First Drysuit Dives

[1_T_Submariner]

I did two dives yesterday afternoon for the first time in a drysuit. Pretty cool feeling to take it off and the undergarments are still dry!
Other than being over weighted on the first dive it was a great day of diving.

I do have one question. I have read a lot of posts on how to use a drysuit etc... There seem to be two ways to control buoyancy
1. Put just enough air in the drysuit to relieve squeeze and then use your BC.
2. Let all of the air out of your BC and use your drysuit to control buoyancy.

What are the advantages/disadvantages to each option?

 

[SeanQ]

This is a pretty common subject on ScubaBoard. I suggest reading this dynamic instability article for one reason why a drysuit isn't an ideal choice for a buoyancy controller.

 

[Pathfinder]

I think the article SeanQ linked to illustrates one very good reason to not use a drysuit for buoyancy. Another good reason is that pumping more air in the drysuit also increases the possibility of a rapid trip to the surface that you didn't intend for.

Dave

 

[SeanQ]

I think the article SeanQ linked to illustrates one very good reason to not use a drysuit for buoyancy. Another good reason is that pumping more air in the drysuit also increases the possibility of a rapid trip to the surface that you didn't intend for.

Dave

Not to mention a exhaust valve on a drysuit can't be dumped as quickly or in as many orientations as a BC.

 

[Spragg01]

SeanQ is right: do a search and you will find there are many threads on this topic.

Personally, I find that (when diving a single tank) when I am properly weighted, that I am neutral with my BC empty and my drysuit comfortably inflated. In this, I suppose I would be accused of using my suit as a BC. However, if you think back to buoyancy training (in terms of operating at depth) the BC is really only there to compensate for the loss of buoyancy in your wetsuit with depth, and to account for the extra weight you need to carry for your tank. With doubles or cases where the diver/gear density at the start and end of the dive are more disparate, the need and use of a BC while operating at depth is increased.

What I am trying to say, is that for your run-of-the-mill one tank rec dive, I strive to be weighted neutrally, and with a drysuit, that means with enough air in the suit to be warm AND neutral. If I need to use my BC, I’m over-weighted. My $.02

 

[Thalassamania]

Mr Chamberlin make complete sense, if you follow the minimuim sided BC link.

Whereas if you keep just enough gas in your drysuit to maintain the required loft of your undergarments and use your BC for buoyancy, then the gas can only travel the length of your BC which is a far smaller distance. And finally it means using the minimum sized BC wing for your configuration so that the gas in the wing has the least amount of distance to travel.

(edited thanks to Jon Sprague's pointing out the importance of the link.)

I don't find that uncontrolled "sloshing" air in my suit is much of a problem; in fact it can be used as a tool. Since I stay horizontal with my knees slightly bent and my fins high I have a small bubble across my shoulders and one at each calf. By shifting position I can move air from one location to another and use this "tripod" to maintain virtually any attitude in the water (be careful of feet or head straight up).

 

[Spragg01]

Reading further . . . if you follow the link "labled minimum sized BC wing" he states:

"The wing is used to control buoyancy throughout the dive; a drysuit (if worn) should only be inflated enough to keep warm (please see Dynamic Instability for more information). At the beginning of the dive add enough gas to the wing to offset the weight of breathing gas in your tank; as you breathe the tank down, gradually vent small amounts of gas from the wing to stay neutral. At the end of the dive, when you are at 10ft, if your tank is nearly empty there should be little or no gas left in the wing."

This seems to be is a better understanding of the ideal relationship between BC and drysuit (keeping in mind the need to add air to both as you go deeper). Personally, I'm not experienced enough yet to really feel a huge difference in buoyancy between a single AL 80 at 3000 and 1000, so don't bother with the wing except on the surface. If I got into doubles though, this would probably change.

 

[1_T_Submariner]

Thanks to all for your input! Great link to Dynamic instability.

 

[mikerault]

I find using a back-inflate BC with the drysuit and only using enough air in the suit for comfort to be the way to go.

Mike