Drysuit for buoyancy control??

[*Floater*]

I was at Dutch Springs yesterday, and bumped into 3 guys taking fundies. One was an instructor (for other agencies), all were experienced divers. We talked a little bit and they mentioned having to relearn various things. In particular, the guys said it was demanding to learn to use the drysuit primarily for buoyancy because they were used to just using the wing for that. To be clear, they said it was (and always has been) a combination of wing and drysuit for buoyancy control, but they were taught now to use the wing to offset the buoyancy swing from the tanks, and the drysuit for everything else, i.e. as the primary buoyancy control device.

I took my DIRF in a wetsuit, so I missed out on the GUE drysuit approach, but I kind of got the sense reading the internets that DIR-types preferred to use mainly the wing for buoyancy control, and the drysuit mainly to stay dry, as backup buoyancy, and usually just inflated enough to take the squeeze off.

So what's the deal?

 

[cool_hardware52]

I was at Dutch Springs yesterday, and bumped into 3 guys taking fundies. One was an instructor (for other agencies), all were experienced divers. We talked a little bit and they mentioned having to relearn various things. In particular, the guys said it was demanding to learn to use the drysuit primarily for buoyancy because they were used to just using the wing for that. To be clear, they said it was (and always has been) a combination of wing and drysuit for buoyancy control, but they were taught now to use the wing to offset the buoyancy swing from the tanks, and the drysuit for everything else, i.e. as the primary buoyancy control device.

I took my DIRF in a wetsuit, so I missed out on the GUE drysuit approach, but I kind of got the sense reading the internets that DIR-types preferred to use mainly the wing for buoyancy control, and the drysuit mainly to stay dry, as backup buoyancy, and usually just inflated enough to take the squeeze off.

So what's the deal?

Your question would be best put to the instructor of the fundies course in question, anything else will be speculation.

Having said that consider the "perfect" dry suit. By this I mean one where the internal gas volume always remains exactly the same, i.e. just enough gas to remove the "squeeze" If you descend you add gas, but don't change the volume and if you ascend you vent gas, but don't change the volume.

If the diver could achieve this "constant volume" dry suit then with the exception of the change in the weight of the gas the diver would remain neutral.

Of course the buoyancy of the diver's tanks will change during the dive, and that's what the wing is used for.

Nothing radical here, sounds like the instructor was teaching the standard approach to me.

Tobin

 

[*Floater*]

Tobin, what you said makes perfect sense, but what these guys were talking about just sounded different to me than the advice I've seen here. i.e. here on SB I've read suggestions along the lines of 'just inflate the drysuit enough to take the squeeze off and use the BC for everything else,' which is what I do, whereas these guys were saying that it's DIRer (and better) to use the drysuit beyond just taking the squeeze off, and in practice, to use it more actively than the BC. They were also talking about how great it (using more gas in drysuit than they had previously been using) was for their trim and overall form.

 

[cool_hardware52]

Tobin, what you said makes perfect sense, but what these guys were talking about just sounded different to me than the advice I've seen here. i.e. here on SB I've read suggestions along the lines of 'just inflate the drysuit enough to take the squeeze off and use the BC for everything else,' which is what I do, whereas these guys were saying that it's DIRer (and better) to use the drysuit beyond just taking the squeeze off, and in practice, to use it more actively than the BC. They were also talking about how great it (using more gas in drysuit than they had previously been using) was for their trim and overall form.

but they were taught now to use the wing to offset the buoyancy swing from the tanks, and the drysuit for everything else, i.e. as the primary buoyancy control device.

Once you compensate for the buoyancy swing of your gas with your wing what else is left?

Tobin

 

[nadwidny]

Tobin, what you said makes perfect sense, but what these guys were talking about just sounded different to me than the advice I've seen here. i.e. here on SB I've read suggestions along the lines of 'just inflate the drysuit enough to take the squeeze off and use the BC for everything else,' which is what I do, whereas these guys were saying that it's DIRer (and better) to use the drysuit beyond just taking the squeeze off, and in practice, to use it more actively than the BC. They were also talking about how great it (using more gas in drysuit than they had previously been using) was for their trim and overall form.

That's the first time I've ever heard of that coming out of a fundies class or any GUE class that I've taken. It has always been enough gas in the suit to relieve squeeze (how much that is has never been defined. I know that AG was all about shrink wrap.)and the wing for everything else.

 

[rjack321]

That's the first time I've ever heard of that coming out of a fundies class or any GUE class that I've taken. It has always been enough gas in the suit to relieve squeeze (how much that is has never been defined. I know that AG was all about shrink wrap.)and the wing for everything else.

GUE and AG both go back and forth contradicting themselves year to year. There is no "right answer." I have heard AG say to use only the wing and 2 yrs later to emphasize the suit. I have also heard active GUE instructors tell students that they are using the wing too much and the suit too much (different students).

If you are in trim and got your sheet together its all irrelevant. If you are freezing, ignore the pundits and put more gas in the suit (get better undies too). If you are constantly head down, maybe a bit more gas in the wing. Feet dragging, an extra puff in the DS and a tad less in the wing. Assuming the tanks are appropriate for you in the first place, there are a few tank/body combos that just don't work but generally speaking a skilled diver can manage most doubles by using the various suit/wing/plate combos available. Sometimes you can dive the ideal "constant volume" Tobin mentions, but in reality its rarely that smooth. Either the suit or the wing has "taken over" depending on where you are in the dive, how much gas you have remaining, how cold you are, how well the tanks 'align' with you body shape, etc.

 

[cool_hardware52]

Sometimes you can dive the ideal "constant volume" Tobin mentions, but in reality its rarely that smooth. Either the suit or the wing has "taken over" depending on where you are in the dive, how much gas you have remaining, how cold you are, how well the tanks 'align' with you body shape, etc.

I agree completely. I'm not suggesting that "constant volume" is either practical or achievable. I used the concept of constant volume to illustrate the idea that if the diver is properly weighted, i.e. negative by the weight of their back gas, the wing will start off displacing a volume necessary to offset the gas, and will be reduced though out the dive.

In practice, as you point out, other considerations such as warmth, freedom of movement and trim will change the division between wing and suit.

Tobin

 

[sheck33]

I used my drysuit for boyancy for the longest time. I switched to using my wing for boyancy and the suit semi shrink wrapped. I found diving that way far easier than managing the large airbubble in my suit.

 

[mer]

Depending on your undergarment, you may need more gas than "just enough to take the squeeze off." You need to make sure to have enough gas to fully loft your undergarment. Different undergarments (and similar undergarments of different degrees of wear) will take different amounts of gas.

The point is that more gas in the suit than what's needed to loft creates a bubble. We'd rather have this bubble in the wing as it confines the bubble to a smaller area and therefore creates less dynamic instability as we change positions while diving.

 

[BarryNL]

That's the first time I've ever heard of that coming out of a fundies class or any GUE class that I've taken. It has always been enough gas in the suit to relieve squeeze (how much that is has never been defined. I know that AG was all about shrink wrap.)and the wing for everything else.

Yeah, you only have to look at the standard DIR trim to see that putting extra air into the suit would be ridiculous. The lower legs and feet are the highest point and that is precisely where that air wants to be. Putting more air into the suit than needed to prevent squeeze is just going to make your dive miserable as you fight to prevent going feet up the whole time. Remember, ideal trim means that you can remain motionless in a horizontal position. That is only possible whilst you are balanced around your centre.