A Tale of Two Cities (Drysuit-BC)

[hydro12]

"It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness"...etc etc.

In reading the material for PADI's Drysuit course (let's try not to go off on a tangent about agencies) they recommend using your BC strictly for inflation at the surface and using your drysuit for buoyancy below. This is recommended so you're only adjusting one buoyancy device instead of two, and I must admit, this line of reasoning makes sense.
However, while I'm sure there are different methods taught, I've read a majority of drysuit divers say they use both or only the BC below the surface, only adjusting drysuit to prevent squeeze at depth.

For those of you who dive dry and may have tried different permutations, which approach do you take and why did that one method work better for you than the others?

...."for good or for evil, in the superlative degree of comparison only."

 

[Thalassamania]

• There are only two non-emergency reasons to ever have to increase your buoyancy:
  • to compensate for squeeze as you descend, or
  • to compensate for the weight of gas at the start of a dive.
• If you’re diving a single tank of 80 cubic feet or less, then the 5.8 lbs (or less) of shift from the start of the dive to the end (were you to drain your tank) can easily be accommodated within your drysuit without upending you and blowing off your flippers. But that’s about the limit, any more gas than that an you should use a BC or BP/W for buoyancy.
• If you’re diving a single tank of more than 80 cubic feet, or doubles, then you'll need to add air to a BC or BP/W at the start of the dive, to compensate for gas you will be using, and keep it adjusted during the dive as you change depth and burn gas. That can get interesting so it's good to have two baselines:
  • Know what your suit “feels” like when it’s volume is adjusted to neutral.
  • Calibrate your breathing so that you know the volume of a full exhalation and so that you’ve trained yourself to exhale a smaller volume with some consistency (e.g., I can hit two real easily, every time).

I rather suspect that PADI was limiting its scope and vision to a single 80 or less, and thus made a reasonable statement.

 

[nucem]

When I started using a drysuit I would use both the suit and the bc to control buoyancy. My buoyancy sucked. Once I got better at using the drysuit and properly weighted I found I only needed to use the suit. I would suggest using the suit a much as possible and try all the methods and see which works best for you.

 

[hydro12]

Thank you for the responses. I imagine further practice will help develop what works for me.

Thal, you're most likely correct - I'm sure PADI religates its context to light recreational diving. Makes sense now that you say it.

 

[xiSkiGuy]

Having tried both, I prefer using my bp/w for buoyancy control and adding air to the suit only for squeeze. Some advice I gleaned from ScubaBoard was to try and maintain a 20ft squeeze in your drysuit. This works well for me. YMMV.

 

[Jasonmh]

I take the approach of just putting enough air in the suit to offset some squeeze, anything beyond that I use the BC for. I tried using the suit only, but didn't like it at all. I have a much easier time making finer bouyancy adjustments with the BC than I did with the drysuit. Venting from the DS when I had too much air in it usually had me venting too much, then having to add some back.

 

[cummings66]

I've used both methods and practice both, just in case. I prefer using BC as a BC and using the drysuit to stay dry and I'll add enough air to it to offset squeeze.

 

[in_cavediver]

First, I was taught the PADI way and after diving doubles, did it the other way. Here's the best advice out there:

1) Adjust the suit so you are comfortable, warm and not squeezed. This is the MAX air you will want in your suit. This also corresponds to about what your need for the balanced rig with a 63 or 80.

2) If after 1, you still aren't neutral, use your BC. In general, this is due to a larger quantity of air you are carrying. (otherwise, you could drop the wieght). In doubles, you could be carrying 20lbs of air and that's a lot for a drysuit to handle alone. (Michelin man anyone?)

It is far more comfortable to keep the required amount of air in your suit and no more. If you try to do it all with your suit, you'll expierence diving in a 'bubble' or shifting air in your suit. (really screws up your trim) How much air you need to be comfortable will depend on a lot of things. Water temp and cold tolerance being the big ones.

 

[Thalassamania]

First, I was taught the PADI way and after diving doubles, did it the other way. Here's the best advice out there:

1) Adjust the suit so you are comfortable, warm and not squeezed. This is the MAX air you will want in your suit. This also corresponds to about what your need for the balanced rig with a 63 or 80.

2) If after 1, you still aren't neutral, use your BC. In general, this is due to a larger quantity of air you are carrying. (otherwise, you could drop the wieght). In doubles, you could be carrying 20lbs of air and that's a lot for a drysuit to handle alone. (Michelin man anyone?)

It is far more comfortable to keep the required amount of air in your suit and no more. If you try to do it all with your suit, you'll expierence diving in a 'bubble' or shifting air in your suit. (really screws up your trim) How much air you need to be comfortable will depend on a lot of things. Water temp and cold tolerance being the big ones.

I do a slightly more rigorous and systematic analysis, but we come out rather close to the same thing. Good advice.

 

[hydro12]

Thanks for the advice.

cavediver and Thal, I know it doesn't directly translate, but just as a reference, for a single al80 and also for double steel Xs, how much weight do you wear w/ your drysuit?