help with drysuit buoyancy calculation

[*Floater*]

perhaps if there's a major flood in the drysuit? let's say it happens at the beginning of the dive when i have all the gas weight. let's say i have 26lb of lead, variously distributed. i really dont know how much extra weight that flooded drysuit would add, but a 30# wing may not be enough to lift it.

of couse, i'd be swimming it up and have some of that 26lb as ditchable as a worst case scenario, so that may be a moot point.

i don't know if i'd need 40#, that's why i'm here. ; )

In your scenario, with a 26-30# wing, of which you would be using ~10# max to offset the gas in your tank, you'd still have 16-20# of spare lift left to compensate for the loss of dry suit buoyancy + you could probably generate another 5# with your lungs + you can also swim up a fair bit, maybe 10-20# ? And I imagine an instantaneous and complete drysuit flood would probably be pretty rare? Maybe if you jump in with an open drysuit by accident? In addition, you could carry a lift bag or SMB to generate another X# pounds of lift for emergencies (though deploying it in an emergency might be tricky - but you can always practice super fast emergency deployments). Also, you can also put some of your weight on the good old weightbelt or some place else where it's ditchable.

Personally I would not worry about the drysuit flood. I think 40# wings are needed very rarely for rec diving, and then only by large people using thick neoprene wet- or drysuits since they have to also compensate for the loss of buoyancy caused by the compression of the neoprene. And single tank, wetsuit-wearing tech divers may also need them.

30# is better as i'm trying to get the most streamlined possible. let's go the other way, then, would a 26# wing be enough?

If you are thinking about the DSS torus 26 (since that's the only 26'er I know) vs. LCD 30, then I'd personally go for the torus because it's a donut and I prefer donuts. But that's just my personal preference and a lot of other people don't seem to think it matters. However, there's a lot of people who bought the LCD 30 when the Torus 26 was not yet available, so I'm guessing you'd be able to find someone to trade with if you get the Torus 26 but then later decide it's not enough lift. Just my thoughts.

 

[orange_diver]

In your scenario, with a 26-30# wing, of which you would be using ~10# max to offset the gas in your tank, you'd still have 16-20# of spare lift left to compensate for the loss of dry suit buoyancy + you could probably generate another 5# with your lungs + you can also swim up a fair bit, maybe 10-20# ? And I imagine an instantaneous and complete drysuit flood would probably be pretty rare? Maybe if you jump in with an open drysuit by accident? In addition, you could carry a lift bag or SMB to generate another X# pounds of lift for emergencies (though deploying it in an emergency might be tricky - but you can always practice super fast emergency deployments). Also, you can also put some of your weight on the good old weightbelt or some place else where it's ditchable.

Personally I would not worry about the drysuit flood. I think 40# wings are needed very rarely for rec diving, and then only by large people using thick neoprene wet- or drysuits since they have to also compensate for the loss of buoyancy caused by the compression of the neoprene. And single tank, wetsuit-wearing tech divers may also need them.



If you are thinking about the DSS torus 26 (since that's the only 26'er I know) vs. LCD 30, then I'd personally go for the torus because it's a donut and I prefer donuts. But that's just my personal preference and a lot of other people don't seem to think it matters. However, there's a lot of people who bought the LCD 30 when the Torus 26 was not yet available, so I'm guessing you'd be able to find someone to trade with if you get the Torus 26 but then later decide it's not enough lift. Just my thoughts.

thx for your posts. you're not far off. i started this thread trying to decide between the oxycheq mach v 30 and mach v 40. patrick said that since the dimensions of the 40 were so similar i may just want to go with that one. i was trying to be even more specifc.

when you posted, it brought up the question of, hmm, maybe i can get away with less than 30, so naturally i thought of the DSS Torus 26. The Torus line was also a VERY close second to the Mach V.

So at this point it seems that i do not need more than 30# with my drysuit. to muddy the waters, tho, lets say i wanted to dive my 7mm wetsuit with my steel LP95. i use 20lb currently but that's with an AL80, so i could lose 5lb right there and be down to 15lb. A 26 or 30 would do for that as well.

is there a reason i shouldnt dive a SINGLE tank 95 steel with a wetsuit?

 

[*Floater*]

is there a reason i shouldnt dive a SINGLE tank 95 steel with a wetsuit?

No, but it would be a good idea to be able to swim it up from depth when your wetsuit has compressed and lost most of its buoyancy (say ~10-15#), your tank is still full (~10#), and you BC is empty (failure), and you've ditched your ditchable weights. Alternatively, you could use an SMB or liftbag as backup buoyancy (in open water).

However, for wing failure scenarios the size of the wing would not really matter it has failed anyway and you need to prepare for the worst case scenario that it would be completely empty. In practice it might matter depending on the location of the punctured/failure since non-bungeed wings can trap a good bit of gas and a bigger wing can trap more gas. So if you have a puncture at the bottom, then you just go vertical and you can still fill the wing almost full, but if the leak is at the top then you can't swim up without all the gas leaking out (you could try to ascent feet first), and if the elbow or corrugated hose fails then you can't even add more gas to the wing.

 

[*Floater*]

when you posted, it brought up the question of, hmm, maybe i can get away with less than 30, so naturally i thought of the DSS Torus 26. The Torus line was also a VERY close second to the Mach V.

Don't get too caught up in the numbers. Oxycheq and DSS use a different method to determine their nominal wing lift. The 30# Mach V actually holds up to about 32# worth of gas when not restricted, call this free lift. When mounted to a plate it may give you maybe 25-30# depending on your rig (plate profile, tank size and STA type if any). DSS on the other hand mounts the wing to their plate first with a 8" diameter tank on top and then tests the lift. I don't know the free lift for the Torus 26, but it may well be about the same as the Mach V since the LCD 30 is roughly 37#.

For more details, see this thread, pages 2-4. The numbers and my estimates above are based on it.

 

[Web Monkey]

i'm trying to figure out how big a wing i need to dive my drysuit and a single steel faber LP. i don't have one currently but will be purchasing a SS bp/w with hog harness. this is for socal ocean dives. i'd love to be able to get away with a 30# wing, but think i may need 40#.

The drysuit is irrelevant, since you need enough lift to bring you up even if the suit is completely flooded.

It would really suck to die because of a torn suit or seal.

Depending on which tank you pick, it can range between around 8 and 11 lbs negative (95 - 100 Cu ft Faber tanks), then add in whatever you BP is, and any other stuff you'll be carrying, plus whatever extra you want for floating on the surface

FWIW, I like to have extra lift available. You never know when you're going to need it, or might want more buoyancy on the surface.

I'd never dive anything that had less than 60lbs lift, and 75 would make me happier.

Terry

 

[ChrisA]

let's say i need 15 lb in the pool, how does that correlate to lb needed in the ocean given that salt affects buoyancy? is there a simple calculation, i.e. add 10%?

thx for all replies everybody...

Yes. The difference in lead is 2.5% of your TOTAL weight. That total is you and all your gear dive lights and all. Remember you displace your weight in water and saltwater is about 2.5% more dense than fresh water This works out to 5 or 6 pounds for many people.

You really have to do the weight check in the ocean at 15 feet depth with a near empty tank. Just go to the beach with a few pounds to much and hover over the sand at 15 feet. Take out a weight and place it on the sand. See if you can still hover. If the viz is bad and you do not want to loose the weight hend them to your buddy.

I just did this myself this morning. I only had about 2 pounds to much.

One more complication. I've found that if I'm cold I can add a couple pounds of lead and this will allow me a larger air space (less squeeze)

 

[SparticleBrane]

I dive Worthington 95s

When did you make the switch from 72s to 95s?!