Drysuit use and buoyancy

[pointy]

 

[jale]

key point is "primary"
DS is not a "primary" buoyancy device but of course it is still a buoyancy device and anyway, if you are properly weighted with a balanced rig, all of this is not really a problem

 

[pointy]

The authors of the video make false claims to convince us that it's a bad idea to use your suit for buoyancy control:

He says that you will have air leaking out of your suit at the neck causing you to lose control of buoyancy. Sure, sometimes a bit of air might burp out around the neck (with some suits) but I've never found that to present a buoyancy problem.

He said extra air in the length of the suit will make it difficult to maintain good trim. Actually, trim is easily controlled by shifting your posture to get the air where you want it.

He also says that air in the suit can only migrate slowly towards the shoulder dump valve. That is never a problem. With a little practice it's easy to move the air through the suit for efficient venting, or to keep the air in the suit when necessary.

Why would anyone want to carry enough lead to stay submerged with air in the BC? You could put that extra air to good use by carrying it inside the suit where it might help to keep you warm.

 

[GJC]

I tried both ways. With a single AL80, I need to add 5 lbs of buoyancy to offset the weight of a full tank at the beginning of a dive. If I put enough air in my drysuit to offset that 5 lbs, I end up with a pretty big bubble that floats all over my drysuit depending on how level I am. Sometimes I end up floating sideways because the bubble is all on one side. Eventually, it ends up at my feet and I have to get vertical to redistribute the bubble.

Using my BCD to offset that 5 lbs of air is much easier for me. During the dive I have to vent the BCD as air is consumed. I only inflate the drysuit to offset squeeze and vent on ascent.

I don't inflate the drysuit to maintain warmth. If I was cold during the dive, I know my undergarments were not thick enough. Adding air to get warmer only makes my back warmer (where the bubble is) everything else still stays cold.

 

[60plus]

When correctly weighted, you will be heavy at the start of the dive by the amount of air you haven't yet consumed.

I agree with this but what I find in both wet suit, drysuit and bcd is that it is very difficult to get rid of all air at start of dive, it works its way out during the dive. This in dive loss of air compensates for increased cylinder buoyancy as its air is used.
As anybody who has followed my posts knows I am mainly a warm water wetsuit (or just swimming trunks) diver but I have a drysuit for colder dives in UK. My drysuit instructors were two very experienced technical divers so I assume their emphasis on maintaining constant drysuit displacement to maintain neutral buoyancy is well founded.

 

[Seaweed Doc]

I teach PADI Dry Suit periodically. I don't have the manual with me, but my recollection is that the language is more along the lines of "divers in shell suits often use the suit for buoyancy" while those in neoprene suits use the BCD.

Perhaps not true universally, but also not a commandment from PADI. I use the bcd for buoyancy and suit air for squeeze/warmth in my neoprene suit.

The following is even more suspect than my recollection of the manual's verbiage:

Decades ago (1990s?) I recall hearing that some power (maybe NAUI, maybe AAUS) mandated that dry suit divers use the suit for buoyancy. The concern was that using the bcd could trap your hand against the dry suit inflator button and cause runaway inflation of the suit. Sounds crazier now then back in the day. Think Mae West inflation on early BCDs, even the ones with backpacks. And mostly, if not all, drysuit inflator on the chest, push button to inflate. Even so, I thought it was highly unlikely.

 

[Jhgt2d]

Yeah, PADI teaches this method. It works "kinda well", right until you're diving doubles and have a valve failure that you have to send your left arm up to deal with the failure behind your head. At that point, you have a valve failure AND your buoyancy has just gone to absolute hell as you vent the buoyancy out of your rig when your arm goes up to close that valve. So you have a valve failure, down one reg, and you're descending uncontrolled until you can find a way to re-establish buoyancy again.

@jlcnuke I was taught that when doing a left post shutdown you use your right hand to fully close your drysuit exhaust valve and push the exhaust valve to the left, out of the way of your left forearm so it doesn't get trapped or in the way of your left arm reaching back to close the left valve. Never seemed to slow anything down so I don't think it adds any time to the shutdown.

 

[inquis]

it is very difficult to get rid of all air at start of dive

No doubt that's true. Thinking about it further, a neoprene drysuit probably gains some buoyancy over that at the stop depth. I can see that being a major contributor to a "slow" initial descent in such suits.

 

[Ulfhedinn]

Drysuit is for exposure and bcd for depth and compression control.

i put just enough air in my suit to relieve the squeeze, I use my wing for what it is intended for.

THIS!

 

[lexvil]

THIS!

Or not!!