank Under-fills - Why doesn’t my dive shop fill my tank to its service pressure?

One of the complaints many divers have is that when they check their tank at the dive site it isn’t full. Below are several reasons why this may happen.

Hot Fills

When SCUBA tanks are filled with compressed gas they tend to heat up. Ideally SCUBA tanks should be filled slowly to avoid tanks getting too hot. However, no matter how slowly they’re filled, SCUBA tanks will usually heat up somewhat while being filled. This heat causes the molecules of gas inside the tank to expand somewhat producing a higher pressure. Once the tank cools down, the pressure drops a bit and can cause you to have a fill that is less than the pressure that was read when it was hot.

The best way to avoid this is to drop your tanks off with plenty of time so that your tanks can be filled properly and so that they can cool off. Then make sure you check your tanks before leaving. If they are under the rated service pressure, you can always ask to have your tank topped off.

Cold Temperature Outside

Just as hot air expands cold air will contract. A tank that was filled at service pressure in a warm environment can appear to have less gas when taken outside if it’s cold. This is also common if you are diving in cold water. It’s something to keep in mind when selecting your SCUBA tank. If you frequently dive in cold water you should account for the fact that your tank will most likely be under its full service pressure when you enter the water because of the cold environment. 

The compressor operator is unfamiliar with your SCUBA tank

From time to time you may have a situation where the person filling the SCUBA tanks incorrectly assumed the service pressure of your tank. They may be used to filling all tanks to 3000 PSI and your tank has a service pressure of 3300. Maybe they saw that your tank was a low-pressure tank but missed the “+” rating on it and only filled it to 2400 PSI instead of 2640. Whatever the reason, this is why you should always check the pressure in your tanks before leaving the dive shop.

How to Store and Transport Tanks

Always lay your tank down

Because SCUBA tanks contain compressed gas, it’s always best to lay them on their sides to avoid a tank tipping over and possibly damaging the valve. It is possible that if a tank fell and damaged the valve on the way down that the damaged valve now leaking compressed gas could cause the tank to move violently and cause further damage or even injury.


Always leave some gas inside the tank

As mentioned previously, SCUBA tanks should never be completely drained. This is to avoid the possibility of moisture entering the tank. If SCUBA gear is attached to a SCUBA cylinder, make sure the valve is completely closed.

Always secure your SCUBA tanks when transporting them

You should never allow tanks to roll around in the trunk of a car or the bed of a truck. An unsecured tank’s valve can easily get hit and begin to drain. There’s nothing worse than coming to a stop in your car hearing the tanks in your trunk shift around and then suddenly hearing the hissing of gas leaving your filled SCUBA tank.

Securing your tanks can be accomplished by using a ratchet tie-down, using a portable cylinder rack (usually made out of foam or PVC), or simply wedging the tanks with your dive bag or other gear.


Conclusion

There are a lot of factors that go into choosing the tank that’s right for you. Some of the factors that you need to consider when choosing a tank are the amount of gas you’ll need for the dives you’ll be doing, the buoyancy characteristics of the tank you choose, and how the tank will trim you out in the water. Additionally, you should also consider the type of SCUBA tank valve you’ll need, whether or not to dedicate the tank for Nitrox use, and of course price. Choosing the right SCUBA cylinder can help you have longer more enjoyable dives. It’s one of the pieces of dive gear that most influences your diving. 

What SCUBA tank do you dive with? Are you looking to change to a bigger or smaller tank? If so, why? Let us know in the comments below. 

Additional Resources on SCUBA Tanks

How to Find The Perfect Dive Buddy and Use the Buddy System So That Your Next Dive Will Be Amazing

By Jose Cernuda

Two SCUBA Buddies Gearing Up

Every experienced diver knows buddy diving is about much more than just pairing up with another certified diver on the boat.

A bad dive buddy will ruin what would otherwise have been an amazing dive. They can even put you into a stressful or even dangerous situation.

Choosing a dive buddy is one of the most important things you need to do to have fun and safe dives.

So, if you’ve ever wondered how to find and choose a great dive buddy, or how you can use the buddy system so that you are a great buddy yourself, then you’ll want to read on.

What is a dive buddy?

In SCUBA diving, one of the first things that you learn is that you always dive with a buddy. The purpose of the dive buddy is to increase your safety throughout the dive.

The idea is that by having a competent dive buddy with you that person in essence acts as a safety diver for you, and you in turn act as a safety diver for them.

By having two competent divers pair up you now have a redundant gas supply as well as an additional set of eyes, ears, and even a second brain to process what is happening and make good decisions underwater.

Your dive buddy is the person you dive with that provides redundancy, an added level of safety for you and even makes your dives more fun!  

What is a buddy team?

Buddy Team

Now that we know what a dive buddy is, you might be wondering “What is a buddy team”?

A buddy team is two to three divers that team up to dive together. A buddy team should never be any larger than three divers.

The reason why a buddy team should never be larger than three is that once your team becomes larger than three divers it becomes easier to lose track of each other and to lose a member of the team.

If you are diving in two as a buddy pair, then each diver is responsible for keeping an eye on the other diver throughout the dive. If one of the divers were to have an emergency, it would be easy for the buddy to spot it because they only have one person to look after throughout the dive.

Unfortunately, sometimes there is an uneven number of divers going on a dive and having just buddy pairs is impossible. This is when diving in a team of three comes in.

When diving in a team of three, each diver is responsible for keeping an eye on the other two divers in the team. As you can see, the more people are in a team the harder it becomes to keep an eye on everyone and manage an emergency should one arise. This is why we limit buddy teams to just three divers max.

If four divers are going on a dive together then two teams of two divers each should be established. Everyone can dive together, but the buddy teams need to be established before the dive.

How to Find A Dive Buddy?

There are many places to find a good dive buddy. Looking for a dive buddy depends on your specific needs. Maybe you’re going on a vacation and you want to slip in a few dives but the person you are going on vacation with doesn’t dive. That’s different than if you’re looking to do more diving in the long term and want someone to go on dives with regularly. Here are some places to look for a dive buddy.

Your local dive shop

 If you live close to a dive center this is often a great place to meet other divers. The staff at the dive shop will often know who is looking for a dive buddy for a specific trip or even call people on your behalf to try to set up a dive. Additionally, if both you and the person they pair you up with both did your training at the same shop there’s a good chance that because of the similar training your gear will be similar, your underwater hand signals will be the same and you’ll have the same pre-dive buddy check procedures already in place. This makes everything simpler and smoother.

Your local dive club

Many cities have local dive clubs that meet regularly to dive, give presentations, and even share in meals and drinks. This is another great place to meet and find dive buddies. You can find out about local dive clubs through your local dive shop, local dive operators, social media searches and using google to search for local dive clubs in your city. 

Online Forums & Facebook Groups

Another place to find dive buddies is the internet. Forums such scubaboard.com have dedicated sections for finding dive buddies. You can also try Facebook groups dedicated to SCUBA diving. There are entire web sites such as divebuddy.com which are dedicated to finding a dive buddy. If you are single and looking to date a SCUBA diver there are even sites such as singledivers.com for that.

Continuing education

Taking SCUBA courses is another way to find new dive buddies. The advantage here is that you will be finding someone who is local, is also interested in learning more about diving, and if the class is a specialty course the person will also be interested in the same type of diving that you are interested in.

Dive boat operator

It’s common for divers to show up for a dive without a dive buddy and to have the divemaster or captain pair up the single diver either with another single diver or with an established buddy pair. If you choose to go this route you should check first before simply showing up. Not all dive boat operators will pair you up with a buddy team if there isn’t another single diver, and some may insist you pay to have a divemaster guide you. Simply showing up to the dive boat and blindly being paired up with a dive buddy should be your last option since you have no idea what who you will end up with as your dive buddy.

Hiring a professional

Sometimes the best option is to have a personal guide. This may be especially true if you are vacationing and want someone who can show you all the cool spots to ensure you don’t miss anything. It may also be a good idea if you are traveling and don’t have a lot of experience. By diving with someone who is a professional you may get pointers on your diving technique and gain valuable experience as you build your confidence up. It also ensures you are getting a competent dive buddy should something go wrong. 

Long Term Dive Buddies (what to look for)

It’s one thing to find a buddy to pair up with for a dive trip you’ll be doing on a vacation, it’s another to find a long-term dive buddy to go diving with often and to share your passion for SCUBA diving with over many dives.

If you’re trying to find someone to dive with over the long run here are some things to consider when finding that person.

Do they live close to you and have the time to go diving? 

If a lot of your diving will be local diving, you’ll want your long-term dive buddy to live close enough to you and the dive sites you’ll be diving together so that it’s not an obstacle. Similarly, you’ll want them to have the free time necessary to go diving. What good is a dive buddy that never has the time to go diving?

Do they have similar experience?

While you and your dive buddy can have different certification levels and even dive experience, it is something you want to consider. If you have a lot more diving experience and training, you’ll likely be taking on the role of the dive leader within the buddy team more often than not. You may also need to cater the diving you do to the experience level of your dive buddy. If your dive buddy isn’t comfortable with a certain type of dive because of their limited experience you need to keep that in mind. You never want to push them to do dives they may feel uncomfortable with.

On the flip side of the coin, if you’re the diver with less experience or a lower certification level, you need to communicate what you are comfortable with and not comfortable with. The plus side of being the less experienced diver is that you can learn a lot from a more experienced diver.

Do you have similar dive objectives?

What do you like to do on your dives? Do you like to take pictures, capture video, or maybe just relax on your dives? What kind of dives do you enjoy? Do you like shipwrecks or reefs? Do you prefer night diving or maybe drift dives? The point I’m trying to make is that you and your long-term buddy ideally should want to go on the same kind of dives and partake in similar activities during the dive. If your buddy is always taking their time in one spot to get that perfect macro shot of a nudibranch and you want to swim and see as much of a site as possible it can become a conflict and neither one of you will enjoy the dive.

Are they significantly larger or smaller than you?

Part of being a buddy is being able to render assistance if needed. If your buddy is much larger or smaller than you then it will affect your ability to be able to tow them if the need should ever arise. Also, different sized divers usually have different breathing rates. All things being equal, a petite 100-pound woman will have a much lower breathing rate than a large 250-pound man. Using different tanks can, of course, make it so that gas doesn’t cut the dive short for the smaller diver, but it is something to consider.

What kind of gear configuration does your buddy use?

An often-overlooked part of being a dive buddy is that the gear your dive buddy uses will affect your diving. If your buddy always uses a smaller tank than you, you might become frustrated by a buddy that is always calling the dive while you still have plenty of gas to continue diving.

Similarly, if you use a dive computer with a very conservative algorithm and your buddies dive computer is more liberal, that can also become an issue with the diving you want to do.

Sometimes there are major differences in gear. Maybe you dive a traditional single tank that is back mounted, and your buddy always dives sidemount. Perhaps your buddy uses a rebreather, that too can be a consideration that can affect the way each of you wants to dive.

Does your buddy dive Nitrox?

If you are doing deeper dives this is especially important. You and your buddy should have similar mixes on the dives you are doing. Otherwise, the dive profiles and no-decompression limits for the dives you’ll be doing might be different. If you normally dive with Nitrox so should your buddy.

Do you get along?

SCUBA diving is a social sport. You’ll be spending time with your diving buddy. You’ll need to plan your dives, possibly spend time on dive boats getting to and from the dive site. You might also drive together to the dives and maybe even spend time after the dive sharing a meal. That’s a lot of time with your dive buddy. You want to make sure this person is someone you generally get along with and that you enjoy spending your time with them.

Different Dive Buddies for different dives?

Sometimes you'll want to have different dive buddies for different activities. Maybe one dive buddies loves shipwrecks but doesn't really like going on reef dives. A different dive buddy loves going on reef dives but doesn't particularly like shipwrecks. You like doing both. There's nothing wrong with having different dive buddies for different dives.  

What are the responsibilities of a dive buddy?


Now that you know what a dive buddy is, where to find a dive buddy and what to look for in a good long-term dive buddy let’s discuss what your responsibilities are as a good dive buddy.

Pre-Dive

Before going on your dive, you’ll need to discuss several important elements of the dive you’re about to do with your buddy as well as perform some safety gear checks. You don’t want any surprises or confusion underwater, so this is when we clear everything up and get prepared for the dive to come. What follows are the minumum items to discuss and review with your dive buddy before every dive.

Getting to know a new buddy

If this will be your first-time diving with a new buddy there are several things you want to learn about them. First and foremost, you need to learn what their certification level and diving experience is. An advanced diver that’s only done 12 dives all of which have been part of a course is not the same as someone who’s been on a couple of hundred dives. You want to get a general feel for what their diving experience is so you can figure out who should lead the dive and also what your buddy may or may not be comfortable with.

Besides, understanding their experience you also want to know what hand signals they use for things like turning the dive, communicating air pressure, and emergency hand signals. Sometimes divers use different hand signals so it’s important to know how you and your buddy will communicate underwater. This is also a good time to ask if your buddy has a slate in case there is something you need to communicate underwater that can’t be expressed through hand signals. If you use a slate, you’ll want to let your buddy know that as well.

Another important topic that needs to be discussed with a new dive buddy is how to handle possible emergencies. These are some of the things you need to know:

  • Does your buddy give away their octopus for buddy breathing or do they donate their primary?
  • Where is the octopus on their dive rig?
  • Do they know how much ballast they need? (Ask)
  • How would you release their ballast in case of an emergency?
  • Do they have integrated weights on their BCD or are they using a weight belt?
  • How would you get them out of their gear in case of an emergency?
  • Does your buddy carry a Delayed Surface Marker Buoy (DSMB) and know how to use it?
  • What procedure do they follow in case of a lost buddy?

You want to know these things ahead of time, just in case the need arises.

Planning the dive

Now that you’ve gotten to know your dive buddy it’s time to plan the dive you’re about to go on. First, you need to communicate to your buddy what your objective is for the dive. If you plan to just relax and take in the sights let them know. If your dive plan is to take pictures or video, you need to let your buddy know this as well. Both you and your buddy must be on the same page regarding what you will be doing throughout the dive.

You and your buddy also need to decide on when you will turn the dive and how you will communicate that it’s time to turn the dive. Similarly, you should also discuss what your no-decompression limits are for the dive and how you plan to keep track of your limits. If you are using a dive computer, you might also want to discuss whether your computer is configured to be more liberal or conservative and how that may affect your bottom time.

This is also the time to decide on who will lead the dive. It’s best to have one person leading and the other following. If one diver has more experience with underwater navigation or simply has experience diving a particular dive site, they should be the leader. If you’re unsure as to who should be the leader because you both have similar experience than just pick a leader or take turns on different dives.

Finally, there might be special considerations your buddy needs to know before the dive. Maybe you take a long time to equalize your ears, or you prefer to extend your safety stops. Perhaps you know that you tend to breathe at a faster rate than most divers. If this is the case, you want your buddy to know before the dive so that there aren’t any surprises or any confusion during the dive.

The Buddy Check

Before going on the dive you’ll need to assemble your SCUBA gear and put it on. As you probably learned in your dive class this process should be done together with your buddy so that you can cross check eachother and make sure everything works properly.

Depending on the type of diving you are doing, you and your buddy may need to help each other to put on the SCUBA gear. If one buddy needs to lift the dive gear for the other buddy, the larger/stronger diver should put their gear on first. This is because they will need to hold the weight of their gear as well as the weight of their buddy’s gear for the longest amount of time while suiting up.

Once your dive gear is assembled and you’ve donned your gear, before entering the water you need to check your gear, as well as cross-check your buddies gear to make sure everything is in working order. This is also often referred to as a pre-dive buddy check.

At a minimum you should check the following:

  • Tank
    •  is the valve fully open?
  • Regulator
    • Does the first and second stage breathe properly?
    • Is the SPG working and showing that the tank is full?
    • Do you hear any hissing sounds that may indicate any sort of leaks?
  • BCD
    • Is the tank strap tight and holding the tank in securely?
    • Does the low-pressure inflator inflate and deflate properly?
    • If the BCD has integrated weights, are they in place and secure?
    • Does the BCD hold air when fully inflated? (make sure there are no leaks)
    • Are all buckles and straps secure?
  • Weight belt
    • If one is being used is it on securely and also is the buckle easily accessible in case it needs to be ditched?

Different instructors and dive agencies have their methodologies and even acronyms to facilitate doing a buddy check, so the above list is by no means comprehensive. There are many different ways of doing a buddy check in the diving industry, so follow whatever system your instructor taught you in your class!

Diving the Buddy System

Now comes what you’ve been planning and anticipating: The dive! The good news is that most of the hard work is done. By communicating with your buddy, having a dive plan, and doing the buddy checks you’ve gotten most of the work out of the way. There are still a few points however to keep in mind when diving with a buddy.

Maintaining the correct distance

The entire point of having a buddy is to have someone there to assist you should you need it. Your buddy acts as a safety diver for you, and you do the same for them. For this system to work you need to be within eyesight of each other. This will of course vary depending on the visibility, current, the topography of the dive site itself and whether you are diving at night or during the day. The main thing to keep in mind here is that should something suddenly occur such as an out of air emergency you should be no more than a few seconds swim from your buddy and you should notice it immediately.

In addition to staying within an appropriate distance from each other, you and your buddy should also maintain the same relative position throughout the dive. If you are diving to the left of your buddy, you should remain there for the entire dive. This way you each know in what general direction to look to find your buddy.

Dive the Plan

There’s a saying in diving. You plan the dive and then you dive the plan. Now it’s time to execute the dive plan. Because you discussed any objectives you have for the dive you can now execute those objectives. Maybe your buddy is taking photos so you can help find cool critters to photograph. Or perhaps your buddy would like to spear some lionfish so you’re on the lookout for them. The point here is that you and your buddy are a team working together underwater.

Also, because the dive has already been planned you know what your no-decompression time limits are, what your maximum depth should be throughout the dive, and when the dive will be turned. There are no surprises here.

The person who will lead the dive has been chosen before the dive so that buddy is responsible for navigating the wreck or reef.

Because hand signals and communication were established pre-dive you can now communicate with your buddy about things like your tank pressure, when to turn the dive, and any other relevant information.

When it comes time to ascend you know if your buddy will be doing a deep stop, how long they like to take on their safety stop and what their ascent rate is like (some divers like to come up slower than others).

Finally, because much of the dive has been planned out you’ve eliminated many of the things that can cause stress. You can now relax and enjoy the dive. This is why you’re here after all!

Post dive

One of the most neglected parts of the buddy system is the benefits it affords you after the dive. Just because you’ve successfully completed a dive doesn’t mean you and your buddy should go your separate ways. There are still several activities that great divers will do with their buddy’s post-dive.

Your gear still needs to be broken down, rinsed, and put away. Sharing in these duties with your buddy will make things easier, help to ensure you don’t forget anything and make carrying all the heavy gear less of a burden.

You should be keeping a logbook of your dives. Here, once again your buddy Is useful. By completing your logbooks together, you can compare notes. Did you think you had 70 feet of visibility or 90? What was the name of the site you did your second dive on? If you’re working on your diving performance, this is a good time to compare your Respiratory per minute volume or RMV. Who had a better breathing rate and why? How was your kicking technique, buoyancy, and trim during the dive?

You and your buddy can help coach each other so that you become better divers. What can you work on to make your next dive better? These are all things to discuss and document in your logbook so that you become a better diver each time you go diving.

Also, if you and your buddy were shooting photos or videos throughout the dive this is a good time to make copies of the photos or videos for each other.

How to Be a Good Dive Buddy

Dive buddy team on surface of the water

By following everything discussed in this article you will be a good dive buddy. These are some additional things you can do that will make diving with you even more enjoyable:

  • Move at the pace of the slowest diver. There’s nothing worse than having a buddy that is swimming at a pace that you feel you have to keep up with. Not only will both of you go through your gas supply faster than needed, but you’ll also likely miss out on some of the cool things to see on your dive. There’s no shame in being a slowpoke. SCUBA diving is supposed to be a relaxing sport!
  • Listen closely and take notes during the dive briefing. Two ears are better than one. It’s easy to miss some detail about the dive site or the dive in general. By listening closely and taking notes you ensure that if your buddy missed something you can fill them in.
  • Communicate early and often. Your air pressure, time left on your computer, and when you want to turn are all just examples of information that your buddy probably wants to know. There’s never any harm in communicating this information early and often. Also, if you are having issues such as equalization issues, feeling cold, tired, or even narced you don’t want these feelings to build up until they are unbearable before telling your buddy. The sooner you let them know the better. They may be feeling the same and decide to call the dive. Communication is key to being a good buddy.
  • Be on the lookout for equipment issues, even if they are small. Sometimes there’s a small leak coming from the SPG that wasn’t audible on the surface. Or perhaps your buddies fin strap looks like it’s about to break. Maybe a flashlight that’s in your buddies pocket accidentally turned on. These are all things your buddy should know about. The SPG hose probably needs replacing before the next dive, the flashlights batteries are being drained and might need recharging. Your buddy might need a new fin strap. These are all just examples of small equipment issues that sometimes aren’t noticed on the surface but become evident during the dive.

What about bad buddies? 

Unfortunately, sometimes you’ll come across someone who just isn’t a good buddy. Below are some signs that they may not be someone you want to have as a long-term dive buddy.

  • They constantly want to push things to the very limit. We all know the diver that gets back to the boat with barely any gas left in their tank. Or the diver that wants to say down until their computer shows that there is less than a minute left before they go into deco. If your buddy is constantly pushing the limits, they are not only putting themselves in harm's way, they may also be putting you into a dangerous situation.
  • They have very poor buoyancy, trim, and kicking techniques. They may even be one of those divers that inadvertently damages the reef because they are touching it due to their poor diving skills. If they are new and open to suggestions on how to become a better diver, it might be ok to continue diving with them. If, however, they are experienced and unwilling to work on becoming better, you might want to look elsewhere for a dive buddy. These divers also tend to suck through their gas supply very quickly!
  • They insist on being the dive leader no matter what! During the dive, you realize that they are not following the agreed dive plan and what’s worse, they have no idea of how to navigate the reef you are on. You might give them the benefit of the doubt, but eventually, you realize when the time comes to turn the dive that they have no idea what direction to swim in to return to the boat. Boat checks are now in order and if the visibility is poor or the currents aren’t cooperating you might have to do more than one before getting back to the boat. If this happens once or twice it might just be poor judgment. If it’s a pattern that’s a person you probably shouldn’t dive with.
  • You just don’t get along. There are a million reasons why some people might just not get along. Diving is supposed to be fun. If the person you’re diving with isn’t pleasant to be around you might be better off finding another dive buddy.

What About Solo Diving?

With all that is required for buddy diving, you might be wondering if it might just be easier to do solo diving. Some agencies in the diving industry have even created a certification for solo diving. While solo diving has pros and cons which are way beyond the scope of this article it’s important to know that many dive operations will not allow you to solo dive. Because solo-diving requires you to have completely redundant systems in case of an emergency and a much higher level of training, some even consider it to be a form of technical diving.

One other drawback to solo diving is that you simply do not have someone to share the diving experience with. Diving is more fun when it’s shared with someone.

Conclusion

At the end of the day being someone’s dive buddy is a type of relationship, even if it’s just for a dive. It’s important that you pick someone you are compatible with, that you know is competent and that you will enjoy your diving with. Having the right dive buddy makes diving safer and more fun!

You also want to be the kind of diver that others want to pair up with. So knowing and using the buddy system is critical to attracting the right kind of buddies.

What do you look for in a dive buddy? Is there something we missed? Let us know in the comments below.

Scuba Tank

Aluminum vs. Steel tanks: How Heavy is that SCUBA Tank?

By Jose Cernuda

What 2 metals are SCUBA tanks made of, Aluminum vs. Steel tanks, How heavy is a SCUBA tank

What kind of tank do you use when you go diving?  The size of the tank and whether it's made out of steel vs. aluminum will hugely influence how much weight you'll need to take with you on your dive.   Many divers think diving with one type of tank is better than diving with another.  The truth is that the type of diving you do, where you are diving and even the thickness and type of exposure protection you use can play a part in your choice of SCUBA cylinder.

In another post, we talked about the importance of buoyancy checks and determining exactly how much weight you need in order to make your body neutral underwater.  Besides your body and your gear, you have to compensate for your SCUBA tank as you dive.

What 2 metals are SCUBA tanks made of?

Aluminum Vs. Steel Tanks

You may be asking ” how heavy is a SCUBA tank,” but the real question is how buoyant it is.  Different tanks have different buoyancy characteristics.  As divers we need to be aware of the buoyancy characteristics of the tanks we use when we dive.  This is important because it determines how much weight we need when we go diving.  It is also good to know because we can use tanks to replace ballast depending on our weighting needs and diving conditions

There are two types of SCUBA tanks for divers to choose from.  Aluminum SCUBA tanks tend to be negatively buoyant at the start of your dive when they are full.  However, as you dive, these tanks tend to become neutral and can even be positively buoyant by the end of your dive. Because of this, you have to consider the tank’s positive buoyancy at the end of your dive when determining how much weight you will need.  

Both steel and aluminum SCUBA tank sizes vary.  Different tank sizes have different buoyancy characteristics.  For example, a steel 120 SCUBA tank will have different buoyancy characteristics than a steel 80 SCUBA tank.  Not only do sizes affect their characteristics, whether it is a high pressure SCUBA tank or a low pressure SCUBA tank makes a difference and so does the tank manufacturer. Faber tanks specs are not the same as Catalina or Luxfer tanks.  It is important to research these differences when choosing your tanks.

Steel SCUBA tanks tend to be negatively buoyant throughout your dive.  So when diving with steel tanks, you will not need the same amount of weight.  It is important to keep in mind that the buoyancy characteristics of steel tanks also change throughout a dive.  So while a steel tank might be very negative at the start of a dive, it can become closer to neutral as you dive.

We did a quick video below to illustrate the point. It’s a cool little experiment you can try with different cylinders and see what the buoyancy characteristics are.

What cylinder do you dive with and why?  Please feel free to comment below, we would love to hear from you!

Scuba Diver removes her mask underwater

Increasing your comfort underwater: One little-known drill that boosts your confidence like crazy!

By Jose Cernuda

Scuba Diver removes her mask underwater

You’re on a dive in 65 feet (that’s about 30 meters for my non-American friends) and your regulator begins to free flow. What you do next could be the difference between a cools story and a trip to a hyperbaric chamber

 

Without going into what the proper procedure would be (I’ll leave that to the training agencies) how comfortable would do you think you’d be with this situation? Unless it’s something that you feel would be a minor annoyance, you might want to read on to learn a simple drill you could do to help you deal with this potentially dangerous situation.

One of the most important attributes you can have as a diver is to be both comfortable and confident while underwater. Unfortunately, this is one of the toughest things to “teach” in a rushed SCUBA course.  There really are two reasons why this particular situation is hard to teach.  First, most dive courses barely have enough time to cover the basics, much less deal with events like these.  Second, being that this is a situation that is much more about mental state than anything else, it is hard to mimic.

One of the best ways that I have seen my students become comfortable underwater over the years is by mastering skills which require them to hold their breath. The reason why breath-held skills increase your comfort on SCUBA is simple, if you know you can handle tasks which require you not to breathe for more than a few seconds, then any situation which can happen on a SCUBA unit becomes trivial because, for the most part, you’ll always have air when you’re on SCUBA. Even in the event of a worst case scenario, an out of air situation, you’ll still know you have plenty of time to figure out what to do and execute it so you can come out virtually unscathed.

The Skin Diving Bailout

So, just what is a Skin Diving Bailout anyway?  The skill is actually quite simple to complete and does not require SCUBA gear.   This skill should be done in shallow water, 4 or 5 feet (1.5 meters) is plenty.

A skin diving bail out is when you immerse yourself into the water with your mask and fins off. You can wear a weight belt for this skill, just make sure you do a buoyancy check and are properly weighted.

  • You begin by sitting on the edge of the pool with your mask and fins in your hands.
  • You then immerse yourself into the water while holding your breath.
  • Once you are underwater, you place your fins on your feet.
  • Then you put your mask on and clear it,
  • After your mask is clear, you come to the surface and blast your snorkel. You should be able to continue breathing through your snorkel at the end of the skin diving bail out while keeping your head in the water.

The key to mastering this skill is to take your time doing it. Make sure you breathe slowly and deeply before jumping in the water. Take a deep breath just before you jump in the water. 

Now stay calm! Slowly put your fins on, put your mask on, clear it and finally clear your snorkel.    Staying calm and taking your time is key!  You’ll be amazed at how much easier it is to complete this skill when you take your time.  Rushing usually will just make you feel anxious and have you run out of air much sooner.  Be deliberate in your movements.  When it comes to this skill, fast is slow!

This is the real takeaway, whatever happens underwater can be handled.  The key is staying calm, and acting slowly and deliberately.  Watch the video below to see how I do a skin diving bail out.

Have you ever done a skin diving bail before? If so, what was your experience with it? I’d love to know in the comments below.

scuba diver being Neutral underwater

Are you over-weighted too? How much weight do I need for scuba diving?

By Jose Cernuda

SCUBA diving buoyancy control, How much weight do I need for scuba diving, Dive weightsHow much weight do you use when you go diving?

If you're anything like me when I first started diving it's probably too much!

When I first started SCUBA diving, I did not know I was over-weighted.  It had never really dawned on me to check how much weight I needed.  I was trained with 12 pounds of lead and that is what I dove with.  That is until I got to my Instructor Training Program.  My instructor stripped me down to four pounds and proceeded to tell me that I was diving with way more weight than I would ever need, although he was not so nice about it.  Needless to say, I felt a little silly on that day.  I wish someone would have told me something prior to sitting in a pool with a seasoned instructor trainer…I was red-faced with embarrassment on that day!

How much weight are you taking with you when you dive? Are you sure this is the right amount? If you’re not 100 percent sure that you’re using the correct weight, then you need to read on.

The only way to properly determine how much weight you need in the water is to perform a buoyancy check.  A SCUBA diving buoyancy calculator may be a good idea in theory, but you will only know the right amount of weight by getting in the water and checking yourself.  A buoyancy check is when you place yourself in the water and, through trial and error, find the right amount of weight which you need to SCUBA dive.             

Having the correct amount of weight to act as ballast is super important. If you have too little weight, you will float towards the surface, especially at the end of the dive when your cylinder is lower on gas. If you have too much weight, you will work harder, possibly have your body in a poor position in the water column, and could even place yourself in a potentially dangerous situation.              

The goal of being properly weighted is to end your dive perfectly neutral when you are at your reserve pressure, with little to no air in your BCD.              

If you still need air in your scuba diving buoyancy control device (BCD) when you are at the reserve pressure at the end of the dive you need to ask yourself why? This extra weight simply caused you to exert more energy throughout the entire dive and likely caused your breathing rate to go be higher than it needed to be.               

Before I begin to explain how you can perform a buoyancy check, you have to understand what can affect your buoyancy. 

Some of the things that can affect buoyancy are:

The Density of the Water.

  • Salt water is denser than fresh water. This means you will need more lead in salt water than you will in fresh water.

Your Dive Gear

  • Your regulator, BCD, fins, etc. all have weight associated to them which can affect your buoyancy.
  • Depending on the cylinder you are using, you may need to add weight to offset for the cylinder being low on gas at the end of the dive.
    • This is one of the trickiest factors to consider. The reason why is because a cylinder may be negative and sink at the beginning of the dive, but positive and float at the end of the dive when it is near empty. You have to consider that the compressed gas in the cylinder has weight too. This video below shows you a simple experiment I conducted to illustrate the point.

 


Exposure protection

  • If you are wearing a neoprene wetsuit the neoprene is positively buoyant. Depending on the thickness of the suit and your body size, you will need to offset the buoyancy of the wetsuit.
  • If you are diving with a drysuit, you will also need to offset for the buoyancy created by the drysuit. Depending on what undergarments you are using and the material of the suit itself, you will need to add lead to offset the buoyancy created by the suit and the undergarments.  I would like to mention that drysuit diving should not be attempted without taking a specialty course as it has a large learning curve when compared to diving in a wetsuit

Body composition

  • Muscle is denser than water, so it tends to sink. I have had many students in the past who lifted weights and were very muscular and lean, these students often needed little or no extra weight to stay underwater
  • Fat is less dense than water, so it tends to float. If you have more body fat, you will probably need more lead to offset the positive buoyancy caused by the fat.
  • Lung volume; everybody’s lungs are different. Because we are breathing while underwater, this is the one variable that is constantly changing, however, a bigger lung will have more air in it than a smaller one and hence require a little extra lead.

Because of all of these variables, especially the ones dealing with your body composition. The only way to figure out how much weight you will need when diving is to perform the buoyancy check.

The way I like to perform a buoyancy check is wearing whatever I will be using for exposure protection (i.e. wetsuit or drysuit) and in the same type of water I will be diving in (If you will be diving in the ocean, you need to do this in salt water, the amount of weight you use in a pool will be different than what you might use in the ocean).  

I like doing the buoyancy check for just my body, and then a separate buoyancy check for just the gear. There are two reasons why I like doing it this way.  First, it is easier in my opinion to balance in the water and find the right amount of weight for just yourself.  Second, I tend to dive different gear configurations and different cylinders for different purposes.  By separating the amount of weight I need for myself from the weight I need for my gear, I am able to easily adapt for different cylinders and gear.  If you dive with different gear configurations, you may want to consider doing the same thing.

So how do you perform a buoyancy check? Below are the steps as well as a video showing you how to do a buoyancy check.

  • Step 1: Standing in water that is about neck deep. Take a weight of about 2 pounds (1 kg) and hold it behind your back.
  • Step 2: Focus on your breathing for a moment. Now take a breath that’s about seventy percent of the total volume of air you think you could fill in your lungs (don’t worry too much about an exact amount, it’s probably impossible to determine what exactly 70% is, just use your best judgment)
  • Step 3: Now slowly ease yourself into the water. You want to go really slow to prevent yourself from bobbing up and down if you float.
  • Step 4: Make a note of where you are in respect to the water level and your head.
    •  If you sink, underwater, you will need to try with less weight, or maybe even no weight.
    • If the water level was below your forehead (your eyes as an example) you will need more weight.
    • Repeat this exercise with more weight until you find the correct amount of weight that is needed to be right at forehead level.
  • Step 5:  Once you find the correct amount of weight, make a note of it.  This is how much weight you need to be neutral in the water without scuba equipment on.  If you know how much weight you need for the scuba equipment, and your cylinder at reserve pressure then add these two numbers together and you will know the total weight you need in the water.

 

 

Once I know how much weight I need for myself, it’s now time to do the same for my gear. The gear is actually a bit simpler since there is no balancing required on your part.

The steps to doing a buoyancy check for your gear are as follows:

  • Step 1: Drain your cylinder to its reserve pressure (i.e. 500 PSI or 50 Bar)
  • Step 2: Start with 1 pound (1/2 kilo) and place it in your BCD’s pocket or attach it with a string if your BCD has no pockets.
  • Step 3: Notice if your Scuba Rig sinks of floats. If it floats, add more weight until you can get the rig to be just neutral or ever so slightly negative. If it sinks with no weight added to it whatsoever then you do not need any weight to compensate for your rig’s buoyancy.

 

Putting it all together

Once you know the amount of weight that you need for yourself and the amount of weight that you need for your rig, all that is needed is to add the two numbers together to arrive at how much weight you should be carrying into the water.

Always keep in mind that the number you arrive at will change if you change cylinder types, exposure protection, move from salt to fresh water, or if you gain or lose weight yourself. Also, the amount of weight you arrive at with a buoyancy check is not a number set in stone it is simply a best starting point. Once you start diving, you may notice that you can actually use less weight, or maybe that you’ll need slightly more. If you decide to add or eliminate weight do so very slowly. Your goal should always be to be neutrally buoyant with no air in your BCD at the end of your dive with the cylinder at its reserve pressure.

How much weight are you using when you dive, and what type of exposure protection and rig are you using?  Let me know in the comments below.

Scuba Diving Flutter Kick in Pool

Swimming Like A Fish: How to Master the art of SCUBA Kicks

By Jose Cernuda

 Scuba Diving Flutter Kick in PoolWhat’s your go to kick when you’re diving?  Why?  Whenever I ask this question, most people don’t really have an answer as to why they use the kick that they do.

Just as important, many times the kicking technique is less than efficient.  In this article, I want to show you the two most common kicks in scuba diving, when to use each one and demonstrate how to perform each kick efficiently.

SCUBA Kicks

The two main kicks used when scuba diving are the flutter kick and the frog kick. The flutter kick is the scissor-like kick which is similar to the kick you would do if you were swimming freestyle. This is the kick most people instinctively do when they first start scuba diving and snorkeling. The frog kick is the kick which resembles the kick used when completing the breast stroke. It’s named the frog kick because it resembles a frog kicking underwater.

These two kicks are go-to kicks used when scuba diving. What many people do not realize is that they have two distinct purposes and should be used accordingly. In the video below I describe the two kicks and when to use each one.

Before going into the kicks themselves, it’s important that you understand some general principles that will make any kick you use underwater more efficient.

  • First, you want to make sure you make yourself neutral in the water.  The kick should only be used to move your body horizontally in the water column.  If you are kicking to stay off the bottom, then you are wasting energy.  IN order to be efficient, you must be neutrally buoyant.
  • Second, you need to get used being in a horizontal position. This position will eliminate drag in the water and help you move to where you want to go without wasting energy.
  • Next, you need to understand that your hands are not needed to propel yourself underwater. Your hands should be either by your side, or crossed or someone where near your body where they are not causing drag in the water.  Using your hands to try to move through the water is extremely inefficient
  • Finally, you need to know which kick to use and when.

The Flutter Kick

The flutter kick is a power kick. It is the kick you should use when you need to either move rapidly or move powerfully because of a strong current. Because it is a power kick, it is also the kick which consumes the most amount of gas. This is because the flutter kick has no resting phase. When you are flutter kicking, you are basically constantly moving.

The key to an efficient flutter kick is to keep your feet relatively straight, your toes pointed, your ankles loose and let the power come from your hips. You can see in the video below how I demonstrate this kick.

 

The Frog Kick

The frog kick is the more efficient of the two kicks presented here. It’s the kick you should be doing most of the time.

The frog kick has a built in resting phase. That is to say, once you kick you get to rest and recover while you are gliding forward. Because of this, you’ll consume less gas while diving using a frog kick. The video below describes and shows how to do an efficient frog kick.    

The key to both of these kicks is knowing when to use each one, and to practice them both until you have mastered them. 

One huge help in getting your kicks right is to use an underwater camera to see how you look while you are diving. Many people are surprised to see both what their kicking technique looks like, and what their body position is like. Cameras like the GoPro make it relatively inexpensive to see what you look like in the water.

I’m curious to know, what kick are you using most of the time and why? Let me know in the comments below.