Talk me *OUT* of a BP/W setup

[Shotmaster]

LOL

 

[stuartv]

I dive double 120s and an AL40. Where am I going wrong?

I figure:

18# for gas in the 120s
3# for gas in the AL40

I carry enough lead to make sure that if shtuff happens and I end up OOA on back gas and breathing my deco bottle down to empty while hanging at 10' or whatever, that I can hold that depth without corking to the surface.

If I want to keep my head out of the water at the start of the dive, I need 21#, plus about 6# for the weight of my head out of water, plus however much buoyancy I could lose if my dry suit neck seal pops off and I lose all the air on the inside.

So, I get in, descend, and my neck seal pops off immediately, I need 27# of lift plus however much buoyancy I just lost from my suit in order to get neutral. My dry suit gives me more than 11 # of lift when I'm wearing cold water undergarments. So, if that happened to me and I only had a 38# wing, I would probably have to drop my deco bottle and also be wearing a weight belt that I could drop, in order to get back to the surface and keep myself afloat with my head out of water. Am I missing something?

Personally, I would rather have a little bit more lift capacity and know that I won't have to drop any of my gear. With lead running $5/lb, I don't even want to drop that if a little more wing capacity would prevent the need.

I determined that, for me, a 45# wing is the smallest I would dive with with my double 120s and an AL40. But, if I have missed something, I would appreciate it if someone would break it down for me.

My AN/DP instructor told me a 45# was the minimum he would accept and he recommended a 60# wing on the basis of future training plans avoiding having to buy a second doubles wing later.

 

[cool_hardware52]

A 38# wing for diving doubles? How did you determine that that will be enough lift for diving doubles on deco dives?

We offer as a standard Item a 38 lbs doubles wing. We also have produced limited runs of 32 lbs and 25 lbs doubles wings, but you have to convince me that 1) You are teachable, 2) Not an "knobhead" (to borrow a colorful British-ism) before I sell these special order items.....

Tobin

 

[Shotmaster]

My Classic has 58.5 lbs of lift and is rated for 100 cuft steel doubles. If you max out a smaller BC/wing you have no reserve if things get sticky Underwater or on the surface. Better have strong legs so you can kick it to the surface. I prefer to plan for the worst, just in case. There is an old saying about air plane pilots "there are bold pilots, and there old pilots, but there aren't many old bold pilots".

 

[JohnnyC]

25lb doubles wing/. I bet that would go great with a little set of LP50 doubles for NDL diving.

 

[cool_hardware52]

My Classic has 58.5 lbs of lift and is rated for 100 cuft steel doubles. If you max out a smaller BC/wing you have no reserve if things get sticky Underwater or on the surface. Better have strong legs so you can kick it to the surface. I prefer to plan for the worst, just in case. There is an old saying about air plane pilots "there are bold pilots, and there old pilots, but there aren't many old bold pilots".

The single most important factor in determining required lift is the buoyancy of the exposure suit. The volume of the back gas plays some part, but I shake my head when I see wings sold as being "rated" for XX tanks, and there is zero discussion of the suit buoyancy.

BC's or Buoyancy Compensators are needed to compensate for things that lose buoyancy (become less positive) WRT to depth. Only the diver's exposure suit loses buoyancy. Cylinders don't lose buoyancy, in fact they become less negative / more positive as the gas is drained.

Tobin

 

[cool_hardware52]

25lb doubles wing/. I bet that would go great with a little set of LP50 doubles for NDL diving.

Bingo! (except mine are 2x LP 45's)

Tobin

 

[dberry]

A 38# wing for diving doubles? How did you determine that that will be enough lift for diving doubles on deco dives?

My instructor said so. He said he personally doesn't like anything bigger than 40#, and specifically said 38# would be fine for the pair of LP85s I'd be training with. I'm clueless, of course, but the instructor seems to have a bit of experience in these matters. I'll guess I'll find out on July 5th when I meet him for the start of the 5-day combo course.

The course is being taught by John Chatterton in Pompano Beach; based on some recommendations I decided it was worth the trip to Florida.

 

[stuartv]

The course is being taught by John Chatterton in Pompano Beach; based on some recommendations I decided it was worth the trip to Florida.

Interesting. He should certainly know. I know several people who have trained with him and was considering going down there to do Trimix. I will look forward to hearing how your class goes. I hope you'll post a report.

 

[doctormike]

The course is being taught by John Chatterton in Pompano Beach; based on some recommendations I decided it was worth the trip to Florida.

It definitely is!