Scuba Diving Buoyancy Control

Updated March 26, 2024

Control of buoyancy is one of the key skills to master for a diver to be comfortable and confident. Yet for new divers, it can be a major hurdle to overcome. In this article, some of the principles and aspects of buoyancy control are described and tips offered to make progress a little faster and easier.

Buoyancy

When you are on the surface you would like to be positively buoyant, like a boat floating, rather than a rock that sinks. The larger boat displaces water that weighs more than the boat, so it is positively buoyant. The smaller rock displaces water that weighs less than the rock, so it is negatively buoyant. At depth, your goal is to be neutrally buoyant, with your body and equipment displacing water that weighs the same as your body and equipment.

What Difference Does Buoyancy Control Make?

When you are neutrally buoyant you are able to maintain a position in the water neither sinking nor floating.

It is a more relaxing position. Little effort needs to be exerted resulting in less air consumption and fatigue.
The environment is safer from you crashing into it or finning it and creating damage to the reef.
You are safer from the scrapes, scratches, and cuts from crashing into the reef and more importantly, you will have better control of ascents and avoid decompression sickness and air embolisms that can happen from going up too fast.
Your confidence, sense of well-being, and ability to relax and enjoy the experience are enhanced.

How to Achieve Great Scuba Diving Buoyancy Control

Weighting

Carrying the proper amount of weight is essential to achieve proper buoyancy. If you are too heavy, you will feel the need to compensate by adding air to your BCD. Here is a way to measure your buoyancy level. If you have an empty tank and no air in your BCD at the surface, you should be at eye level with the water when you are wearing the correct amount of weight. When you are at a 5 meter (15 foot) safety stop your air will be significantly depleted leaving your tank positively buoyant. In making adjustments to your weighting make it in small increments of .5-1 kg (1-2 pounds). Also, keep in mind the thickness of your wetsuit will have an impact. It will become more buoyant on the ascent and at the surface. Keep a record of the amount of weight you use in your log to help gauge any adjustments.

Breathing

The air you carry in your lungs can add significantly to buoyancy. With your lungs alone you can adjust your position in the water column. If you want to ascend a few feet you can inhale a little more than usual, and the vice versa also is true. By exhaling a little more than you normally do, you can descend a bit. After making your move you should return to normal breathing and never hold your breath.

Use of the BCD

When you are on the surface the BCD should be inflated enough to be positively buoyant and comfortable. To descend you should deflate slowly and descend to depth becoming neutrally buoyant. The goal is not to need to make further adjustments from there. With correct weighting, there may be no need for it. Beginning divers often seem to have the idea that the BCD is an elevator. To ascend they add air and when they want to descend they release air. It should not often be necessary to add and release air. When you do feel the need, do it in small increments which will aid in maintaining control. If you find you want to release that last bit of air, stretch the inflator hose above your head and lower your right shoulder allowing any remaining air to flow to the highest point. Simultaneously you could also use your right arm to squeeze the BCD against your chest to push out the last few bubbles. Otherwise, from a horizontal position, the dump valve at the bottom on the back may be effective in releasing that last bit of air. For some tips on selecting a BCD, please check out my buying guide: BCD Buying Guide

Trim

Trim refers to the diver’s horizontal position in the water. Good trim is completely flat and steady with the knees bent at a 90-degree angle. This is the most streamlined position for a diver with the least surface area while progressing forward. It enables the smallest amount of exertion to be efficient with less fatigue aiding in buoyancy control. Good placement of weights can assist. With a weight belt, the weights should be divided equally around your hips. Using an integrated system the placing of equal amounts of weight in the right and left pockets can achieve the same effect. Some BCDs are designed for you to place weights on each side of the Velcro that secures the tank which offers the same chance for balance.

This video shows a technical diver demonstrating excellent trim.

Two Final Steps to Achieve Scuba Diving Buoyancy Control

Take a Class

After the open water diver class, most diver training agencies offer continuing education specifically related to improving buoyancy control. SDI offers the Advanced Buoyancy course. For PADI it is the Peak Performance Buoyancy specialty course. The SSI course is called Perfect Buoyancy. The three are very similar and provide focused instruction to address any issues related to buoyancy.

Practice in Shallow Water

Mistakes in shallow water are more forgiving safety-wise but small changes in performance can have a big effect on buoyancy. If you can master buoyancy in shallow water it transfers over to other depths pretty well. Imagine yourself as the technical diver in the trim video up above.

Feedback and Comments

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