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Tuesday, 11 March 2014

Buoyancy Basics Part 3: Buoyancy Control Devices

When you are Scuba Diving, it should not feel like you are exerting yourself. If diving feels strenuous, you are generally doing something wrong somewhere. Most experienced Divers (not the ones pushing the boundaries of scuba who can experience stress but for very different reasons) will tell you that diving should be a relaxing, easy past time... and they are right.



Perfecting your Buoyancy Skills is the best way to make your diving strain free and now we understand the basic principles behind buoyancy, we can look at what we can do to make our diving better by improving this core skill.

There are a number of things that affect buoyancy and we have previously discussed weighting for scuba diving and, hand in hand with weighting is use of your Buoyancy Control Device (BC).

halcyon single tank wing with harness

Whether you dive in a wetsuit or a drysuit, your primary means of buoyancy control should be your BCD or Wing, which makes this piece of diving equipment crucial to perfect buoyancy control and having the correct BC for the diving you do is essential.

So, a BC (whether jacket style, wing or sidemount BC) is basically a bladder to which you can add or subtract air to control your position in the water column. It will have some means of actually adding the air and this is usually through a low pressure system, allowing you to add air from the cylinder, while dump valves are used to release air, alongside an Over Pressure Release Valve (OPRV) to prevent over filling.

The BC must have sufficient lift capacity to hold the diver and full kit at the surface with their head comfortably above the water line...Just as a note to this, if your BC will not hold you at the surface but you have 20kgs of lead on your weightbelt, drop some lead before you go out and buy a bigger BC... you have overweighted yourself and this will cause problems both at the surface and in the water...

Before any dive, you should check your BCD is working correctly by connecting it up to the cylinder and inflating it fully until the OPRV kicks in. Then check all the dump valves to make sure nothing sticks open or closed.

On the dive, you should add air in small amounts on the descent.

As we descend, the increasing water pressure causes the air we put into our BC to compress and we need
to add more air to equalise it to the ambient pressure.

diver lets air out of his bc by holding the deflator above his head and pushing the deflate buttonEqually, as we ascend, the decreasing water pressure causes the air in our BC to expand and we need to release some. Again, this release of air should be in small amounts and you should ensure that the valve you are using to subtract the air from the BC is the highest point in the water, as air rises.

If you are using the Over the Shoulder Inflator/Deflator, you must hold this up above your head and come into a more head up position in the water. If you are an advocate of the kidney dump to stay in trim, you must roll slightly to make the kidney dump the highest point in the water.

It is important that you know how to operate the BC and know where all the controls are without having to fumble, so you can make a speedy adjustment, if needed. This is where a check dive can be invaluable if you are hiring equipment and getting advice from someone who knows what they are talking about is second to none when buying your own kit.

BCs are pretty standard for a reason. They work! Variations are quite often just gimmicky sales pitches that are more likely to hinder than help and with a piece of Diving Equipment that is so central to the core Diving skills, it is important to get a BCD that works for the Diving you will do.

scuba diver with jacket style BC and instructor using diving wing