Question on drysuit and buoyancy

[Tigerman]

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.

The dump valve on a DS can be twisted to adjust the pressure before it automatically release air to be anything from michelin-man to shrinkwrap.
If you set it to "slightly uncomfortable" it will release air automatically when you ascend to keep you "slightly uncomfortable" - you shouldnt need to touch it..

 

[eelnoraa]

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?

I don't exactly know how I mange, but here is what comes to my head. I am mostly horizontal and use butt dump to dump the wing even in ascent. So raising left arm to dump wing air isn't very common. If I go vertical for whatever reason, since the dump value is on upper arm, there still have air above the valve that won't vent out. And don't forget, air in right arm is also trap unless I lower the right arm. So there is quite a bit of air in the suit, more than enough to prevent the squeeze when I return to horizonal.

Also, wing inflator dump much quicker than the suit valve. So by the time enough air vent from the wing, the suit will just vent very small amount of air.

 

[PfcAJ]

If you're ascending and need to dump from your BC, its probably safe to say that you'll need to dump from your suit, too.

Sometimes (but not all the time), I'll use my corrugated hose to dump and go a little head up, which dumps my suit, too. This is especially handy when going up and down hills while on the scooter.

 

[mahjong]

Well, dumping from the rear is quick and easy when wetsuit diving a single tank with a small donut wing in the tropics. Reach back, give the butt a tiny bump up, and give the rear dump a quick tug and it's done. When doing this kind of diving I always rear dump and it's nice. But it's a bit trickier when drysuit diving with dry gloves and double tanks and a larger wing (esp a horseshoe wing) and an argon bottle. I am diving a horseshoe wing right now (Halcyon 40# Explorer). A tug on the rear dump cord usually results in the entire wing flap moving forward without any air being dumped. A snugger fitting donut wing (like the Evolve) might remedy this--more air moves to the OPV because of the donut and donut wings tend to be cut trimmer, reducing the problem of the flap moving forward without air dumping. I typically don't have trouble finding or pulling the dump cord, even with dry gloves, but it's not quite as quick and easy as grabbing the LP inflator and raising it for a quick burp while lifting my shoulder a bit--but here is where the drysuit will also burp, unless I have closed down at least some my DS exhaust valve.

Rear dumping might be one of the "tricks" if you're using mainly your BC for buoyancy control. I wonder if there are not others as well?

I don't exactly know how I mange, but here is what comes to my head. I am mostly horizontal and use butt dump to dump the wing even in ascent. So raising left arm to dump wing air isn't very common. If I go vertical for whatever reason, since the dump value is on upper arm, there still have air above the valve that won't vent out. And don't forget, air in right arm is also trap unless I lower the right arm. So there is quite a bit of air in the suit, more than enough to prevent the squeeze when I return to horizonal.

Also, wing inflator dump much quicker than the suit valve. So by the time enough air vent from the wing, the suit will just vent very small amount of air.

 

[rhwestfall]

When diving my DS (and this is true cold water), I tend to ascend in a somewhat verticle position, tolerating a little squeeze on my legs. With that, I have the confidence of my shoulder valve being easy to activate, and also my dump valve on my wing being at the hightest point too. Just what I do.... YMMV.

 

[FinnMom]

Those think the answer is and should always be #1 or is and should always be #2 can get really, really vehement about it. Don't let them bother you. That's the message I wanted to post.

Otherwise I'd say TSandM said it first: both are used, beginners more typically #1 and then more and more towards #2 as the ability to multitask increases.

 

[Them]

I can understand the vehemence.

I have a dry suit book from SSI (picked it up at a used book store while researching suits).

I have the manual (pamphlet) for SI Tech dry suit valves, titled "user's guide to optimized buoyancy control"

I have an owner's manual for a dry suit.

"WARNING: DO NOT attempt to use both the dry suit and BC for controlling buoyancy." (This is in a box with a warning symbol)

"Unexpected buoyancy and rapid ascent can be caused by any equipment attached to you that can change in volume due to content of gas (i.e. BC or certain suit materials). This is why [we] recommend the BC to normally be emptied of gas during the dive."

Of course the SSI book also says #1 is the only safe method.

When the official word is so consistent, most people will follow that authority. People will only move counter to the textbook if they have strong opinions of their own. That's a recipe for vehement disagreement.

Is there any sort of objective test that could be applied to both methods? Something to make it less subjective?

 

[TSandM]

You can't test it, because it's dependent on diver skill. I have no problem today managing two air spaces; I had tons of trouble doing it when I was a new diver. If you ignore either air space on ascent, you are likely to have trouble. You MUST put air in the suit to retain mobility, so the suit can't be empty. You don't HAVE to put air in the BC. That's why they teach to leave the BC empty . . . but then you're putting all the air in a very large bag, where body attitude has a big effect on how easy the gas is to dump. Having done more than one feet-first ascent early in my career, I can testify that if the gas gets into your feet and legs, it's not easy to recover, no matter which of the maneuvers you were taught in your dry suit course you elect to try.

I found that, if I was using my wing primarily for buoyancy, I didn't have so much gas in the suit that the amount that would escape when I lifted my inflator hose was a problem. As AJ says, if you need to vent, you need to vent; if there's enough gas in the suit that it escapes quickly when you lift your arm, you probably needed to vent the suit, too. My biggest problem when using the wing for buoyancy was that I'd try to vent the suit when there wasn't really enough air in it to get much out, and I'd leave the wing too late. I have learned to get all the gas out of the wing first (if there is any there, as there is when I am diving doubles or 130s) and vent the suit once it's gotten nice and loose and easy to get air out of.

 

[eelnoraa]

.... But it's a bit trickier when drysuit diving with dry gloves and double tanks and a larger wing (esp a horseshoe wing) and an argon bottle. I am diving a horseshoe wing right now (Halcyon 40# Explorer). A tug on the rear dump cord usually results in the entire wing flap moving forward without any air being dumped.

I see what the problem is. The trick here is NOT to pull the dump cord forward. Since the wing will somewhat wrap around the tank. If you are horizontal, you pull the cord up, away from your back, and even a bit toward the tank. Think of it as if you left hand is reach around behind your back. Hard to describe, but if you dive with Andrew again, watch him.

 

[mahjong]

I see what you're saying, Aaron. When wetsuit diving and rear dumping I literally go head down and feet up, so when I pull the cord it is an upward and not downward pull. But in a drysuit and carrying double 100s I don't go head forward to the same extent. Next time out (should be Thursday) I will attempt doing an exaggerated upward pull on the OPV cord instead of downward/forward. I will also keep an eye on Andrew.

Also like TS&M's point about taking care of the air in the BC/wing first. Towards the latter part of a dive when the big tanks are getting low--after 75-90 minutes--there should be no more need for air in the wing. At this latter stage the wing can be empty and air managed chiefly in the suit, so single tasking. And it is at this latter stage when you're holding stops for deco or to shoot a bag or whatever.

I see what the problem is. The trick here is NOT to pull the dump cord forward. Since the wing will somewhat wrap around the tank. If you are horizontal, you pull the cord up, away from your back, and even a bit toward the tank. Think of it as if you left hand is reach around behind your back. Hard to describe, but if you dive with Andrew again, watch him.