Buoyancy control is the single biggest cause of in-water incidents. For some time, an interesting culture within K&E with regards to buoyancy control has existed. Whilst there is no right or wrong way, there are ways that are tried and tested and therefore recommended, especially for new divers (say, less than 200 dives).
You should feel free to develop your own preferred method of buoyancy when you have gained experience, but if you are teaching someone else or are relatively new to the sport yourself, then doing it the recommended way would seem infinitely sensible.
This article looks at why using your dry suit (if you have one) and not your BCD is the recommended method of buoyancy control during a dive. It also covers how to perform a weight check and make your diving as safe as possible.
There will be those who protest and claim their way to be best. Please note, this article does not represent just my views but the views of many very experience divers and instructors who have developed techniques over many years and have taken issues such as a detailed analysis of the accident statistics into account. Technical divers who carry four cylinders or more fall outside of the normal rules and often have to dive in a different manner due to the weight of equipment they are carrying, that doesn’t mean that their method is the best way for the rest of us.
## Method of Buoyancy
The simpler the means of controlling your buoyancy, the better. If things go wrong you do not want to have to think, you want to be able to instinctively react, keeping things simple helps you do this.
The BSAC instructor manual states:
> In general, the objective should be to keep the task of buoyancy control as simple as possible by using the minimum number of volumes of diving gas.In practical terms this means that where students wear no protective clothing or wear wet suits, buoyancy control is effected using the BC. Where dry suits are worn, buoyancy control is effected using the diving gas in the suit.
For lesson OO1 it says:
> …Adjust buoyancy as depth changes **using dry suit inflation / venting** in small bursts…
Where wet suits are worn the recommendation is different of course:
> …The only adaptation to the lesson content is that buoyancy control will be by the use of a BC rather than by dry suit inflation..
*Note that this same recommendation is given in “Safe Diving Practices” – the bible of BSAC recommendations.*
If your weight is correct (see below) then the gas in your dry suit is adjusted by you throughout the dive to maintain neutral buoyancy. The additional weight carried at the beginning of a dive due to having a full single diving cylinder (approx 2kg) is compensated for by an additional 2 litres of gas in your dry suit (easily accommodated). Any gas in your BCD is therefore above and beyond that required and indicates you are most likely over-weighted.
## Weight Check
If you are weighted correctly then you will not have unnecessary buoyancy gas. With less gas to migrate, you will be more stable in the water. The smallest possible volume of gas means the smallest buoyancy change as a result of a change in depth, buoyancy is therefore more controllable. Getting your weight right is therefore important.
Buoyancy devices primarily provide support on the surface at the beginning and end of your dive making those parts safe. You should have enough weight on your weight belt to achieve neutral buoyancy with an empty cylinder.
A buoyancy check is best done with cylinders with approx 50 bar in. Remove all air from your BCD on the surface and all air from your dry suit (without causing uncomfortable suit squeeze). With your lungs full of gas, you should float at about nose level in the water, as you breath out you should slowly sink. Add 0.5kg of weight to allow for the reserve gas in a single cylinder and that is your weight sorted. If you do a check with a full cylinder simply add more weight to compensate accordingly. The instructor manual recommends a similar method:
> …In approximately 2m of water all the air should be vented from the dry suit and “mid water hover” boyancy check should be carried out with low cylinder breathing gas contents (approximately 50 bar)…