85m air dive

[Tortuga68]

The tighter you've got the bungees and the easier it makes venting, the more gas you'll lose if you have a problem with the wing integrity

I understand that, although the bungees aren't "tight" per se, they're installed with the wing fully inflated as per OMS guidelines; but it's a redundant bladder wing, so if I have a problem with a leak, I can switch

 

[lamont]

I understand that, although the bungees aren't "tight" per se, they're installed with the wing fully inflated as per OMS guidelines; but it's a redundant bladder wing, so if I have a problem with a leak, I can switch

Do you dive with the second inflator hooked up, or do you disconnect it to prevent auto-inflate?

 

[lamont]

I understand the principle of being neutral with empty tanks; but in practice, I usually have ~100 bar in the twins and 50+ bar in each stage by the end of my 6m stop

And what I need to be able to do is trim out at 75m plus with up to 180 bar in the twins and over 100 bar in each stage, while wearing a 3mm shorty; I'm still not seeing how 30# is going to let me do that, let alone pull up my buddy from that depth if it should be required

In a 3mm shorty I can get down and hold stops comfortably without any extra weight under the above conditions; with my 5mm hooded shorty (which I used on the 85m dive) I need a single weight, which I cable-tie to my tank bands/manifold

If you can show me the math that says 30# will work, please do

I don't speak crazy metric, but in the god-fearing american imperial system, 2xAl80 backgas is 5# swing each, one Al80 is another 5# swing and an al40 is 2.5# swing for about 17.5# of swing. The shorty will only be a few pounds which comes out to around 20# of swing.

If you can get neutral near the surface with no gas and no gas in the wing, then you've already validated that all the positive constant buoyancy in your system offsets and cancels all the negative constant buoyancy in your system. You can ignore thinking about regs and bands and manifold, etc -- whatever kind of bouyancy math you attempt to do it had better add up to zero or you wouldn't have been neutral when you tested it. All you just have to be worried about is crushing at depth and swing of the gas in the tanks.

Getting both you and your buddy up, using your buddies wing from depth with full tanks would take 40# of swing (which I'd say validates that wing size).

For double-HP130s (18L doubles?) that would add another 7.5# of gas per diver bringing the total to 55# of swing, making 60# wings a good choice for the larger tanks.

Personally I'd rather have a drysuit at those depths, even if i didn't wear any kind of a thermal layer other than something to prevent chafing on the material...

 

[Tortuga68]

Do you dive with the second inflator hooked up?

No, I don't

 

[Tortuga68]

Getting both you and your buddy up, using your buddies wing from depth with full tanks would take 40# of swing (which I'd say validates that wing size)

The scenario I'm considering is my buddy having a total wing failure; The buddy might also be unresponsive/injured and unable to fin. I have not experienced this myself, but one of my buddies has - he had to pull someone with a non-functional single-bladder wing up from ~60m

Anyway it seems we agree that 30# would be insufficient for this purpose

Personally I'd rather have a drysuit at those depths, even if i didn't wear any kind of a thermal layer other than something to prevent chafing on the material...

Because you prefer a drysuit for redundant lift?

 

[DaleC]

I dive both double Al80's and St72's with a 32# wing and find it adequate for the task. However, I do have about 16#'s of ditchable weight in 8# increments, a DS and a 50# LB.

Can't recall in your case Tortuga what weight you were carrying or whether it was ditchable?

*Edit* I see the answer in post 170.

 

[lamont]

Because you prefer a drysuit for redundant lift?

it is also depth-compensating because you add gas as you go down compared to the inherent crush of a wetsuit which does not help you out at all.

that can be partially lost on a dive, but its an unlikely issue to have in conjunction with other problems.

 

[ianr33]

I'm going to disagree with the need for a drysuit. I've done maybe 20 dives to 200 feet (60m) in a ratty old 3mm wetsuit. If the watar temp is in the 80's its perfectly warm enough ( I'm a W.W.W.!) and the buoyancy swing is negligible.

At Tekweek in Cayman a couple of years ago people were doing 300 foot dives in shorts and T shirts.

With water in the 80s and air temps in the 90s a drysuit is just an (uncomfortable!) complication.

 

[Cave Diver]

I'm with Ian on that one.

 

[Jax]

I'm going to disagree with the need for a drysuit. I've done maybe 20 dives to 200 feet (60m) in a ratty old 3mm wetsuit. If the watar temp is in the 80's its perfectly warm enough ( I'm a W.W.W.!) and the buoyancy swing is negligible.

At Tekweek in Cayman a couple of years ago people were doing 300 foot dives in shorts and T shirts.

With water in the 80s and air temps in the 90s a drysuit is just an (uncomfortable!) complication.

Maybe I missed it, but do you dive with dual bladders, Ian?