Question on drysuit and buoyancy

[Akimbo]

I am not sure I fully understand. It is difficult not to use both while biasing toward the most convenient.

It also depends on the suit and underwear. My first dives with a commercial drysuit were in a 6mm Neoprene Poseidon Unisuit in the 1970s (aside from deep sea gear). The exhaust valve was manual and the horse-collar Fenzy was for emergencies only (dedicated bottle, no hose to your tank). No option there. The suit was the BC and was much more like diving a deep sea rig than a modern drysuit.

The other extreme is a custom/great fitting compressed Neoprene or laminated suit with tight fitting coveralls (like a White’s Fusion) and automatic exhaust valve. Controlling suit squeeze pretty much sets buoyancy regardless of depth unless you want to fool with your exhaust backpressure — an ergonomically less attractive option.

A trilam that fits like a garbage bag is much different, and IMHO requires far more attention. An uncompressed Neoprene suit almost demands using your BC, especially with doubles or the bubble interferes with attitude control (lots of change due to suit compression and weight of exhausted gas).

I find the simplest in a modern non-compressible suit is to adjust the exhaust valve for minimal backpressure and add just enough to avoid discomfort. Beyond that, treat buoyancy control like diving a wetsuit.

 

[boulderjohn]

In recent threads we learned that the dry suit class materials for just about every agency say to use the dry suit for buoyancy. The book Dry Suit Diving, written by the DUI leadership, says the same thing. It goes on to explain the same thing that TSandM said--it is easier to focus on one buoyancy device as a beginner, but in time you will learn to do both.

Those who say you can't control heavy tanks with the little bit of buoyancy in a dry suit are missing the fact that it is assumed you have put enough air in the BCD to get in the ballpark of buoyancy and then are using the dry suit for the fine tuning changes that occur during the dive.

On the other hand, in my experience most people say they prefer leaving the dry suit just filled enough for comfort.

As for me, I use both, and it depends upon the circumstances. It depends a lot upon where I am in the dive, especially if I have large tanks and am looking at a 16-20 pound swing in weight. Sometimes its just easier to give myself a little jab in the chest for added buoyancy, or lift my arm to have less. In the videos I watched while in my UTD classes, all the UTD instructors were using their dry suits to manage the buoyancy changes upon ascent.

 

[rhwestfall]

it seems that #1 is taught for the reasons discussed, and many adopt #2 as it appeals to them afterwards. Each has benefits and drawbacks. Find your Zen.....


for me, its #2....

 

[ajduplessis]

My zen supports #2

 

[pasley]

To each their own. For both camps the BCD is used on the surface. Below the surface no one solution is right for all situations. For me, recreational diver, single tank above 110 feet (and normally above 80) the amount of air required to keep the suit infliated for squeeze and warmth is enough for buoyancy as well. This gives me one bubble to manage. If I find that to not be enough (has not happened in several hundred dives) I would then add air to the BCD. Yes the bubble can and will move around a lot more than the bubble in a BCD, but like anything else, you learn to manage it. You have to manage it no mater what you do. For others diving doubles or going deep they very likely have other considerations. Variables such as equipment, undergarment, depth will all influence the decision as to what method works best.

So as others have said and as some of the manuals have said, there are two camps on this, Chevrolet and Ford. Which is better is dependent on what you like and what you use it for.

 

[USFpsychDiver]

Put me in the #2 camp. In the extreme, if using DS for buoyancy, if you need to dump a bunch of air you've got squeeze and if you have to add a bunch of air you've got Michelin man. The BC, being a smaller, more confined airspace, is easier to control than the DS 'bubble'. Controlling trim with a DS full of air can be an issue; not so with a properly designed and adjusted wing. The DS does provide redundant buoyancy; as my cave instructor said, if you're diving wet and have a wing failure it's a long walk out.

 

[TSandM]

Now, try that with a drysuit. Are you still in trim? Not likely.

Well, if I either fill my BC or my dry suit with gas, I'll be on the surface, and likely not in any kind of trim at all . . . but I CAN put enough gas in my dry suit to have it burble out the dump valve, in horizontal trim, and still be in horizontal trim.

Guys, there is no right answer and wrong answer here. The right answer is to do what works for you; you need to be in trim, and you need to be neutral, and you need to be able to manage an ascent. It's my personal observation that using a dry suit for buoyancy, for a brand new diver, is a nightmare; they're not stable enough in their posture to keep the air where it should be, and they don't anticipate buoyancy changes well enough to be able to stay ahead of the curve on venting. The "20 foot squeeze" is not a bad approach for a new diver!

But once you are comfortable enough in the water to be able to maintain a horizontal position, and have enough bandwidth to anticipate that you'll need to manage your buoyancy when you're ascending, you can put the gas where you want it. In cold open water, I keep as much in the suit as I possibly can; in a cave, I'll squeeze that suit right down, because I know I'm going to have to adopt "unusual attitudes" as the cave imposes them.

You do what works, and what works may change as your ability to manage your equipment changes. The same person from whose teaching I learned the 20 foot squeeze is the one who took the dump valve off my wing during a training dive.

 

[mahjong]

Can't recall if I made an issue of this here on SB, but I have asked many people about it in person: If you rely on your wing/BC for buoyancy control at depth then when you lift your arm to vent the wing/BC you will also, simultaneously, vent your drysuit, unless you have closed off your drysuit exhaust valve. I am not advocating using the drysuit only for buoyancy control. But I would like to know how people prevent the drysuit from dumping when you lift your arm to dump your wing/BC. If, like DIR/GUE recommends, you rely chiefly on your wing for buoyancy control, then you will be very often during any dive raising your arm, with LP inflator in hand, to dump air from your wing when you need to. If your drysuit exhaust valve is open, then you will almost always ALSO be dumping air from your drysuit.

How do people, esp DIR/GUE people, cope with this? Do you shut down the drysuit exhaust valve, partially or completely? If so, what are the implications of this, esp during the ascent?

 

[Tigerman]

Just adjust the ds exhaust pressure to where it "should be" for your comfortable ammount of air in the suit?

 

[mahjong]

Not at all sure what you mean by this? That so-called comfort level changes during the course of a dive with your depth. If I go from 100' to 60', a whole lot of air in my DS will have expanded and needed to have been dumped to have the same comfort level with minimal air in the DS. Same is true of the air in my wing, though proper trim/neutral buoyancy rather than comfort is the goal. It is not an easy task SIMULTANEOUSLY to dump the correct needed amount of air from a wing and DS on the same lift of an arm--and after which to be comfortable with warmth/squeeze in the DS and in proper trim/neutral buoyancy with BOTH the wing and DS.

I have been trying it out and I get the same feeling each time I do it as I have when I play roulette in Vegas or Macau.

Just adjust the ds exhaust pressure to where it "should be" for your comfortable ammount of air in the suit?