Al plate for cold water - is crushing number worth it ?

[stargost]

A lot of this is somehow theory, stolen from a few posts, especially Tobin, that's why i post here...
But before likely getting a double rig, I’d like to have a few more feedback on how much attention to theory needs to be paid, leading eventually to the choice of the plate.

Starting: I’m diving cold SoCal ;-), planning doubles HP100, and drysuit has buoyancy of +25.

So if I do the math right:
-------------------------
2xRegs+manifold+SS plate+tank strap+can light+2xHP100 empty =~ - (2*2+2+6+3+2+2*3) = -23lbs

- To get neutral at end of the dive => need only 2pounds of additional lead
- To get the all rig to float by itself at the beginning of the dive => need ~ -23(above)-2(lead)-2*6(air) ~> 37lbs lift wing -> theory says I can get the HOG38 double wing but this is rather at the limit and a 40lbs evolve wing should be better …. (I'm kidding, DSS 42 torus has to be the solution here )

- Now, here is more theory and bad luck: assuming both suit and wing fail at depth, I’m supposed to bring the all rig back up. If the suit buoyancy is 25 when dry, and let’s say it fails bad and get flooded completely, its buoyancy may get reduced a bit (right ??). Let’s assume to +20. This means I need to swim up about -17lbs or -15lbs up if I ditch the 2lbs of lead. It is still a lot, probably too much from 80-100ft.

- So here is my question: wouldn’t it be better to get an AL plate, and add more on ditch able weights? With AL plate and 7lbs in lead, this gets the Delta(rig+suit) to -10lbs to swim up, and probably the +20 for the suit being flooded is conservative.
- The drawback of this would be on trim as you get more lead at waist rather than on the back / plate.

Any comments ? Is theory worth it or I just create a problem where there is none ;-) ? I don’t see many (any) people diving with AL plate around here, so there could clearly be some good reason. Still…

 

[cool_hardware52]

Starting: I’m diving cold SoCal ;-), planning doubles HP100, and drysuit has buoyancy of +25.

Worthington HP100 are -2.5 each.

With a light weight plate (al or Kydex) your rig will be about -32 lbs with full bottles and will provide about 16 lbs of ballast with empty tanks.

You will need another ~10-12 lbs of ballast somewhere.

If you use a SS plate your rig will be about -36 with full cylinders and it will provide about 20 lbs of ballast with empty tanks. That still leaves 4-6 lbs on a belt or in soft weight pouches between the wing and plate. If you put your ballast on your rig it will be about -42 lbs with full tanks.

I'd recommend a Torus 49 wing as it is shaped to provide more lift near the divers shoulders, this is often helpful for new doubles divers. A little "extra" lift may be handy if you choose to add more undies in the future.

Plate material? You can probably use either a lightweight plate or a SS plate. In short if you have a plate use it, if you do not I'd recommend an SS plate.

- Now, here is more theory and bad luck: assuming both suit and wing fail at depth, I’m supposed to bring the all rig back up.

That's two failures, not too likely and is exactly why you want to develop a good team.

Tobin