Genesis, I never said *anything* about ditching at depth.
You just didn't realize it.
You are making the mistaken assumption that you lose all the buoyancy of your suit in the event of a catastrophic flood.
If your undergarment doesn't retain at least a good deal of its buoyancy characteristics even when soaked through, then you are diving the wrong undergarment (try throwing your thinsulate undergarment in the bathtub sometime and see if you can get it to sink).
I've tried it. Undergarmets made out of thinsulate or polartec have only a couple of pounds of buoyancy when sopping wet. I can send mine directly to the bottom with a 2lb lead softweight sack, and I suspect that a 1lb would be enough (I don't happen to have one, so I can't verify that.)
2lbs is about 10% of the total positive buoyancy that my suit miparts when it is being worn. That is
insignificant to the computation and as such it is safe to ignore it.
Virtually
all of the buoyancy from a shell drysuit is from the
air trapped in the fibers of the undergarmet and the suit's "free air space" itself. Dove correctly, the "free air space" is at a minimum, but its still a huge component of the total - probably 75% of it. The trapped airspace (in the undergarmet) will be rapidly replaced by water (with the air venting to the water around you) if the suit has a catastrophic flood.
As I stated, the only lift needed is the lift needed to float the rig on the surface.
You will float, even in a totally flooded suit.
No you won't. I intentionally flooded mine in my pool (with the chlorine at a VERY low level!) when I got it and was teaching myself how to dive it (by sticking my finger down the neck seal until it was COMPLETELY full, taking care to let ALL the air out.)
I estimate that it had less than two lbs of buoyancy left at that point, and that is probably the intrinsic buoyancy of the neoprene booties and material the suit is made of.
If the suit experiences a catastrophic failure (say, its ripped open by the edge of a wreck) you will find that it has virtually
zero buoyancy. It won't be quite zero, but it will be damn close to it.
Second, ANY PART of the suit that is above water when you surface will attempt to make you sink to the surface. This is because for every gallon of water above the waterline of the suit, it exerts -8lbs of buoyancy (the weight of the water in air.) Therefore, in the event of a catastrophic flood you have two problems - the first is the near-total loss of buoyancy of the suit, and the second is the extreme difficulty in keeping any part of your body in that suit out of the water - like your mouth, for example, which is damn close to the top of the suit (and thus the "natural" top when flooded.)
Now if you are diving a NEOPRENE drysuit then this does not apply, as the neoprene is naturally buoyant. Even "crushed neoprene" has inherent buoyancy. But for a shell suit, which is what I dive, it
absolutely is true; I've tested it personally.
If needed, ditch the weights on the surface to make yourself more comfortable.
There is no need to have anything over 36# of lift in a singles rig, and failing someone carrying a truly excessive amount of lead, 27# is more than adequate.
Horsefeathers.
I've already shown why 27lbs is marginal for many dry suit diving configurations (including my own.) 36 is adequate, but just barely.
The argument for NOT having more has traditionally been one of the penalty paid in the form of increased drag (due to bulk) for doing so.
That penalty argument no longer applies with the Oxycheq 45; its profile is
identical to the 30; in fact, they will sit exactly on top of one another without any overhang. The "expanding" part is on the INSIDE, near the TANK, and as such you pay no penalty for it unless you're USING it (at which point you're on the surface and the slight additional drag is irrelavent anyway.)
