Drysuit diving without enough weight. Dangerous !!

[lamont]

I had added a tiny blast of air into the suit to reduce some squeeze just before the great fly away occured. This is how the whole thing started.

I was having trouble venting from the rental suit because it was a rear entry model and the exhaust valve was almost in my armpit area. Not a very smart place to put an exhaust valve IMO.

The air I let out of my suit was partly a result of doing this, and it expanded on the way up as expected. I just couldn't vent it fast enough using conventional methods.. especially since I was travelling faster than air by this time.. ;-) Octopus was freeflowing, air was shooting out of tank, tank was getting lighter and I was fooked. ;-)

I can tell you it was an odd feeling.. kinda fun actually (of course, not safe).

Things I have to do as a result of this include;

- fix octopus to prevent freeflow, or replace it entirely.
- increase weight to 40 lbs. test with nearly empty tank.
- ankle weights to keep feet down.

are you sure you didn't just have an air bubble in your feet?

if you're diving an aluminum tank with 40# around your waist, that configuration should drag your butt down. if your feet are going up, then either you have extremely buoyant feet or else you've got a big air pocket down there in your drysuit.

its pretty normal for beginning drysuit divers to not have any idea of how much air is in their drysuit and to blame buoyancy issues on being underweighted.

and adding weight will actually make you have to compensate by adding more air, which will expand with depth changes more and will cause more buoyancy instability and runaways underwater. less weight will actually make you more stable.

- accept some squeeze rather than risk floating off to never never land.
- use BC for buoyancy control
- use a drysuit with an exhaust valve in a semi intelligent location.

 

[Laser]

and adding weight will actually make you have to compensate by adding more air, which will expand with depth changes more and will cause more buoyancy instability and runaways underwater. less weight will actually make you more stable.

Spot on advice in my opinion.

 

[Mike Newman]

Depends on what size of tank you are using. If i remember right a standard aluminum 80 holds about 6lbs of air which means you will be 6lbs heavy at the beginning of your dive and neutral with a near empty tank if you are properly weighted.

Were you using a trilam or neoprene type drysuit. I would think 32lbs would be plenty with a trilam suit.

I'm sorry, but this is a common mistake. Your tank type and size has little to do with the weight of the air it contains and the fact that, when you expend it (in an open circuit Scuba system), you become more positively buoyant.

The buoyancy characteristics of tanks affect only the overall calculation of weight required. Whether a tank, in isolation, is negative or positive at about 500 psi is largely irrelevant - though one that does not become markedly positive does allow you to carry less removable weight.

 

[Mike Newman]

Having used both BC and drysuit for buoyancy im firmly convinced that a properly weighted single cylinder diver with a properly fitting drysuit can quite happily use either as a source of buoyancy and its down to personal preference.

Frankly though, if you start using your BC, which I acknowledge many experienced divers prefer to do, you're not actually selecting 'either'. You are selecting both - since you have to add air to your drysuit to avoid squeeze as you descend. Not an issue if your suit vents air automatically and reliably during the ascent, but if it doesn't, you're now juggling two buoyancy aids.

This may well be why the Training Agencies recommend and teach using the drysuit underwater and the BC for surface buoyancy only.

 

[The Kraken]

Hey, Mike,

Check the date of the last post !!!

the K