Question Help with wing lift

[inquis]

I'm intrigued now as to whether flooding the drysuit, and thus saturating the undergarment with water, may cause a (partial) loss of buoyancy that the undergarment provides, and how meaningful that might be?

The undergarments provide support for the suit, and there's a lot of air between the fibers. That volume provides lift that must be countered by mass (e.g., lead) to be neutral. If you totally flood the suit, that lift is gone (I've tested it) -- and yet you still have all that lead, so you'll be very negative without compensating somehow. So yes, it could be "meaningful".

Fortunately, the odds are that you'll still have a functioning wing that can serve that need. If not, then a buddy, DSMB, or dropping some lead will likely be required to get you off the bottom. It's quite difficult to swim up when more negative than about 15 lbs, and muscles don't work well in very cold water.

 

[crofrog]

I'm intrigued now as to whether flooding the drysuit, and thus saturating the undergarment with water, may cause a (partial) loss of buoyancy that the undergarment provides, and how meaningful that might be?

I can be significant. If you fully flood. Most floods are partial and you can keep some air in the suit

30 for singles and 40 for doubles are the "standard" GUE recommendations for Fundamentals students, at least sampling the instructors I have interacted with.

Generally speaking wings are sized based on the diameter of the tank.

40lb doubles wing for 7" tanks
60lb doubles wing for 8" tanks
20 to 30lb single wings for 7" tanks
40lb single wing for 8" tanks or when you've got a lot of weight and accessories.

In building a balanced rig, the hardest part for me has been to understand the undergarment buoyancy, as I've seen rather larger ranges mentioned, including by GUE instructors (e.g., 5 to 15 kg of lift).

In my swimsuit I'm basically neutral I freshwater.
In my shell drysuit with just rash guards I need ~2-3 lbs, with my 200weight undergarments I need 8, with my FE halo 3ds and a heated vest and dry gloves I need ~28lb.

 

[inquis]

In building a balanced rig, the hardest part for me has been to understand the undergarment buoyancy, as I've seen rather larger ranges mentioned, including by GUE instructors (e.g., 5 to 15 kg of lift).

Best thing to do is hop in the pool and just measure your buoyancy while wearing each combination of layers you would use: breath from a tank on the bottom, add suit gas, and vent from the shoulder exhaust while in trim. Drop weight until you can't stay down at the end of a normal exhale.

Yes, it varies quite a bit. Mine ranges from +4 kg (wicking layers alone) to +13 kg (4th Element Arctic + Xerotherm layers together), but I've not been in water colder than 4°C.

 

[landphil]

I'm intrigued now as to whether flooding the drysuit, and thus saturating the undergarment with water, may cause a (partial) loss of buoyancy that the undergarment provides, and how meaningful that might be?

That calculation I did was for enough lift to float the rig with a full tank and all of the lead- which is a super nice feature if you're diving from a boat where you don & doff your BC in the water (I've even done one beach dive where the conditions were extreme enough that it was pretty dangerous to walk in or out fully kitted- but that's gotta be a wetsuit dive, and the team effort of getting everyones BCDs out over slick rocks and through big shore break gets super abusive on your gear)

You definitely are going to lose a lot of positive buoyancy if you replace all of the air in your drysuit with water. However, any water you add would not add to your negative buoyancy. Your wing lift still only needs to offset the weight of your tank/backplate/lead to float you (still ignoring that your body & lungs are going to make you even more positive buoyant- but there's no requirement to fill your wing all the way for your ascent.) The extra water you've loaded into your suit just comes along on the ascent for free

 

[crofrog]

Best thing to do is hop in the pool and just measure your buoyancy while wearing each combination of layers you would use: breath from a tank on the bottom, add suit gas, and vent from the shoulder exhaust while in trim. Drop weight until you can't stay down at the end of a normal exhale.

I do it almost the exact same way, with the difference being that I break trim fairly significantly and really try to get as much of the gas out as I can without resorting to crazy arm pumping and the likes.

My thought process is the only time I'll ever end up that light is with basically empty doubles, at even 500psi you've still got ~2lb of gas in a set of double 80s so I'm ok measuring with a lot more squeeze so that I know I can stay down if I need to but for normal finishing pressures I'm a bit lighter.