ScubaTwo:
I dont suppose anyone will see this reply as the thread is over 2 years old but here goes anyway. I did a search on "lift capacity" and have been reading the threads all morning. When I found this thread I was very excited as the original poster asked the exact question I was looking for. I was so dissapointed that all he was told was to do a search since that is how I got to this point to begin with. I did find many threads with a link to calculate lift capacity but the links were no longer working. So if anyone sees this post and can tell me a simple way (Im terrrible with numbers ) to calculate how much lift capacity a person would need I would be very grateful.
Thank you.
There are two main factors that contribute to determining an optimal lift capacity for a BC: (1) the BC has to be able to keep the entire rig on the surface and (2) the BC has to compensate for any changes in buoyancy during the dive.
The capacity required for (1) is easy to calculate, if one knows the negative buoyancy of the full tank(s). This is rarely an issue. The calculation for (2) involves two factors: the reduction in buoyancy of the tank(s) during the dive, and changes in buoyancy associated with compression of the exposure suit. And of course, one should add a safety factor.
Maybe someone else will put precise numbers on these factors. As a rule of thumb, larger lift capacities (>40 lbs) are required when using thick exposure suits, and large capacity, multiple steel tanks (doubles, stage bottles etc), which is usually associated with cold water / tech diving. Single aluminum tanks, tropical wet suits, or dry suits (because their buoyancy remains more or less constant) reduce the need for lift.
Diving a single 15l steel tank, I am OK with a 26 lb lift wing when diving dry. When diving wet, I need at least 35 lb. In tropical waters, wearing swimming trunks and a T-shirt and carrying an Al80, I can do without a BC
HTH.
