Drysuit diving - uncontrolled accend

[tobiaslindgreen]

Hey ScubaBoard

I just bought my new (and first) drysuit and have been teached and tried it in a swimming pool.

The descend is ok and my buoyancy is somewhat ok at the bottom (3-4 meters/10-13 feet).
However, when i am horizontal at the bottom and try to go vertical (knee standing on the bottom),
i suddenly become very positive buoyant and can't manage to vent the suit before getting to the surface.

Therefore, i am quite nervous about, whether or not i can do a safe accend and go to the safety stop.

How to prevent this and why does it happen?

Best regards!

 

[chrisch]

Stop using the suit as a BC and use the BC as the BC. Leave the auto dump fully open. Only add a little gas to the suit to counter the squeeze as you get deeper. You should not need to add any gas at all for 3-4m.

 

[Johanan]

When you get on your knees from the bottom, your shoulders rise. The air in the suit travels to the highest point and expands. This is why you became more buoyant. In a dry suit you must think ahead and vent a bit of air beforehand. And it is good to keep the exhaust valve open or almost open. It will vent some of the air automatically. IMHO there is no problem using the suit for buoyancy.

 

[Rusty Roo]

if you can master buoyancy in a pool you can do it in the sea / lake.

 

[Patoux01]

if you can master buoyancy in a pool you can do it in the sea / lake.

Yeah, or maybe not. Surge, anyone? Diving in some areas is as shallow as a pool (3m dives), but when you get 1m surge above you, it's really not "if you can do it in a pool you can do it there".

Anyway, on topic:
- don't use the thing as a BC
- don't put your knees on the ground
- keep the dump valve fully open (or almost)
- remember to breathe out as soon as you notice you're ascending when you don't want to
- make sure you're not kicking yourself up if for some reason you're getting out of trim

 

[tobiaslindgreen]

I think it would be better for me to learn doing BC with the drysuit before having to handle two air sources. I been told not to use the BCD for BC.


When you guys ascend, are you horizontal in the water? Or vertical?

Thanks for the answers!

 

[Searcaigh]

I ascend horizontally, you want to be de-gassing all of your tissues at the same level as you ascend.

 

[CptTightPants21]

You should be ascending horizontally.

A horizontal body position creates the most drag, which slows down the speed of your ascent and decent (see skydivers). When you go vertical you are reducing the drag that your body is creating and becoming more buoyant. It is causing you to ascend a few feet, that in conjunction with Boyle's law and you being in such a shallow depth to begin with is causing you to end up on the surface.

There are different ways to run a drysuit. I run it with a combination of air in suit/air in BC; more than the "just take off the squeeze" some folks suggest, but it is definitely not my only source of buoyancy. I generally follow the equalize the ears, equalize the suit (give it a quick puff of air) philosophy and I'll add air to the BC based on my experience/feel for how fast I am ascending, how much air is in the suit, etc. How you run a drysuit is a personal preference and takes experimentation and experience. You need to learn to anticipate the changes and vent preemptively because by the time you really need to vent, it will be too late.

 

[Dhboner]

First off there should never be a need to go vertical "knees standing on the bottom" but that's a whole other thread. Firstly just put enough air in the drysuit to eliminate squeeze and allow the undergarment to do it's job. Don't use your drysuit for buoyancy (in an emergency like a wing failure it will provide all the lift you need but that is not it's purpose). Once you are ready to ascend begin to vent the suit by raising the exhaust valve to the highest point (usually a chicken wing maneuver). That way excess air is on it's way out before it becomes a problem on the ascent. If you feel squeeze it will be brief since you are ascending. Continue to vent air regularly as you ascend (even if it means stopping briefly) and try to avoid going vertical...go vertical and all the lift moves to your upper body and can seriously increase your rate of ascent.

 

[undrwater]

Where's your exhaust valve? A lot of good advice here. Assuming you want to go vertical for some functional purpose, get started venting right away, not after the fact.