Venting dry suit fact or myth.

[mister p]

Originally Posted by dally

"On this note, I am qualified "
as what exactly MrP ??

O level? Driving Licence? aaah "note", I have a Grade 1 Theory in music

[kerny]

Originally Posted by biffer

The easiest thing to do as suggest is squat with your fingers in your neck seal. You don't want excess air in the suit if your wearing a life jacket
When you're diving air shift to legs can be a problem in the not so well trained and I've seen uncontrolled accents from depth and it ain't pretty.
Just get the air out to be on the safe side

sent from a remote device

That's two of you now who have mentioned from personal experience seeing uncontrolled accent with air shift to the legs in dry suits.

[dally]

Quote:
Originally Posted by dally
"On this note, I am qualified "
as what exactly MrP ??

O level? Driving Licence? aaah "note", I have a Grade 1 Theory in music

you posted it, thought you might know,
obviously your advice on matters sub-aqua is something to be taken very seriously then.

[Pikey Dave]

Originally Posted by kerny

That's two of you now who have mentioned from personal experience seeing uncontrolled accent with air shift to the legs in dry suits.

Aye & since when did personal experience count against armchair experts & sceptics

[mister p]

Lighten up a smidge Dally. If you look at my LR Defender opinions you'll see that everything is very serious indeed.
But it all depends on what it is that you're after Dally. My posts were based on personal military, instructing PADI (admittedly not the highest echelon of s.a.) and RNLI experience.
My ribbing nowadays is purely leisure and as such I respond in a leisurely manner, but the threads which touch on safety I trust are treated with a little less levity and focus on members' invaluable and broad blend of experience. This is why we're all here. To share, deduce and discover.
What was it you were after Dally?

[kerny]

Originally Posted by Pikey Dave

Aye & since when did personal experience count against armchair experts & sceptics

It probably will!! but only if one of them ever experience anything like this....

[biffer]

to watch an upside uncontrolled accent is bad, you have to be real quick to stop it, just trying to reach upside down into a hole can start it off.
let see if i can get this right after all these years, what ever air you have in your suit will compress by half by the time you hit 10m, so to get your bouyancy right you add some more air to compensate, every 10m more you go down it halves again and so on.
if you go ballistic at 20m short of putting a hole in your drysuit you will not fin against the air expansion and lift it provides.
if you could drag a five gallon can to 30m it would only be a quarter of its size, like wise on the way up a five gallon can would probably explode as would your lungs and drysuit seals as the air quadruples in volume.
after all these years of diving i still wear ankle weights when sport diving, being feet light and losing my mask was always my pet hate

[mister p]

Originally Posted by biffer

to watch an upside uncontrolled accent is bad, you have to be real quick to stop it, just trying to reach upside down into a hole can start it off.
let see if i can get this right after all these years, what ever air you have in your suit will compress by half by the time you hit 10m, so to get your bouyancy right you add some more air to compensate, every 10m more you go down it halves again and so on.
if you go ballistic at 20m short of putting a hole in your drysuit you will not fin against the air expansion and lift it provides.
if you could drag a five gallon can to 30m it would only be a quarter of its size, like wise on the way up a five gallon can would probably explode as would your lungs and drysuit seals as the air quadruples in volume.
after all these years of diving i still wear ankle weights when sport diving, being feet light and losing my mask was always my pet hate

As I said earlier, I'm feet light too and wear weights. This whole bobbing about the wrong way up sends shivers down my spine. And that's even when I know about it, am expecting it, am trained to overcome it and have the kit to survive it.
Imagine if it came as a rather ugly, if quick, surprise.

[kerny]

In my kayaking days,we were taught to always to vent our dry suits because of the issue of air getting into the legs which could force your head under the surface. My personal thoughts on this, and they are not (scuba diving related) are YES... but more so... if wearing a BA, most of them are 50n and they do lose some buoyancy after a certain amount of time, unlike L J's. Also, as previously stated BA fit tight around the chest so there is more room for air in the legs. Now if you are wearing a LJ I don't think that would be an issue due to an inflated L J keeping your head and shoulders somewhat higher out of the water because of the extra buoyancy especially in the chop, now this is only my opinion. I do believe there was a video out on youtube some years back allegedly proving this theory wrong, but I can't find it, maybe it's been taken off.

[Mr Flibble]

Originally Posted by captnjack

You won't naturally hang head down. The natural position even without any kind of life jacket will be flat, either face down or face up. Just because some gas was pushed out of your torso does not make your chest negative/sink. There's still a good amount of positive bouyancy up there with your lungs and residual gas in the suit. It may take some time to shift flat way naturally or you can just help it along by doing a "situp" which is the the same as this ball curling motion. Its not at all difficult or unnatural.

Captnjack is indeed correct. Your whole body wearing a drysuit (neo or membrane) is positively bouyant, the fact that most of the air is in the feet doesn't mean the rest of the body sinks just means the feet sit higher, you will float horizontal even entering the water head first. If it wasn't the case I wouldn't be here. To test, put on a drysuit and float head up. To keep this attitude you have to splay legs and arms. Put your arms and legs together at your side and you'll go horizontal, usually face down as your knees tend to bend slightly. 30 years of drysuit diving wearing more neo and membrane suits than I care to remember. Anyone experiencing different must have a head full of cement.

Inverting whilst diving can cause a bouyant ascent because of compressed gas expanding at the feet. This is a different scenario as scuba equipment generally makes the body top heavy (or bottom when inverted).

Fire a Delayed SMB from depth, it'll hit the surface vertical,if not under tension it'll lay flay on the surface, by somes reckoning it should stay vertical, it doesn't.

[Richard Selman]

Happened to me once on one of my first dives after qualifying. Trying to stay horizontal at 20m but the air ran up my legs and inverted me. Started to accelerate upwards but caught it about 5m. Got a bit of a scare but swam back down to depth to recompress. Just inexperience making me slow to react. Dead easy to get confused in all the bubbles. Once you know the feeling all it takes to correct it is a bit of gentle finning.

On the cat I suck out all the air before we set off to minimise the buoyancy in case we go for a swim. Either I wade in to neck level and break the neck seal with a finger or I pull the seal over my top lip and suck out all the air until I'm vacuum packed.

Offshore survival suits used to have a zip up section on the legs to tighten it in. Now they have ankle relief valves.

[biffer]

Let go a delayed smb. You can hit the surface from 30 m in under a minute. Where will you get the time to do that

sent from a remote device

[Nos4r2]

Wearing my surface drysuit, I came perilously close to what felt like inverting at the Priory Bay picnic the first year I had this particular drysuit.

I went for a swim from the beach in it without venting it properly and as I was on my face, all the air went to the legs and my head went under.
I may be wrong, as it was easily recoverable-I was in 3 feet of water so I just stuck my hands on the bottom and pulled my feet under me. I've made sure it's vented properly since.

The way I see it is if I go overboard at speed,I don't need the possibility to add to my worries.

[Ian M]

Originally Posted by Mr Flibble

Fire a Delayed SMB from depth, it'll hit the surface vertical,if not under tension it'll lay flay on the surface, by somes reckoning it should stay vertical, it doesn't.

Have I missed something What has a delayed SMB got to do with drysuit venting?
If you want to keep you SMB vertical ensure that you are slightlly negatively bouyant when ascending and winding in, although I have never felt the need. I guess it depends on just how switched on you surface cover is.

[Mr Flibble]

Originally Posted by Ian M

Have I missed something What has a delayed SMB got to do with drysuit venting?
If you want to keep you SMB vertical ensure that you are slightlly negatively bouyant when ascending and winding in, although I have never felt the need. I guess it depends on just how switched on you surface cover is.

Yes you have.
Discussion was about jumping in head first off a RIB with air in drysuit. Would you stay inverted? I was merely pointing out to those that claim you do that if that were the case then a DSMB (which like a drysuit is essentially a bag with air in it) would act in the same manner, ie as it ascends vertically it would stay vertical when it breaks the surface, it doesn't it lays flat on the surface as the whole device has bouyancy. To keep it vertical you either attach a weight to the bottom or act as the weight yourself. A drysuit will act in exactly the same manner. Physics is physics. To keep a drysuit fully inverted you would need to either attach a weight to your head (to counteract the natural bouyancy of head, lungs etc) or stay completely vertical so that all the bouyant force is acting on the highest point of the drysuit (the feet), any deviation from this will result in bouyancy lifting. When snorkelling, I've hauled myself down a weighted line in my drysuit, let go and did a rapid ascent feet first. I hit the surface feet first then end up floating horizontally (usually face down) and don't stay inverted and drown. In answer to the OP's question. You tend to bend your knees slighty when lying flat/face down, this raises your feet higher than your head and will result in a slight head down attitude when floating on the surface but doesn't cause full invertion. Drysuit wearers should become adept at moving/swimming in their suits as without fins on face forward swimming is usually with hands alone.

[Mr Flibble]

Originally Posted by biffer

Let go a delayed smb. You can hit the surface from 30 m in under a minute. Where will you get the time to do that

sent from a remote device

Sorry I don't get your point here. I frequently use delayed SMB's. They are designed to be used from depth.

[biffer]

Sorry I thought we firstly was talking about venting suits and then slightly hijacked the post by explaining about Boyles law. Ie the compression of gasses under pressure.
The only way I could read your post in this instance was to think that you were looking at deploying a DSMB while you were heading for the surface like a Polaris misslie

sent from a remote device

[mick]

These will keep your feet pointing down

[Steve_B]

Only once got caught out.

Working on a heavy chain in Faslane, Scotland, the exercise was to saw through a 2 inch link. Got so tired and frustrated, feet went higher than body and got inverted. Fortunately was neutrally bouyant and was able to roll back upright.

Had to buy the beers that evening back in the mess though ....

[captnjack]

To the OP and any others, practice swimming in your drysuit. Vented, unvented, with and without a lifejacket. It doesn't take long to get comfortablewhich is really what this is all about. That way when you do go ass over tea kettle out of the boat you'll have the experience and skills to cope with your shocking immersion.