Buoyancy control with drysuit

[flots am]

I am taking the PADI drysuit class to learn how to dive in my new drysuit. My instructor says to only add air to the suit to avoid suit squeeze and use the BCD for buoyancy control but PADI says the opposite! Who is correct and why?

They're both wrong.

If you start with a nearly empty tank then add just enough weight to make you neutral with just enough air in the suit to eliminate squeeze, you'll be just right and (probably) won't have to add any air to the suit or BC. Keeping enough gas in the suit to eliminate suit squeeze will also keep you neutral.

This should work nicely unless you're carrying a lot of gas, in which case, there's no way to avoid being significantly over-weighted at the start of the dive. In that case you can use your BC for buoyancy control.

No matter what you do, I'd avoid adding a lot of gas to the drysuit since it tends to move around a lot, making good trim more difficult. It also tends to vent by itself, leading to increased gas consumption.

flots.

 

[Ben Prusinski]

Ok I will experiment and find what works best for me.

 

[Edward3c]

Both methods work.

Just remember if you use both you have two air spaces to control whenever you ascend.


From 30m to 10m the little you've put in the suit will have doubled in volume. I've seen a number of uncontrolled ascents because of diving this configuration where the diver forgot to vent the suit. Normally happens when the diver is overweighted, even on an empty cylinder. Hence my preference to having a constant volume valve (auto dump) rather than a cuff dump.


Flots's suggestion is the way we (BSAC) teach weighting. Part of the training for each grade is demonstrating neutral buoyancy in 1.5m. Its interesting that new divers (Ocean Diver) can do it easily, but more experienced (Dive Leader and Advanced Diver) are often overweighted.


Kind regards

---------- Post added April 5th, 2013 at 05:21 PM ----------

I was reminded of this today.

If your training has covered rescue of another diver you will have to control both your suit and BC in addition to the casualty's buoyancy. Whereas if you only use the suit its one less air space to manage.

Kind regards