Drysuit Size Clarification

[Panama Jones]

OK. So this may seem like a dumb question and I might be able to think it through but I have cold water brain freeze at the moment and when I hear you answers I’ll probably go ..Duh! to myself.

I have just decided to go dry and have about 12 no issue dives in my drysuit. Found it quite easy and very warm. The question I have is all the comments about how important it is to have a properly fitted drysuit to avoid a large roving air bubble which could present a dangerous situation.

My point, even the perfect fitting drysuit will allow a bubble many many times too large for proper buoyancy control. If you put too much air in, you will have a large roving bubble, period. It doesn’t appear to me that it has anything to do with how much air the suit will hold, but how much air you need to add to maintain neutral if you use the suit for buoyancy or to take the squeeze off if you use your BCD for buoyancy (let’s not turn this into a debate about this). Once you are at depth and before you add your first shot of air, as much air as possible has been squeezed from your suit and it's hugging you tight. You only add enough air to meet your warmth or buoyancy needs. Doesn’t matter if you’re in a 5 gallon bag or 8 gallon bag.

My Trilam is a little big and off the shelf, but doesn’t matter because once it's hugging me I only add enough air to get loft for warmth. I may agree that there could be a problem if it is so large that a bubble gets trapped in a fold but for the most part, once you get your first squeeze at depth, air will take the path of least resistance.
So I always here the advice that if you are not a perfect off the rack body type, you require a customized suit as a suit too big (within reason of course) is a danger. I challenge this advice as well as the comment below.
This from dive website. “A snug fitting suit and undersuit will tend to have less air in it and therefore less to move around while a baggier suit may have more in it to give the extra insulation”

Someone tune me in.

 

[PfcAJ]

A properly fitting suit is best. Like you said, there's chance of weird stuff happening due to the bubble. Folks with legs shorter than their drysuit legs have even had their fins pop off when inverted! Plus, all the extra material just slows you down.

 

[Redshift]

Not only with the excess material air can get trapped or move to less desirable places and be harder to guide to where you want it, but also, since there is more suit, I suspect you need more air to alleviate the squeeze because some air will get into suit folds while the rest of the suit will still be pressing against your body until you add extra air.

 

[Subcooled]

If you have a thick undersuit then air will migrate slowly. Try diving with a base layer only and you will truly learn what an air bubble is. And it is always in the wrong place: left foot, right foot, both feet, left arm, right arm, around your throat (least favorite), on the move...

Only people that dive in warm water want to minimize gas in the suit. The gas, air or argon, is the thing that isolates you (as long as it's static). But it also makes you big and not very hydrodynamic so swimming fast or against current becomes hard work. More air also expands more rapidly on ascent and requires care and planned dumping. These two issues can be big risks. If you dive in current in warm water, then you want a wetsuit or a slim drysuit. If you dive in stagnant +2C water, then you want air, wool, and heating inside. You then must practice accordingly as ascents become more challenging.

Some people like cold less than I do. They often use the Weezle extreme plus and hence, they need 2-4lb of extra lead, and they also tend to tape the left arm under the exhaust vent. They believe it makes dumping air easier. They all dive well.

You should ask yourself these questions:
1) do I have just enough lead to stay warm during deco, and no more?
2) does my undersuit fill by drysuit?
3) can I ascend 10 inches and stop, at 10ft? Great. Now repeat that 10 times.

 

[TSandM]

I agree with you -- if there is very little air in the suit, it has a harder time causing problems. But if the suit balloons, air can get trapped in the excess fabric and make it much more difficult to move it up to the valve to vent it. This is typically a problem in the legs or sometimes in the back. The range of what can be considered "acceptable" fit is large, though; for example, the Fusion suit relies on a very oversized inner bag compressed only by a Lycra outer skin, and that works fine.

 

[Glenn08]

I like my Viking dry suit vs. neoprene. The suit material has no buoyancy. A neoprene suit would change buoyancy with depth. I think the 'roving bubble' problem would be caused by wearing more lead than necessary. When properly weighted, just enough air to compensate for squeeze should also be neutral buoyancy.

 

[Subcooled]

I have dived in a pool with drysuit and base layer only. If I do this using steel 12/232 tanks there will be an annoying bubble and an undersuit would help. If I dive with one neutral stage tank hand held, and nothing else, diving is easier. So yes. The amount of air is important.

 

[decompression]

Remember, a drysuit is a horrible BCD, it is there for warmth. Only enough air for warmth and that should eliminate squeeze. If you maintain proper trim and attitude the air movement shouldn't be an issue. Even when moving significantly the small amount of air in the suit will be negligible.


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