Water neutrally buoyant?

[fisherdvm]

I bought a used drysuit. Took it to a diveshop to have neck seal replaced. He said, the suit is too old (it is supposed to be a brand new, never used, but aged suit) and he does not want to replace the seal. Anyhow, he said if it leaks, I would "sink like a rock".

So, did I miss something in physics? He said he has taught "thousands" to dive, and has been teaching divers for 25 years. He said that a wet drysuit would weight hundreds of pounds as the liner would take up water. I don't argue with that...

But isn't water neutrally buoyant? So I could lug along an extra 200 lbs of water, and my buoyancy would be the same as on the surface? All I have to do is inflate my BC, and as long as I am not overweighted at the surface due to excess air in my drysuit, I should not have any problem surfacing, right??

If my BC has a buoyancy of 28#, and I carry less than 28#, I should have no problem surfacing, right? If I dump my weight, and even if my BC did not function, I would still be neutrally buoyant - right.... Assuming that my tank is roughly neutrally buoyant?

I should not be sinking like a rock with a wet drysuit, right?

 

[JeffG]

I bought a used drysuit. Took it to a diveshop to have neck seal replaced. He said, the suit is too old (it is supposed to be a brand new, never used, but aged suit) and he does not want to replace the seal. Anyhow, he said if it leaks, I would "sink like a rock".

So, did I miss something in physics? He said he has taught "thousands" to dive, and has been teaching divers for 25 years. He said that a wet drysuit would weight hundreds of pounds as the liner would take up water. I don't argue with that...

But isn't water neutrally buoyant? So I could lug along an extra 200 lbs of water, and my buoyancy would be the same as on the surface? All I have to do is inflate my BC, and as long as I am not overweighted at the surface due to excess air in my drysuit, I should not have any problem surfacing, right??

If my BC has a buoyancy of 28#, and I carry less than 28#, I should have no problem surfacing, right? If I dump my weight, and even if my BC did not function, I would still be neutrally buoyant - right.... Assuming that my tank is roughly neutrally buoyant?

I should not be sinking like a rock with a wet drysuit, right?

Well, the grain of truth to his story is that...maybe your undergarments will lose its ability to hold gas within it fibers. If you lose that gas you will become more negatively buoyant.

This is why buying the correct type of undergarments for a drysuit is important.

 

[PhilEllis]

I bought a used drysuit. Took it to a diveshop to have neck seal replaced. He said, the suit is too old (it is supposed to be a brand new, never used, but aged suit) and he does not want to replace the seal. Anyhow, he said if it leaks, I would "sink like a rock".

So, did I miss something in physics? He said he has taught "thousands" to dive, and has been teaching divers for 25 years. He said that a wet drysuit would weight hundreds of pounds as the liner would take up water. I don't argue with that...

But isn't water neutrally buoyant? So I could lug along an extra 200 lbs of water, and my buoyancy would be the same as on the surface? All I have to do is inflate my BC, and as long as I am not overweighted at the surface due to excess air in my drysuit, I should not have any problem surfacing, right??

If my BC has a buoyancy of 28#, and I carry less than 28#, I should have no problem surfacing, right? If I dump my weight, and even if my BC did not function, I would still be neutrally buoyant - right.... Assuming that my tank is roughly neutrally buoyant?

I should not be sinking like a rock with a wet drysuit, right?

Your dive shop guy is probably a very nice guy and probably knows a great deal about scuba diving, teaching scuba diving, and the like. But on this issue is is both confused and wrong.

Water in your drysuit has no impact on buoyancy, except to the extent that it might displace some air necessary for neutral buoyancy. If you obtain neutral buoyancy with no air in your drysuit, and the suit completely floods, you still have neutral buoyancy.

Now, getting out of the water with a suit full of water is another issue. Thanks.

Phil Ellis

 

[fisherdvm]

This reminds me of the USCG Lt who drowned because she and her buddy had 60 lbs of weight in ther BC. The BC was not hooked up to the tank, and they both drowned due to rapid descent and excessive depth....

Maybe the instructor is trying to reflect on this tragic accident... The moral of the story, maybe is not to exceed the buoyancy of your BC with weight that you can't ditch.

 

[MikeFerrara]

Well...yes and no.
Dry underclothes in a dry suit (I made a funny) hold quit a bit of air and can be pretty buoyant. to counter that you add balast to get neutral. If the suit completely floods and the air isn't in the suit it will be neutral...yes water is neutrally buoyanct in water...bet you straped on all that lead because of the air that used to be in your dry suit. Now you can be pretty negative. Certainly a dry suit that is full of water would be very heavy on land.

That said, most leaks don't really cause a full flood and the suit will still hold some air. I even had a zipper pull part way open on a dive and it didn't completely flood the suit. I doubt there are many dry suit divers who have done many dry suit dives without getting pretty wet a time or two.

If I were the OP, I'd buy the seal and replace it myself.

 

[webjr]

Your theory is correct. The real world may be slightly different depending on where and how bad the leak is. Even when fully deflated there is still probably a small amount of air in the drysuit. That is compensated for during you weighting process. If the leak was very large and in a place where ALL air was removed from the suit (like a major neckseal blowout)you could go slightly negative. If you weighted yourself properly with as much air as possible removed from the suit the difference should be very slight though.

 

[spectrum]

I think MikeFerrara has the right idea.

If you are wearing significant undergarments you have an amount of loft that stays with you while diving, especially in the shallows where your weighting is determined. That loft defines some air space. Since it's there you need to wear an amount of weight to counteract it. That airspace will fill with water in a flood. In doing so you will have lost some relatively static buoyancy while still wearing all of your lead.

If you were to wear a drysuit and allow it to squeeze for a close fit with no garments then a flood would not change your buoyancy in a perfect world.

Pete

 

[Walter]

Water is neutrally buoyant, but when you take a neutrally buoyant system and replace a postively buoyant componet with a neutrally buoyant componet, the net result is you'll sink like a rock.

 

[Gilldiver]

The very worst case would be a tri-lam or rubber suit with a full neck seal rip resulting in a total flood and wearing 400 gram underwear. The amount of weight needed to sink 400 gram underwear on a 6'+ person can be up to 30 pounds due to the amount of air needed to loft the underwear properly.

In the above you will be negative by just about what is on your weight belt. So you would need to drop it. That solves the first problem. But just because you are neutral, dosen't mean you will not have to work hard to get up.

Weight is not Mass - (a 3,000 ton nuclear sub is neutral at depth by no one on this board will be moving one by themselves), with a flooded suit you will now be moving all that water that is in the suit along with your gear. If the water is cold you will get tired real quick.

Once you get to the surface, you need to get out and a fully flooded suit is quite heavy out of the water, you will need to cut both legs at the ankel to drain it.

All this being said, I have never seen a fully flooded suit - I'v seen them quite full and had to cut ankels once for a diver, but never fully flooded.

As for your suit, if the LDS will not do it, there are a few good dry suit shops that you can send it to. The cost of UPS shipment is many times offset by the reduction in price from a shop that specializes in repairing suits.They will evaluate it and call you before doing the repair, so in the worst case you are out only on way shipping (plus what you paid for the suit).

 

[captain]

Have the boat crew pull you aboard by the feet, that way you can drain it at the neck.