1969ivan1 wrote:I don't use a bc with my drysuit either. I am sure somebody (LUIS) will say that it is dangerous, but I see the the BC as UBER redundant when using a drysuit for some of the reasons already stated.
Wow!... there is a lot of hate here!
I never said that it was dangerous to dive a dry suit without a BC…but now that you mention it, in your case…it is probably dangerous.
Diving dry with no BC has been done many times.
Here are a few things to consider.
There is a huge difference between diving a full neoprene suit and a tri-laminate (or vulcanize rubbers, or even compressed neoprene suit). I own both a 7mm dry suit and a tri-lam suit and use them both.
The neoprene in the full neoprene suit will compress as much as a full wetsuit and will have a very large buoyancy swing. If you compensate for this buoyancy change with the suit you will end up with a very large air bubble in your back that will be shifting all over the place as you move. I have done it, and it can be done, but it very uncomfortable.
With any of the tri-lam (or any other non-compressible suit) it is fairly easy to only use the suit for buoyancy compensation (if the conditions are right, more on this later). To use the suit for buoyancy compensation it is much easier if you have good undergarments for insulation that maintain good loft and doesn’t compress easily.
In theory (and most of the time also in practice) the air you need to add to keep a tri-lam suit from squeezing you is also the same amount of air to keep you neutrally buoyant.
In reality you have to add about 5 pound of buoyancy extra to your dry suit to compensate for a full tank (assuming about a 72 cu ft tank). This is not very much and should be easy to manage.
Another big issue to consider is if you get cold and need to weight yourself for maximum insulation loft also. That can also make it more difficult to manage the air bubble as your body position shift.
With a tri-lam it can all be easily manageable if you have decent insulation and the water is relatively calm.
If you are diving in open ocean and there is a lot of surge, using the dry suit for buoyancy control can add another level of difficulty.
The vent in the drysuit is not very fast and in all situations it is very important to anticipate any need to dump air as you rise in the water column. Most dry suits have automatic dumps, but your body position needs to place the dump at the highest location to allow the air to vent. In a horizontal position you could have air trapped in your legs as the surge is moving you up.
A week ago I was doing a decompression dive during some relatively rough seas. The wave action and surge was high enough that my dive computer fast accent alarm was going off even when I wasn’t actually moving (according to the down line from my float and my other depth gauge).
On the other hand the surge was moving us enough that being horizontal with air in the dry sit was unmanageable. We ended up getting vertical to try to squeeze as much air as possible out of our legs and then using the BC for neutral buoyancy. Even then during the deco stops we all wanted to be a bit on the heavy side due to the surge.
That should be an unusual situation where I had to hold a decompression stop during a very high surge condition, but it is just something to keep in mind.
For most diving a BC is just a convenience…sometimes more than others, but it is very seldom an absolute need.
Oh about vintage dry suit, you need a Poseidon Unisuit (I actually have one of them that I have never used, I need to use it sometime). It is probably the only real vintage suit with a decent air compensation. It is a full neoprene suit, but it is so dense that the buoyancy may not change as much, but I don’t know.
