DAN advocating using drysuit for buoyancy control while diving

[Storker]

I add air to the suit at the beginning of the dive to loft my undergarment and get warm. If needed, I add air to the wing after that for buoyancy

I do it the other way around. When descending, I add air to my wing to arrest descent and achieve neutral buoyancy. After that, the air I add to my suit to alleviate squeeze and keep my undergarments properly lofted is enough to offset buoyancy swings due to depth. As the dive progresses and my air supply depletes, I gradually vent my wing to keep squeeze away. At the end of the dive my wing is pretty much empty and I'm somewhat shrink-wrapped at my safety stop. It's always a relief to add air to my suit after surfacing.

If I only add air to my suit to stop my descent, I have issues with floaty feet and poor trim control due to air travel until I approach the end of my dive.

 

[Dhboner]

Thew majority of my dives are shore dives Storker so arresting the descent is not an issue but when boat diving I definitely use your protocol.

 

[Storker]

Thew majority of my dives are shore dives

Mine, too.

arresting the descent is not an issue

I guess it depends on how much water you have beneath you when you vent your wing to submerge. I like to paddle out until I have at least some 5-8m between me and the bottom before I give the thumbs down to my buddy and we go down. Then I stop my descent at about 5m by filling air into my wing, and then I start filling my suit.

 

[Jim Lapenta]

The new SDI drysuit materials have a section titled "Your drysuit is not your BC". I know because I wrote it that way. This was after one of the training dept members had a discussion with a number of manufacturers. The drysuit is not designed to be a buoyancy control device. It's exposure protection.

With proper weighting it is possible to have it so that adding air to offset squeeze also accomplishes allowing one to be neutral. However it is dangerous for an over weighted diver to rely on the suit for control. This is the problem with new divers venturing into drysuit use with this idea. A drysuit typically does not vent as fast or efficiently as a BC. Inverted it may not vent at all unless the boots pop off. A BC can be vented in most any position thanks to the rear dump valves. It is easier to manage a larger volume of air in the BC.

New divers and new drysuit divers are not overly task loaded managing the suit and the BC if properly weighted and trained. To insinuate that they are is insulting to them. If there is a problem you fix it with better training and a more competent instructor. Not bad info that with today's better undergarments and more streamlined suits that don't require as much air in them could pose a danger to them. The Barsky manual was good for it's time. It's now outdated and not up on current practices. Or current suits and undergarments.

 

[Storker]

Inverted it may not vent at all unless the boots pop off.

If my boots pop off, I just lose my fins. No venting involved. To vent through my feet, I would have to stab my boots with my BFK. Which probably would leave me thoroughly flooded, wet and miserable. Plus with the need to patch my DS.

 

[FishLovingStudent]

If you are cold water diving, why would you not use your drysuit for buoyancy? It keeps you warmer, gives you uniform lift across your body, and venting gas by doing a chicken wing tilt dump in trim is easier than lifting the BCD hose.

You get into a feet first ascent? Do a U-Swim and dump...you learn this in the course. As for beginners not being task loaded if they are managing two air spaces, I disagree. Almost any openwater would be task loaded by it, basic buoyancy skills are hard enough with one air space let alone two. I know when I was in OW, managing one buoyancy control device underwater and two just on the surface was already overwhelming enough. Watching over classes, we need to constantly remind students to dump. The only reason I am considering switching to the suit for squeeze and BCD for buoyancy is I'm in sidemount and want to see if the SM BCD's lift is better for trim (though it appears unnecessary so far with only two tanks).

Understandably in configurations where you are heavy and require a lot of air in your suit to get neutral you need a BCD for buoyancy but it's unlikely any recreational diver is going to run into that. In what situation is a recreational diver going to be using a large volume of air underwater to achieve neutral buoyancy? And if you are upgrading to doubles or multi-tank setups you should have no problem switching your buoyancy technique. I could use my BCD...just not my preference, ideology, nor what I was taught.

 

[Storker]

If you are cold water diving, why would you not use your drysuit for buoyancy?

I guess I'm a cold water diver (3C to 12-15C water). In practice, I use both the wing and the suit. Like Jim Lapenta said, if you're properly weighted, the air needed to offset squeeze pretty much equals the air needed to control buoyancy. OTOH, there's the buoyancy swing from full to empty tank to consider. In my winter undergarments, there's too much air in my suit at the beginning of the dive to avoid excessive air travel and trim issues if I only use my suit. In the summer, with thinner undergarments, that's less of an issue.

Understandably in configurations where you are heavy and require a lot of air in your suit to get neutral you need a BCD for buoyancy but it's unlikely any recreational diver is going to run into that. In what situation is a recreational diver going to be using a large volume of air underwater to achieve neutral buoyancy?

What size tank are you familiar with? Al80? That tank holds less air than the normal European size rec tank (steel 15Lx200bar, or steel 10Lx300bar). My tank's buoyancy swing is some 3-3.5kg from full to empty. To avoid shrink-wrapping at the end of my dive, I weigh myself so that if I use my suit only for buoyancy, I have a rather big bubble to manage during the first phase of the dive, and it becomes awkward to avoid trim issues and floaty feet. Using the wing for long-term buoyancy control, filling it somewhat at the beginning of the dive and slowly venting it as my air supply depletes keeps my suit air bubble at a manageable size. Short-term buoyancy swings due to changes in depth are easily managed by just using suit air, as the air needed to offset squeeze basically takes care of my buoyancy issues.

 

[FishLovingStudent]

AL 80s (SM & BM), Faber 50s (SM & BM), Steel 80s (SM & BM), 100s (BM), and 120s (BM).

In my experiences so far, I have had no problem with using only my suit for buoyancy. As it is the most common technique taught around here, even taught by the more tech orientated shops (albeit not for tech diving), I don't see any reason to change. I have not experienced a situation (nor any recreational diver/instructor I have talked to) where I have so much air in my suit that it is uncomfortable, but I agree that if that did occur I would switch to a BCD/Drysuit method.

The recreational tanks here are AL80s and even with two AL80s, drysuit only buoyancy has sufficed so far. If I were to jump to 3 or 4, or double steels? We'll see :blinking:

 

[boulderjohn]

I dive with an HP120 and see almost a 9 lb swing from full to 'on-the-boat' That is a lot of air in a suit, no thank you.

If you read my full post and not just the last sentence, you will see that I said that what you do depends chiefly on the weight of your system.

A single tank diver with an AL 80 will have maybe a 5 pound swing from the beginning of a dive to the end. If you typically have a 9 pound swing, you are at the near equivalent of diving a set of AL 80 doubles. So, it would make sense that your buoyancy needs would be more similar to a technical diver than a recreational diver. It would therefore make sense that you could not achieve buoyancy from your suit alone.

 

[Storker]

why don't you add or dump air as needed throughout the dive to both maintain buoyancy and to avoid squeeze?

I do. Short-term buoyancy control: suit. Long-term (over the time of the dive) buoyancy control: wing. If I don't add some air to my wing in the beginning of the dive, I keep comfy and warm, since my undergarments are thoroughly lofted, but I get somewhat floaty feet and suffer from lack of trim control due to excessive air travel.

I guess it all boils down to small differences in weighing, suit snugness, acceptance of air travel inside the suit and trim issues. No diver is equal, and (IMO) every diver has to find what works for them and their gear setup.