Question on drysuit and buoyancy

[TSandM]

I had a very interesting conversation with one of my diving friends yesterday. He had been really upset with the dump valve on his dry suit -- he was convinced it wasn't working properly. He felt that it just wasn't dumping when it ought, and I remembered feeling that way, myself. I told him he wasn't putting enough air in the suit, and he didn't at first believe me. But yesterday, I apologized for having forgotten to give him the dump valve I promised him he could try, to see if it would make a difference, and he told me it was no longer an issue. I asked how he solved it, and he told me . . . he started putting more gas in the suit

I think the bottom line is that air in the dry suit is not something to be afraid of. It is something to MANAGE. When you are beginning, it can be difficult to manage a larger and more mobile bubble, so you keep it smaller. As you gain facility with the suit and with diving in general, you can expand that bubble, because you can manage it. To a point, a fuller suit is a warmer suit, so there's a payoff for learning to manage more air there. The suit cannot be used to manage buoyancy past a certain degree, so if you are diving big doubles, you simply have to put gas in the wing -- at least, you will if you use the weighting strategy of "neutral at 10 feet with 500 psi in the tanks". Many people diving doubles aren't properly weighted by that metric -- they are frequently not carrying enough weight to do it, which makes it less difficult to manage buoyancy with full tanks, but could be a problem in the event of anything that caused major delay or significant gas loss.

 

[eelnoraa]

For the gloves, I would recommend Si-Tech Glove Lock QCP (but its size can make it cumbersome). I can take mine off faster than any wet or dry gloves out there on the market.

This maybe hijack, but I think Ben would like to know the answer too. Can Si-Tech Glove Lock QCP fit work with DUI zip seal suit?

 

[Jerry_]

Hi, I am diving with drysuits for 15 years and use #1 (BCD on surface, drysuit under water for buyancy); but I agree that everybody should find his own best practice.

So you might ask why I am going for #1.

Point 1: BCD on surface
If you use the drysuit on surface, while having the head out of the water, all the air that would be in the drysuit would be in the upper part of the drysuit (your throat), and that is not comfortable ... defintely.

Point 2: Drysuit for buoyancy:
One point to add here: I use a wet suit in summer and the drysuit when temperatures in the water drop below 5-6 Celsius. When it comes to these temperatures I am using the drysuit for not getting cold, unfortunately a drysuit that has not a minimum of air isn't a good thermic insulation (so there has to be air in it anyway) and this air is subject to the (usual) compression of gases (i.e. The deeper you dive the more the air in the drysuit is compressed; i.e. The less it isolates from the cold).

My first drysuit was a trilam, my current is a compressed neopren. Even so the effect was more important with my first drysuit it is still valid for the neopren one, too.

So, having air both in the BCD and the drysuit means managing two volumes of air. In case of a problem, this can result in a lot of stress to empty both the BCD which you would use for buoyancy and the drysuit for thermic comfort. The same applies if your buddy tries to help you.

Another problem that you will face is (again) the compression of gases when you are doing your divestops. (don't forget that the relative compression rate for changing 5 meters varies with the depth at which you are).



In general I would say:
- new divers should always start with wetsuits and a BCD/wing for experiencing buoyancy
- always take a training before starting to use drysuits and find out what is best for you
- if you are using a drysuit in relatively warm water (lets say 18C) you may keep the habits of using the BCD for buoyancy
- if you are diving with a drysuit in cold water, close to 0 Celsius, you might prefer to use only the drysuit for buoyancy
- the choice you make can be influenced by the type of equipment that you have
- always do it the same way
- if you use the drysuit for buoyancy open the dump valve half way

 

[TSandM]

In general I would say:
- new divers should always start with wetsuits and a BCD/wing for experiencing buoyancy
- always take a training before starting to use drysuits and find out what is best for you
- if you are using a drysuit in relatively warm water (lets say 18C) you may keep the habits of using the BCD for buoyancy
- if you are diving with a drysuit in cold water, close to 0 Celsius, you might prefer to use only the drysuit for buoyancy
- the choice you make can be influenced by the type of equipment that you have
- always do it the same way
- if you use the drysuit for buoyancy open the dump valve half way

I agree with most of this, but would like to take a small issue with a couple of points.

I certified in a dry suit. I would not have done it wet, not unless we had gone somewhere VERY warm. I would not say that doing your OW in a dry suit is EASY, but it is survivable, and for those of us who are thin and cold, it can make the difference between doing the dives and not being able to tolerate them.

I also dive my dump valve all the way open, all the time, except when I have a valve which is getting on in years, in which case it may need to be clicked down a couple of points to avoid having it leak. If your trim is good, there is no reason not to leave the valve totally open, and I think it can be a safety thing.

 

[Storker]

In general I would say:
- new divers should always start with wetsuits and a BCD/wing for experiencing buoyancy
- always take a training before starting to use drysuits and find out what is best for you
- if you are using a drysuit in relatively warm water (lets say 18C) you may keep the habits of using the BCD for buoyancy
- if you are diving with a drysuit in cold water, close to 0 Celsius, you might prefer to use only the drysuit for buoyancy

I'm definitely not experienced enough to have any opinion, but I'd like to add a datapoint:

Where I live (middle Norway), the dive centers offer only dry suits for their OW courses. So just like TSandM, I certified in a dry suit. Like everybody else in my class. And in a snug-fitting neoprene dry suit, air movement really isn't much of an issue for me.

A wet diver is something we don't see very often, almost everybody dives dry here, even during summer. It's not so much the water temp; when you get down to 15-20m, it's never warmer than 10-11 degrees C whether you're up north or further south in the country where wet suits are quite common. The big difference is topside. With a wet suit you come up pretty chilled, it's maximum 15 degrees and probably raining, and you just can't get warm. With a dry suit you come up comfortably warm, and you keep warm between dives without needing a warm house to take shelter in.

 

[Tigerman]

Not to mention when you take it off between dives, its a LOT easier and more comfotable to put on for the second one than wetsuits are...
The only wetsuit I own is a Scubapro profile 2,5 shorty and lets just say its never been used anywhere but the red sea..

 

[bpotkin]

I have only 14 dives with my drysuit. I can dump air quicker from my BCD than my drysuit.
On a couple of dives, It took me 12 feet or so of ascending to get back under control, due to
trying to dump air from my drysuit. Regarding air getting trapped at my feet, I feel using
my DS for squeeze only, makes more sense. PS: I love my drysuit!

 

[NAM001]

i have not been in a situation that the ds is used for other than squeeze control and backup for wing failure.

 

[Storker]

I have only 14 dives with my drysuit. I can dump air quicker from my BCD than my drysuit.
On a couple of dives, It took me 12 feet or so of ascending to get back under control, due to
trying to dump air from my drysuit. Regarding air getting trapped at my feet, I feel using
my DS for squeeze only, makes more sense.

Of the limited amount of dives I've had, all of them - except the pool dives during OW class - dry, I've never had a problem with uncontrolled ascent. As previously mentioned, air trapped at my feet is not an issue either. If I feel that my feet are getting a tad light, I bend my kness and press my calves against my thighs to squeeze air out of my legs. I have no problem standing on my head allowing all the air to pool in my feet before flipping to horizontal, and I like to do that once in a wwhile just to keep my skills fresh.

At my level of skill and experience, using only the DS for buoyancy control under water significantly reduces task loading. That way I only have one bubble of air to remember to vent if I'm getting too light. If it's at all relevant, I dive with a single 15L/200bar tank and jacket-type BCD, and I don't carry more lead than absolutely necessary. I'm actually considering adding a kilo or so to allow for some more air inside the suit at depth for insulation and comfort, because I certainly don't feel I have a big bubble of air down there.

To those who claim that you need a lot of air in the DS, I don't understand the logic. If I'm correctly weighted at the surface with very little air in the DS, I'm definitely not going to look like a blob of air at depth. Boyle takes good care of that: whatever air I've got in my DS at depth is nicely compressed to keep my total volume the same as at the surface.

My only problem so far with using the DS for buoyancy control is that I have to train myself to use the BCD before vacationing abroad to dive wet.

 

[Bopper]

I've just started diving dry as well. I try to use my BC for buoyancy as much as possible as I hate the shifting air feeling of the suit, but when it gets really cold I let air out of my BC and put air in my suit. Instant warmth. However, prior to an ascent I like to let air out of the suit and put air in my BC. Probably not the best policy when it comes to maximizing air use.