dry suit and buoyancy

[eod]

I use both. When diving single tank setup I usually use the suit for bouyancy. This is easier because the amount of air to prevent squeeze is almost enough to make me neutral, so I put a little extra in and become neutral. This is in a thick undergarment that traps alot of air and prevents air from moving around. If I used a thinner undergarment I might use the wing here instead. You don't want a moving bubble of air in the suit.

When diving doubles I use the wing. I tried to use only the suit once, I got a really big bubble of air moving around, very hard to control.

 

[mempilot]

Bouyancy Compensator - compensates for bouyancy.

Dry suit - keeps you dry.

Any questions?

Gotta go with Boogie on this one. Put just enough air in the suit to reduce the squeeze to a comfortable level. If you eliminate the squeeze totally, you've got too much air in the suit. If you are putting a lot of air in the suit to stay warm, you need to change your undergarments to a warmer undergarment. You hear all kinds of whacked ideas on this subject.

BC - bouyancy
drysuit - stay dry
undergarments - stay warm

If you live by this, you can put yourself in pretty much any position underwater in your drysuit and not have to do the tuck and roll.

BTW, if you wear heavy doubles, you'll want your center of bouyancy mated with your center of gravity. Using the BC will allow this, where as using the suit for bouyancy will cause an unbalanced condition. You can end up head down and feet up in no time.

 

[ScubaSarus]

If it is that cut and dry, why is it all the literature I've read including intruction manuals from the drysuit makers tell you to use the drysuit for bouyancy. Is this just because it may be a safer practice or are they just following the PADI standard as to limit liability. I don't know and would like to get the origin for this practice.

Chris

 

[Ber Rabbit]

I too use the bc for buoyancy and the suit for staying dry. I've had a lot of problems with the suit while learning to use it and I found that using the bc for buoyancy gives me the option of easily dumping excess air before starting to ascend. This allows me to focus on getting in the proper position to dump the drysuit (the vent sits in a funny place on my upper arm because I'm so small) and control my ascent speed. I have buoyant fins (which I hate) and even with ankle weights my fins float above my head making my life generally difficult in the drysuit.

Do a proper weight check with a 500 psi tank, I found out that I require about 8 pounds more lead in the drysuit than in my old 1/4 inch wetsuit to be neutral at 15 feet with an aluminum tank that's low on air.

Now I just have to figure out how to stay warm in the thing, I freeze in 60 degree water while wearing 400g thinsulate undies.

Good luck and enjoy!
Ber :lilbunny:

 

[mempilot]

I'll expand a little. Since the drysuit receives and exhausts gas, it is a bouyancy control device. You must learn how to use it as one, just as you mastered the bc vest in training. However, when studying the center of bouyancy as it relates to the body, you'll see that the majority of our mass and weight when geared up is at the torso. That is why the bc is worn in this region and not at the legs or arms or other parts of the body. We are compensating for the negatively bouyant properties of the extra weight we wear while diving. By spreading the air allong the entire body, we would create an unstable situation requiring the need to manipulate the air back to the center of gravity. This would return us to a stable situation. You can minimize this by keeping the air in the suit to an absolute minimum.

Training agencies don't allways teach best practice. DIR has pioneered some widely accepted best practices that PADI and other haven't adopted yet. The long hose, the bp and wing, standard gas mixes, etc... Manufacturer's are the same. If a manufacturer doesn't tell you to learn to use the drysuit as a bcd, then they run the risk of being sued when you can't control the bouyancy of the suit and are injured. The suit becomes a secondary bcd to the wing, jacket, etc...

If it is that cut and dry, why is it all the literature I've read including intruction manuals from the drysuit makers tell you to use the drysuit for bouyancy. Is this just because it may be a safer practice or are they just following the PADI standard as to limit liability. I don't know and would like to get the origin for this practice.

Chris

 

[Boogie711]

The reason PADI wants you to use your drysuit for bouyancy instead of your BC is because they think divers are too stupid to be able to handle the 'increased taskloading' of handling BOTH a drysuit inflator and (gasp! horror of horrors!) a BC inflator.

Seriously. They don't want students being 'taskloaded.'

This is especially sad because it's PADI which has put the majority of those 'taskloaded' people in the water to start with.

 

[mempilot]

LOL. I get taskloaded wading through all of their certs, while reading all their marketing brochures, while opening all the junk mail they send me, while keeping their DM candidates from touching my tank valves, while...

The reason PADI wants you to use your drysuit for bouyancy instead of your BC is because they think divers are too stupid to be able to handle the 'increased taskloading' of handling BOTH a drysuit inflator and (gasp! horror of horrors!) a BC inflator.


Seriously. They don't want students being 'taskloaded.'

This is especially sad because it's PADI which has put the majority of those 'taskloaded' people in the water to start with.

 

[Snowbear]

Gotta go with Boogie on this one. Put just enough air in the suit to reduce the squeeze to a comfortable level. If you eliminate the squeeze totally, you've got too much air in the suit. If you are putting a lot of air in the suit to stay warm, you need to change your undergarments to a warmer undergarment. You hear all kinds of whacked ideas on this subject.

BC - bouyancy
drysuit - stay dry
undergarments - stay warm

If you live by this, you can put yourself in pretty much any position underwater in your drysuit and not have to do the tuck and roll.

BTW, if you wear heavy doubles, you'll want your center of bouyancy mated with your center of gravity. Using the BC will allow this, where as using the suit for bouyancy will cause an unbalanced condition. You can end up head down and feet up in no time.

I was taught it was the undergarment that keeps you warm, but only if it is lofted with air. I've found that any more air than needed to loft the undies (just a bit more than needed to relieve the squeeze) is too much and I start getting that bubble migration causing dynamic instability. Not enough and not only do I get cold faster, my mobility (especially arms) is hampered. It's pretty cool when folks ask me later how I can be "head down vertical like that" to look under something and when I'm done I don't have to struggle to return to horizontal. Same deal when I'm supine in the water column with my doubles and a flip of the fins and I'm prone again - that's a bit harder when I have the weight of the tanks behind and the gas bubble in front :11:

 

[mempilot]

I was taught it was the undergarment that keeps you warm, but only if it is lofted with air.

Just like snow ski attire. Only problem is, when the water temp is cold, the air mass between the undies and the shell will eventually cool if the shell is thinner than the undies. ie. trilam vs. neoprene. If submersed in warmer waters, the air we feed the suit is warm and this isn't much of a problem. If submersed in cooler water, the air from the cooled tanks is fairly cold in its self. Kind of like air conditioning your suit and reducing the heat your body created. There will always be air in the suit unless you hook up a vac before you dive. All we need to do is keep that comfortable pre-dive volume constant by adding a little as we go down. Fleece under the suit will help spread the squeeze and keep pinch points from happening. As little as possible is the key. You defineatly need some, just not the amount I've seen some divers trying to manage. - think Michelin Man LOL

 

[DA Aquamaster]

I too use the bc for buoyancy and the suit for staying dry...

....Do a proper weight check with a 500 psi tank, I found out that I require about 8 pounds more lead in the drysuit than in my old 1/4 inch wetsuit to be neutral at 15 feet with an aluminum tank that's low on air.

Now I just have to figure out how to stay warm in the thing, I freeze in 60 degree water while wearing 400g thinsulate undies.

Some advocates of the "dry suit only to stay dry" approach also advocate only keeping enough air to keep most of the squeeze off and state that if you are comfortable in the suit, you have too much air in the suit. Ie:

Gotta go with Boogie on this one. Put just enough air in the suit to reduce the squeeze to a comfortable level. If you eliminate the squeeze totally, you've got too much air in the suit. If you are putting a lot of air in the suit to stay warm, you need to change your undergarments to a warmer undergarment. You hear all kinds of whacked ideas on this subject.

This inevitably leads to being cold in the suit as well as squeezed as you are not allowing enough air in the suiot for it to properly loft the insulation. The situation ends up being exactly the same as with a wet suit where depth compresses the neoprene and reduces its ability to insulate. A little more air in the suit will often do wonders for warmth. If you are feeling squeezed you need more air and if this small amount of additional air causes stability problems, you need a better fitting suit.

From a practical standpoint if you are diving single tank with a reasonably sized tank (80 cu ft or less) and are properly weighted, and have a properly fitting suit, you should be able to use the drysuit for bouyancy and not lose any stability.

If however your suit is poorly fitted or if for any reason you are carrying extra weight (stage bottles, double tanks, etc), then use of the BC for bouyancy control becomes neccesary.

Given the tendendcy for tech divers to have doubles, stage bottles, cannister lights etc along for the ride, it is no surprise that nearly all are advocates of the "dry suit only to stay dry" approach. Where it gets a little narrow minded and sanctimonious however is that this view then gets extended by some to advocating that using the BC is the only correct way to do it with various conspiracy theories following as to why training ag3encies still adhere to the other way of doing it.

Persoanlly, I don't see nay need to stand on one side of the fence or the other. It makes more sense to just get rid of the fence and use what ever approach works best on an particular dive with a particular configuration. If for whatever reason on a dive, a diver has to put too much air in the suit to maintain neutral bouyancy, then obviously all they have to do is vent some air from the suit and add some air to the BC. But this is not to say a single tank rec diver with a good fitting suit is ever going to need to add air to the BC.

Just do what the situation demands and don't get hung up on having to adhere to one particular point of view or the other.

And if you want to get the most out of a drysuit, don't spend your whole diving career sqeezed in the thing as you will be missing the primary benefits of drysuit diving -warmth and comfort.