Wet Suit Compression : Overweighting

[The Kraken]

I've a problem I've been trying to sort out for years and I'd like some help from the members of the august board.

At this point, a dry suit is not an optional means of solving the problem, so I'd appreciate it if that is not offered as a resolution.

To wit:

When I dive cold waters or in the winter, I'm doubling up my 6.5mm. The farmer john and jacket provide excellent warmth and comfort. I'm comfortable in this unit and, at this point, haven't had to take classes in other regimens, i.e. dry suit diving.

The problem arises when I hit that 15' mark when the wet suit compresses and loses a substantial portion of its bouyancy. In cold, fresh water I require 22 lbs. of weight to submerge, and that being with some difficulty in the absence of a down line.

Once at depth the reverse proble arises. The weight required for me to submerge now makes me overweighted. Trimming with increased bladder inflation and controlled breathing certainly makes things better, but is there something that I could do that I'm missing?

 

[nwdiver2]

You should be slightly negative at the surface with your BC empty. In cold seawater and two layers of 7mm neoprene the problem as you describe is worse. We teach the students to deal with it and use proper BC technique when the suit compresses and to watch out on the ascent starting at the 30 foot mark as the suit expands. They have to be neutral should a deep dive require a 15 ft safety stop. Quit using the down line for support, you are not over weighted, in sea water I have seen 28-30lb needed for a student to be comfortable on descents and be able to hold at 15ft for a safety stop on ascents. Some Large students 6’4” 280-290 are covering in a lot of neoprene I never teach students to descend head first and swim the suit down to get through the first 20-25 feet, they would then not have the correct bouncy at 15ft for a safety stop should they need it.

 

[The Kraken]

At the surface, at the beginning of the dive with my BC empty, I exhibit the customary bouyant condition, water half way up the mask. At this point I'm carrying 22 lbs. of weight.

Exhaling in the customary manner, and bringing all of my limbs in closer to my body to increase my apparent density I still have difficulty getting down the first 15 feet before WS compression occurs.
I'm not "using the down line for support". When available, in the diving scenario outlined, I use the down line to facilitate my descent.

Because of the loss of bouyancy due to WS compression the weight required to get me down causes me to be more negatively bouyant at depth requiring that I use my BC more than I would like to maintain a neutral bouyant condition. I especially hate this in extremely silty conditions, which are generally the majority of my dives.

 

[RPanick]

Unfortunately, there really isn't much you can do about it. You go deep, your wet suit compresses, you loose buoyancy. End of story. All you can do is put air in your BC and compensate.

The same thing happens to dry suit divers, the difference is that they can control the compression in the suit, that's why they don't need to put much air in their BCs. Its just a question of where you put the air.

Bob

 

[Boogie711]

Not quite the same thing happens with drysuit divers, Bob. If you're diving a neoprene drysuit, yes, your suit compresses. But if you're diving a shell suit, there's no compression, period. Any air that was still trapped in your suit on the surface would compress, but then again, you shouldn't be using your suit for bouyancy.

 

[fdog]

Yep. I also experience a whopping bouyancy change in the top 45' also, when diving wet with multiple thick layers.

Just something I plan for, thankfully not that often.

All the best, James

 

[Scuba_Vixen]

"At the surface, at the beginning of the dive with my BC empty, I exhibit the customary bouyant condition, water half way up the mask. At this point I'm carrying 22 lbs. of weight."

You should be like this *at the end of the dive with an empty tank* .... You should sink easily at the beginning.

Unless you are diving a steel tank that's negative when empty, 22# sounds low for that much neoprene.

If you figure you'll loose ~20# of bouyancy at 80' or so with the suit you describe, that should be about 50% of your bc capacity or less (<50% wing inflation ) ..As your gasload depletes, you'll become less negative, so you'll need less wing inflation as the dive progresses.

Once you get enough experience with it, it's not all that hard to manage. Obviously, it's most difficult the shallower you are ... midwater safety stops are the nut crackers.

Darlene

 

[The Kraken]

"You should sink easliy at the beginning" equates to even more weight resulting to an even more overweighted situation at the bottom if my basic high school physics course serves me right.

 

[DeepTrip]

Ye Kracken, you're right, but if I recall my training, you should float at eye level when your tank is empty (500 psi/20 bar), not with full tank. Then you will need to add 2kg to compensate for the gas you use during the dive.

Well, if you insist on loosing weight, bring 1kg (2 pounds) of your weight in separate belt. At your safety stop, try releasing the 2 pounds, and put it on the sand, while holding the end of the belt. If you can still float easily with empty BC, then you can ditch the 2 pounds. Otherwise, you're not overweighted. I tried that in my last dive, and I use 2 pounds less in my next dive.

 

[Kim]

My last instructor mentioned 'crushed neoprene' as the material for the wetsuit of choice. I've never actually found it - but the idea sounded good. As it's 'pre-crushed' it doesn't lose so much of it's bouyancy supposedly - or rather, it never had it to start with!! Does anyone know about it?