Drysuit use and buoyancy

[grf88]

With my first dry suit, a Bare Nexgen, I used the BC for primary buoyancy but when I switched to a Whites Fusion I started to use the dry suit as the primary means of controlling buoyancy and find that I just need to shrug my shoulder to vent. The Fusion does dive differently from the Nexgen.

 

[mafi]

Yes, easier to control and I see no point in packing along extra lead just so I can add air to the wing.

Nobody suggest you should add weight just so you can have air in your wing. That would mean overweighting yourself.

Sounds to me like you have several litres of air in the suit in the beginning of the dive that should/could be in the wing, though.

 

[boulderjohn]

Nobody suggest you should add weight just so you can have air in your wing. That would mean overweighting yourself.

Sounds to me like you have several litres of air in the suit in the beginning of the dive that should/could be in the wing, though.

I don't think he is saying that anyone is suggesting they overweight themselves just so that they can have air in the BCD. He and I are both suggesting that many people who are advocating having air in the suit and using air in the wing for buoyancy control are overweighted, probably without realizing it.

If adding just enough air to the drysuit makes you neutrally buoyant, then why do you also need air in the wing?

 

[lexvil]

Nobody suggest you should add weight just so you can have air in your wing. That would mean overweighting yourself.

Sounds to me like you have several litres of air in the suit in the beginning of the dive that should/could be in the wing, though.

Or not

 

[mafi]

OK then, I misunderstood. Thanks for the clarification on what you meant!

 

[Jim Lapenta]

Absolutely. If you are overweighted, you will need to add air to the BCD as well.

As a technical diver, I am vastly overweighted (by the recreational definition) on almost all my drysuit dives, so I am used to using my wing as my primary buoyancy controller. It is different for single tank recreational divers.

It does depend on what size single tank. With an al80 I can get away with enough to take the squeeze off being just about right for buoyancy. With my Lp95s or the LP119's or 120s I may borrow from the shop for deeper dives (100-130ft) in Lake Erie with a stage under my arm? The wing has to come into play.
Even on shallow stuff with heavier steel singles I don't need as much air in the suit to take the squeeze off so the BC is used for primary buoyancy and that's how I teach it.
One of the other considerations is the undergarments used. Some of the new materials don't require as much loft for warmth as the older materials did. The SDI materials note this as well as the recommendations from manufacturers who clearly say that the suit is for exposure protection, not primary buoyancy. This was made clear by the mfgrs when we were revising the course and I wrote it that way.
It wasn't always about what it took to take the squeeze off.
It was necessary to have enough air in the suit for the undergarments to make use of to stay warm. I noticed this right away with the difference between my 17 yr old OS Systems garments and the 4th Element ones I use now. In addition to being less bulky, they don't require as much air to be effective.
My "heavy" OS systems is bulkier than my mid range 4th Element but takes more air to prevent being compressed so that it actually keeps me as warm. As a result the amount of air to offset queeze and provide effective insulation is greater with the older one.
Not a big deal for me with going on close to 700 drysuit dives. But when I've taught drysuit classes I've seen people go for the BC for buoyancy first. Sometimes it's clearly out of muscle memory. Without practice and good training, using the suit is, to them, counter to what they learned up until that point. I've also noted that people managing two sources of control (three really if you count lung volume and should do that) is not that big of a deal with a course that isn't rushed and where they have good control coming in.
It's all about bubble management. Putting the lungs aside, managing a smaller bubble in the suit is easier than dealing with a large one. So using both the suit and BC makes more sense in some ways to me and it's been much easier for those I've taught.

 

[Wibble]

With my Lp95s or the LP119's or 120s I may borrow from the shop for deeper dives (100-130ft) in Lake Erie with a stage under my arm? The wing has to come into play.

(For info, what pressure are LP 95s & 120s normally blown to? Want to convert that to litres)

 

[HKGuns]

I manage my buoyancy with my dry suit. I don't see much point in managing two separate air pockets.

 

[Jim Lapenta]

(For info, what pressure are LP 95s & 120s normally blown to? Want to convert that to litres)

It depends on whose doing the filling. I have "heard" of them being filled to 3300-3500 PSI so that the 95 holds 118-125 cu ft and the 119's are closer to 148-158 cu ft of gas.

 

[Jim Lapenta]

I manage my buoyancy with my dry suit. I don't see much point in managing two separate air pockets.

It helps to keep the volume of air down in the suit. This could be a critical issue if the diver gets inverted or the suit dump has a problem. Certain types of undergarments have been known to get sucked into the valve and cause it to not work as well or at all.
Or if the diver is using doubles or diving sidemount with steels, it makes managing the bubble harder because it's larger. I've personally seen divers add too much air to the suit and not be able to dump it quick enough and, as a result, pop up to the surface, get inverted and end up on the surface hanging upside down, have gas escape out of the neck seal allowing 40 degree water in, and struggle with trim because the suit doesn't fit like it should in some areas and the gas gets into those.
You already manage two areas with a wet suit. BC and lungs. Adding a drysuit, with proper training, is not a big deal. Managing two spaces is often easier than managing one big one.