The buoyancy of 7mm wetsuit

[cast]

Does any expert know normally how many lb positive an average 7mm wetsuit would be?

I heard that it will become neutral or even negative at the certain depth. But how deep? Is there any experiement data available? I can't find any on the internet.

Any help would be greatly appreciated!

 

[DA Aquamaster]

In my experience, a 7mm suit is around 15-22 lbs positive at the surface depending on the size of the suit and whether it is a one piece or a famer john.

All neoprene is not created equal and it varies a lot in terms of how a particular blend compresses, how well it holds up and snaps back overtime, how stretchy it is and how well it insulates, so experimental data is very dependent on the specific neoprene used and not very generalizable to neoprene wetsuits as a whole.

But in general it is not uncommon for a 7 mm suit to be compressed to around 3 mm at 100 ft.

 

[pasley]

Weigh the suit, for a 7 mil suit is shoulb be about 1 pound of suit equals 3 pounds of lead at 1ATA. Yes, as you go deeper the suit will compress, which is why we wear a BC to compensate for the loss of bouancy at depth. My wetsuit needs 18 pounds by itself, plus the AL80 tank and then me.

 

[cast]

Thanks.
I am still curious how much buoyancy it will loss at around 100-130 feet underwater. Sounds like lossing 15lb is reasonable, plus the 8-9lb air. BC with 25lb lift seems able to overcome these weight change. Why do a lot of people need 40+lb BC or wings for the single tank?

 

[DA Aquamaster]

25 lbs is sometimes not quite enough lift to get a diver comfortably bouyant at the surface when they are configured for cold water diving. It's a personal preference kind of thing.

 

[donacheson]

Does any expert know normally how many lb positive an average 7mm wetsuit would be?

I heard that it will become neutral or even negative at the certain depth. But how deep? Is there any experiement data available? I can't find any on the internet.

Any help would be greatly appreciated!

My 1/4-inch wetsuit is made up of about 3000 square inches of closed-cell neoprene foam. That’s about 750 cubic inches of foam. It weighs about 9 pounds and would displace about 62.4(750/1728) =27 pounds of fresh water if uncompressed.
Hence, on the surface, it’s about 18 pounds light.

Based on some data on one specific neoprene foam, probably not the one my wet suit is made of, at 20 feet it would be about 12.5 pounds light; at 40 feet, about 8.5 pounds light; at 60 feet, about 4.5 pound light; and at 100 feet, about 1 pound heavy.

 

[pasley]

... Why do a lot of people need 40+lb BC or wings for the single tank?

They probably don't need all that lift or else they are badly over weighted. Some, as has been mentioned want the extra list to get them higher out of the water on the surface.

 

[xSandman3]

My instructor taught us to start with 10% of our body weight, then add 6 lbs. for salt water when weighting ourselves for 7mm wetsuits. This calculation is right on for me. Any more and I sink like a brick, any less and I have to swim down the first 10 feet untill the suit compresses.

 

[O2BBubbleFree]

I like to be slightly negative to start.

Since most of the compression (and buoyancy change) seems to take place in the first 15 feet or so, I find that if I start out neutral then I can have a heck of a time maintaining my safety stop. Especially when I was diving at Lake Tahoe (higher altitude, so shallower safety stop) with an aluminum tank (positive @ 500psi). Due to the combination of those three, I've seen several divers pop to the top when trying to do their safety stop.

Granted, most people don't do high altitude diving, so one of the three factors won't be an issue.

 

[redacted]

Weigh the suit ... 1 pound of suit equals 3 pounds of lead at 1ATA.

Very interesting and useful relationship - Thanks