Everything Buoyancy

Buoyancy is part of the fundamentals of SCUBA Diving and achieving proper buoyancy can usually turn a not so fantastic dive into the greatest dive that you have ever had and vice versa.

So how do you master buoyancy? Simply put the more you dive the more you understand how to compensate for your own movements underwater and where to assign and place certain gear, such as your cylinder and BCD. But that is not to say that we can’t give you a few tips and tricks on how to manage and improve your own buoyancy without an instructor to guide you.

Let’s talk about what buoyancy is first, Buoyancy is referred to the upwards thrust or force exerted by a fluid that opposes the weight of an object which is either partially or fully submersed in a liquid. Thus, the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object.

According to Archimedes’ Principle the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces.

The weight of the displaced fluid is directly proportional to the volume of the displaced fluid (if the surrounding fluid is of uniform density). In simple terms, the principle states that the buoyancy force on an object is equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume times the gravitational acceleration, g. Thus, among completely submerged objects with equal masses, objects with greater volume have greater buoyancy. This is also known as upthrust.

Now that we understand the basics of buoyancy and how it is affected by different objects and their volume, lets investigate how you can improve your own buoyancy in SCUBA Diving, it Is also important to note that there are 6 factors that can affect your buoyancy.

• Ballast Weight
• BCD Inflation
• Trim
• Exposure Suit
• Depth
• Breath Control

 

• Proper Weighting

Being properly weighted can make or break your dive, you can either battle to stay underwater or you may need to overinflate your BCD to help keep you off the reef.

How do you calculate the amount of lead needed for you? To check your weight gear up as per normal with a near empty Cylinder (50bar or less), start by inflating your BC, once ready take a normal breath of air and hold your breath, as you hold your breath deflate your BCD entirely and you should float at eye level.

A few key Aspects to remember, when transitioning from fresh water to salt water it is always a good idea to add 2kg extra due to the nature of salt water being more dense than fresh water, same when diving with Aluminium and Steel Cylinders. Steel cylinders are less buoyant than Aluminium Cylinders and thus would require 1kg – 2kg less when diving with Steel Cylinders. A thicker or thinner exposure suit also plays a vital role in how much weight is needed to be properly weighted and whenever you use a different suit it is advised to do a weight check before your dive or at the very least maintain a log of how much weight you used with what thickness of exposure suit.

• Body Positioning

Being streamlined can drastically change your buoyancy factors due to how you are swimming in the water and can reduce air consumption but more on this in a later blog.

Proper body position is referred to being horizontal with your knees slightly bent, in this position when swimming you are swimming in a straight line and not swimming up or down. By swimming up or down you are changing the nature of the air inside your BC and the compression factor on your exposure suit, thus it may feel you are either too light or too heavy.

You can improve you own body position by swimming around a grid hanging in mid water and noting if you are swimming in a head up or head down position, once you have established your swimming position the next step is to adjust your lead and positioning of your lead accordingly.

Swimming in a head up position generally refers to being overweighted and swimming in a head down position generally refers to being underweighted.

• Short Inflations

Buoyancy is a slow process, and you may not notice an immediate difference when adding air to your BCD, but refrain yourself from holding down the inflator as this may cause a runaway ascent.

Instead do 1 – 2 short bursts and take 2 – 3 breaths to allow the newly added air to seat and work its magic. If you notice that you are still slightly to negatively buoyant add another 1 – 2 short bursts and wait to see if there are any changes.

Being neutrally buoyant does not refer to you being stationary mid water but refers to rather moving up and down in a gentle fashion while breathing in a clam and relaxing way.

• Breath Control

Your lungs are natural BCD’s and thus just by taking a breath you can affect your buoyancy in such a way that you can effortlessly glide up and over obstacles without the need of inflating or deflating your BCD or even without the effort of changing your body position to swim up or down over the obstacle.

By taking a deep breath you can increase your own buoyancy and by exhaling forcefully you can decrease your own buoyancy by a factor of 1kg – 2kg.

With this being said it is important to note that breathing normally and in a relaxing way you should be neutrally buoyant at your given depth.

• Take a Course

It is possibly to achieve proper buoyancy on your own, however not knowing how to achieve buoyancy may negatively affect your diving as well as you may learn improper technique. It is for this vary reason that PADI has implemented the Peak Performance Buoyancy course where you will work with an Instructor who may help and perfect your buoyancy.

Doing a course is highly advised as you will be able to comfortably and safely be able to experiment with multiple techniques and adjustments whilst under the direct supervision of a professional in a safe and controlled environment.

• Practice

Although the theory is important, the best way to achieve perfect buoyancy control is through practice. Dive often, always be aware of your body and your surrounding, use proper techniques, try to perform your basic open water skills while maintaining neutral buoyancy and good trim, experiment with different buoyancy exercises, but most importantly enjoy your dives and stay safe.