How much lift do I need?

[parrothead600]

I am looking for a BCD for my daughter. She is approx 120# and dives with a 6.5mm 2pc. wetsuit and 22# of weight.(16# belt & 6# non-ditchable in pockets) alluminum 80 tank doing recreational diving, 130' and less.
Two of the BCD's that I am looking at are a Seaquest ADV & a Seaquest Spectrum2. The Spectrum2 is labled as 23# of lift. Will this be enough lift? I don't feel that there will be a problem @ the surface since the wetsuit will not be compressed, but I'm not sure if she will have enough control at the deeper depths.

 

[scubamickey]

That sounds like a lot of weight to me. I'm 120 lbs and I use that much weight when I dive with a dry suit and a thick undergarment. Has she done a bouyancy check?

 

[ththooft]

I'm not exactly sure of the left weight, but my wife dives about 18-20 lbs, is about 115 pounds, and very close to the same gear configuration. She should be totally fine with a traditional BC. My wife uses the ScubaPro Ladyhawk, and has not had any problems at all with lift even at depth. I've dove my Knighthawk with close to 30 lbs (first time I tried dry suit) and a shot of air was all I needed and I was fine.
Do you have a good LDS that you can talk to?

 

[scubamickey]

I dive with 8-10lbs when wearing a shorty. AL80 tank
12-14 lbs with a 3mm
15-18 lbs max with a 7mm

In saltwater and I'm 120lbs. I also have a Ladyhawk with 34lb of lift and that is way more lift than I need.

 

[spectrum]

If she is correctly weighted to be neutral at the end of the dive then she wil be about 5 pounds negative with an empty BC on the surface at the start of her dive.

So 23-5 = 18 pounds of lift compensation is available for additional loss in buoyancy. The only real loss will be from wetsuit (neoprene) compression. I suspect that style suit for that sized diver will be just about that buoyant and at worst case will loose 75% of it's lift. This would leave 4.5 pounds of extra to "get off the bottom",

I'd get her suit and all her other neoprene into a mesh bag and see what it takes to sink it. If it's more than 18 pounds I'd seek a little more lift.

She will begin gaining those 5 pounds of air weight in the form of lift as she breathes down the tank but she must be prepared to abort a deep dive early so keep that mass in the evaluation.

Pete

 

[scubatoys]

I've found for smaller girls that are diving cold, the back inflate BC's tend to work out better. The problem on the jacket styles are the amount of lift is determined by the size, XS will have less than a Small, Small less than a medium etc.. and actually in a scuba lab report last year, they showed most the manufacturers over rated their lift.

With back inflate, like a Zeagle Zena... you get your 35 lbs of lift whether you are in an XS or a large.

If she is wearing 22 lbs of weight, on a bc that might be over rated at 23 lbs of lift... you may find she takes it off in the water, and away it goes... sinking to the bottom.