Buoyancy Control in a Drysuit

Question
Hi Mike! Please address the apparent divergence of opinion
amongst very experienced divers (instructors, et. al.) as to whether the drysuit should be the primary means of BC while submerged vs. continuing to use the BCD as usual and inflating the drysuit only to ease compression. Thanks!!

Answer
Hi Tom

Wow...you ask a loaded question!!  There are valid opinions on both sides of this question so my input won't tip the balance either way.

It is my personal opinion that buoyancy should be controlled primarily by the use of air in the dry suit.  HOWEVER...in order to effectively do that, proper weighting is critical.  If weighting is correct, it takes very little air to change buoyancy.  This air will be distributed fairly equally throughout the suit.  One potential problem with using the drysuit to control buoyancy is that, during a dive, the BCD harness compresses the area around the torso and chest, forcing air to the extremities.  If properly weighted, this will be a small amount of air and the diver should remain stabilized.  If the weighting is too much, then it takes a larger amount of air to control buoyancy and this air may shift to the extremities in an unbalanced manner, causing stability problems.  Using air in the BCD to control buoyancy keeps all the air in the region of the torso and can help prevent stability problems.  However, having the inflated BCD over a partially inflated drysuit can present problems in trying to keep the BCD from shifting during a dive.

You must, of course, use some air in the drysuit to avoid compression so trying to balance air in both the drysuit and the BCD adds unnecessarily to task loading during the dive.  I like to keep things as simple as possible so I'd prefer to  do all my air adjusting through one valve!

So, to summarize, I favor using drysuit air to control buoyancy IF the diver is properly weighted to start with.  This also reserves the lift capacity of the BCD for emergency flotation should the drysuit fail.

Tom, I'm sure this doesn't resolve the issue of buoyancy control in a drysuit but now you've got my two-cents worth...hope it helps!!

I wish you warm diving!

Mike Giles
Mike's Dive Center
mikescuba.com