dry suit buoyancy

[Mako Mark]

I just checked the PADI specialty outline and nowhere is there an objective that requires the use of only the DS for bouyancy, however, this appears in the reccommended training sequence for dive 2.

Descent.
a. Standard descent; neutralize buoyancy during descent
— use dry suit only. Watch for suit squeeze.

I also found this in the academic presentation:

1. BCDs for use with dry suits — although under most
circumstances you maintain buoyancy underwater with
your suit (more about this later), you always use a BCD
when dry suit diving.
a. The BCD provides emergency buoyancy if you get a
substantial leak in your suit.
b. The BCD provides a more comfortable way to float at
the surface.

and this

4. Adjusting your buoyancy underwater.
a. Underwater, you add air or argon only to the suit. Do
not use your BCD.
1. This avoids a suit squeeze (severe pinching due to
compression as you descend).
2. You’re not having to control two systems —
adding or releasing gas as you change depth.

I can only speculate, but it seems that PADI think it is too complicated to manage the BCD and the DS inflation and deflation at the same time.

Given what I have just discovered, I would possibly try the descent on dive 2 using only DS inflation, in order to demonstrate that it can be done that way and allow the students to see the difference and decide.

Personally I just use the BCD for bouyancy control uw as the response time is quicker.

 

[Sideband]

The drysuit dump valves weren't designed to be used for buoyancy control. They dump air far to slowly to stop a runaway ascent and you get left with pulling open the neck seal and flooding the suit as one of the only ways to stop it. The BC was designed to vent air faster. It isn't uncommon for very soft undergarments to block the suit dump valve.
Drysuits were designed to keep you dry. A BC was designed to control buoyancy.

I'd also like to see where PADI requires this for AOW. That would be a pretty hard requirement to fulfill in tropical water diving a 2mil shorty.

 

[scubascobey]

Thanks for all the great replies. I do think that if I can master buoyancy (hovering for 5 minutes) with just my DS, that my skills will improve. But I think for safety and control, I'll ultimately end up putting just enough air in my DS to relieve sqeeze and for warmth, but the rest I'll manage with my BC. If I keep my DS valve set right, the air comes up easily when ascending, and the BC I can manage manually, which I'm comfortable doing. This DS only buoyancy has me spooked with popping up...handling the air purge when needed. I guess I need to only put enough air in my DS to fin pivot, then clear my fins, then work on lung control to do the rest. If I'm properly weighted, I shouldn't have the roll issue with the heavy steel tank.

Wish me luck for my dive this Wednesday!!!

 

[Rick Inman]

Well, the people I see who use their DS for buoyancy seem to do the following:

* Feet are floaty, so they add ankle weights.

* Trim now out due to ankle weights, so add tank weight near valve.

* Descend feet first and plunge into bottom.

* Dive negative (heavy) and keep swimming so as to not plunge into the bottom.

From what I've seen, if you do these things, your instructor should happily pass you through the class.

 

[Tigerman]

Well, the people I see who use their DS for buoyancy seem to do the following:

* Feet are floaty, so they add ankle weights.

* Trim now out due to ankle weights, so add tank weight near valve.

* Descend feet first and plunge into bottom.

* Dive negative (heavy) and keep swimming so as to not plunge into the bottom.

From what I've seen, if you do these things, your instructor should happily pass you through the class.

I do none of the above?
Then again, I dont have the DS specialty card

Its amazing what a simple thing like minding how high you hold your feet can do..

 

[DeepDog]

It refreshing to see from this thread that I’m not the only dry suit diver who understands the safety (and control) advantage of having an auxiliary device dedicated to the control of buoyancy thus allowing for minute increments of adjustment while also allowing for the immediate purging of air in the (extremely unlikely) event of an unexpected assent.

What a novel concept, a device for controlling buoyancy at varying depths and pressures; perhaps we could call it a buoyancy compensating device or BCD. It could even be used to supplement the buoyancy contribution of the air in a dry suit required to relieve pressure squeeze and provide thermal qualities.

But seriously folks, my ankle weights came off long ago and I haven’t missed them and if my BCD only had a single purge valve located in a position that only functioned when my feet where dragging then I might consider risking my dry suit for buoyancy but I’d more likely trash the BCD for a real one.

I know ScubaScobey will make it through this class showing the skills necessary and go on to become a seasoned northwest diver.

 

[PinkPADIgal]

It can be very difficult to control your buoyancy using your DS, as you have observed. Most--if not all--of the drysuit divers I know use their BC to control buoyancy.

If I may ask, where did you get the idea of using your DS for buoyancy control?

It sounds like I am in the minority in this group, but I control buoyancy almost exclusively with my dry suit. I have done it both ways and I think it depends on the diver, the suit and undergarments the diver is wearing, and how much weight they have. I have found, for me, I am more comfortable, use less weight and stay warmer when all the air goes in my suit.

 

[gcbryan]

It sounds like I am in the minority in this group, but I control buoyancy almost exclusively with my dry suit. I have done it both ways and I think it depends on the diver, the suit and undergarments the diver is wearing, and how much weight they have. I have found, for me, I am more comfortable, use less weight and stay warmer when all the air goes in my suit.

I agree in that if you know how to dive you can do it regardless of equipment. I use my BC for buoyancy but if correctly weighted once you have enough air in your suit for warmth and to offset squeeze it's not necessary to use all that much in a BC in the first place.

However, I don't think anyone really needs to use ankle weights. If the boots are attached and are a little too big fin keepers are a much better solution.

 

[Dive Bear]

Ok, all kidding aside, here are the facts.
</Rant mode on>
You should dive with just enough weight on your belt to be neutral when your suit is empty. If you can hit the dump valve on your BC and sink like a stone, you are overweighted.

Divers who are overweighted tend to plunge to the bottom like a stone or pop to the surface like an overfilled balloon. The reason for this is simple. If you are overweighted, you must put more gas in SOMETHING, be it your BC or DS or both. When that over large volume of gas responds to the effects of pressure due to a change in depth, the resulting change in buoyancy will be violent when compared to a diver who has learned to dive without overweighting.

Say anything you want, but most divers are overweighted. I can tell by the way their heads drop out of sight when the hit the dump valve on their BC.

If you have a problem with runaway ascents when using your DS for buoyancy control, you have a defective valve on your DS or (more likely) you are seriously overweighted.

If you have a problem with a large volume of air moving around your suit, which will result in all manner of trim and stability problems, you are seriously overweighted.

By definition, if you have enough gas in your suit to make it feel like you are wearing a balloon, and you are still negatively buoyant, you are seriously overweighted. In this case, any amount of high volume dump valves in your BC or your suit will not make you comfortable or safe.

I know I'm beating this to death but I will say it one more time. When I put enough gas in my suit to relieve squeeze, I don't need any extra gas in my BC, because I'm already just about neutral. I stay just about three to four feet off the bottom and I prefer to swim in a slight head down feet up attitude as I find this works well in high silt environments like Puget Sound. Leg weights? I don't need no stinking leg weights and I can hover just fine, ask anyone I dive with.


Don't take my word for it, please check out this link:

http://www.mindspring.com/~divegeek/bcwtbelt.htm

Dr. Taylor has forgotten more about dive safety than most of us will ever know and his web site should be required reading for all studnets and instructors.

</Rant mode off>

 

[TSandM]

Thanks for the link -- That's a great site to bookmark and share with others.