New Tech Kit

[Prometheus]

CDNN Iron Knight wreck.?alsohttp://www.rebreatherworld.com/rebreather-accidents-incidents/15088-fatal-diving-accident-updated.html

[nigelH]

Originally Posted by Mark Chase

An australian diver was lost to us a couple of weeks ago. He passed out on decent. His buddies found him on the bottom but were unable to obtain positive boyancy and lift the body.

I read that report too and wondered why.

I doubt it was his wing size that was the problem but if a report ever materialises, and they rarely do, we will see. He was a well liked moderator on RBW so I prefer not to speculate.

[ianfirmin]

Originally Posted by nigelH

The world's most obese diver would need masses of lead not masses of lift.

94lbs of lift is for people who don't understand diving. 50lbs (24Kgs) is realistic for any dive kit. By the time you are carrying twin 18s and two 15L stages so much of your gas is helium you need less lift rather than more.

Nigel is probably correct but does not explain why. Human bodies are close to neutrally buoyant. A large body is surrounded by a large buoyant suit (wet or dry) that needs more weight to maintain neutral buoyancy. However, and I'm guessing here, I wouldn't expect the difference to be much more than 6kg between the typical small person and the typical very large person.

What you need adjustable buoyancy for is the weight of gas you are carrying. To be able to use all of the gas in your cylinders you need to be neutrally buoyant with empty tanks. Thus, with full tanks, you need extra buoyancy at the start of the dive. Using rough figures for air, your 12l tank at 232bar contains 3.3kg of air. Thus, when you start your dive (perfectly weighted) you need 3.3kg of buoyancy to maintain trim. At another extreme, you may have a triplet of 20 litre tanks and a couple of 12 litre stages. This amount of gas weighs 23.4kg. Now, say you are the careful type and would like to ensure you have sufficient buoyancy in the case of a drysuit flood you might need another 6kg of buoyancy. Thus, total buoyancy requirement is in the region of 30kg (66 lbs).

Now. There could be the case that you are carrying so much kit, wrecking bars, tools, torch batteries etc that you are negatively buoyant at zero bar gas without any extra weight. You need to add this to your buoyancy requirement. Even so, I must admit that a 90lb lift wing seems overkill for virtually any "normal" dive.

One corollary of this is a refutation of the concept of just using a drysuit for buoyancy adjustments. Even a single 15l of air has a potential buoyancy change of over 4kg. I would hate to dive with an extra 4 litres of air in my drysuit.

One final point. All the figures above relate to air and the same volume of helium weighs a lot less.

ATB
Ian

[David D]

I've had my OMS 100lb single-inflator wing, S/S backplate, IQ harness, and steel 12ltr twinset for a few years now.

The wing is very durable. The inflator is getting finicky, probably just needs a service. If you intend to dive the wing with wetsuit at any time in the future, get the dual inflator (see below).

The harness has a design flaw in my opinion. The shoulder D-rings can't be dropped lower than the pinch clips, which are positioned quite high on the chest. This means that stage cylinders sit marginally too high for my liking. I get round that by using a longer loop on the neck of the stage cylinder. I'd prefer a more easily adjustable harness.

As to the amount of lift, I took the harness and wing to the Red Sea last month and dived with four aluminium twelve liter cylinders on a wall. Without that amount of lift at the start of the dive, I would have sunk like a stone. I'd rather have and not need it than need it and not have it.

My twinset is faber steel with MDE manifold. Very nice set. Can't comment on Euro cylinders though they seem to be getting a few mentions recently.

[MarkP]

Originally Posted by David D

I've had my OMS 100lb single-inflator wing, S/S backplate, IQ harness, and steel 12ltr twinset for a few years now.
<snip>
As to the amount of lift, I took the harness and wing to the Red Sea last month and dived with four aluminium twelve liter cylinders on a wall. Without that amount of lift at the start of the dive, I would have sunk like a stone. I'd rather have and not need it than need it and not have it.

I'm afraid I just don't understand why. Assuming worst case, let's say you're not diving He and you're wearing a neoprene suit, that's approximately 12Kg of gas at the start of the dive. Another 4Kg for suit compression and you should start the dive 16Kg negative. I reckon a whole 16Kg lift should keep you on the surface. Add a few more to keep your face nicely out of the water and you're looking at a 50lb lift wing, max.

I simply don't see the need for more than that.

[neilh]

Twin 12L 232s is a pretty standard choice. When choosing between Fabers or ECS/Euros I'd suggest seeing if you can try some and find out what you feel more comfortable with. Also what do your buddies dive? If you dive the same type then at least you'll be able to borrow kit without too much hassle

Personally I dive a Halcyon Evolve wing with a basic backplate and one piece harness. It's not everyone's cup of tea so I'd definitely recommend trying it to see if you get on with it before deciding to go that way.

Originally Posted by Mark Chase

An australian diver was lost to us a couple of weeks ago. He passed out on decent. His buddies found him on the bottom but were unable to obtain positive boyancy and lift the body.

I reckon a 90lb lift wing would have done it

I think it's hard to speculate without knowing the facts here. I find it difficult to see how you would be unable to ditch a weight belt and any stages from someone and them still be negative with a full wing and suit. Surely that would need to have been a completely inappropriate wing in that case? Perhaps the wing had holed or the inflator had failed or he'd had a full suit flood? If the wing or inflator had failed then the amount of lift would be irrelevant if you can't use any of it.

[David D]

Originally Posted by MarkP

I'm afraid I just don't understand why. Assuming worst case, let's say you're not diving He and you're wearing a neoprene suit, that's approximately 12Kg of gas at the start of the dive. Another 4Kg for suit compression and you should start the dive 16Kg negative. I reckon a whole 16Kg lift should keep you on the surface. Add a few more to keep your face nicely out of the water and you're looking at a 50lb lift wing, max.

I simply don't see the need for more than that.

I can't give you the specific weight of the gas. I can tell you I had a S/S BP and another 8kg (possibly 10kg, can't remember) of lead. 6kg for the twinset then another 1kg (or 2kg) for each stage. Weight checked twice with all four cylinders virtually empty. I will admit that I didn't spend an age getting this exact, but 1 to 2kg extra per 12 ltr stage seemed correct at the time.

By the time I'd reached max depth the wing was blown up like a baloon. Angling my head back I could feel the wing pumped up with a lot more gas than I've ever used before. By the end of the dive with the twinset down to 30ish bar and the stages getting bouyant, the wing was much more compact.

Like I said, I'd rather have it and not need it than need it and not have it, and I reckon I needed it on that dive.

[Twinsetmad]

Originally Posted by MarkP

I simply don't see the need for more than that.

Hi Mark your right... I will probably never need that much lift...ever..

But if the wing is bungied it doesn't matter... If I want to use on 10lb of lift then fine... I just inflate it that much...the rest stays compact and in place creating very little drag...

Then again.. if I feel the need to lift a cannon.. I jus hold on and blow it up

[Clare Gledhill]

But if the wing is bungied it doesn't matter... If I want to use on 10lb of lift then fine... I just inflate it that much...the rest stays compact and in place creating very little drag...

Until you have a runaway inflator....

Arguments against/for bungied wings have been done to death on here and I won't waste bandwidth adding to them on this thread. But it is simply not the case that you can never have too much lift capacity.

And if you really needed 100lbs of lift to carry 4 ali cylinders you have very serious weighting issues indeed. I've carried 6 full of nitrox plus a twinset on a 40lb wing. No issues really although for a sea dive I would have preferred a 55 lb to get a little higher out of the water on the surface. 100lb is roughly double what was needed.

[David D]

Originally Posted by Clare Gledhill

But it is simply not the case that you can never have too much lift capacity.

In your opinion.

Originally Posted by Clare Gledhill

And if you really needed 100lbs of lift to carry 4 ali cylinders you have very serious weighting issues indeed.

I didn't say the wing was fully inflated, only that it had a lot more air in it than usual and that I was glad of the excess lift.