Here we go on the lift thing again....
A 100 lbs of lift is a bit much for doubles but then again 36 or even 50 is a little on the light side for many configurations.
At depth it is a moot point and a with proper weighting all you really need for lift in the BC is enough to overcome the addiitonal weight of the air in the tanks at the start of the dive and suit compression at depth. With a dry suit, suit compression is not an issue and a 20 lb bladder would be more than adequate.
At the surface though, there is more to it. People discredit the idea of considering what your gear weighs in air and for the most part I agree it is irrellevent. But you do need to consider how much lift is needed to get your head, shoulders, manifold, reg first stages, and the tops of your tanks out of the water. A dry suit with a tight neck seal may provide enough lift to augment a 36 lb bc, or maybe not, and it certainly won't be comfortable. It also presumes the drysuit is able to hold air. Similarly, in a wet suit, 36 lbs of lift will not be enough to get a cold water diver's chin above water. In either case you are going to have to ditch a lot of weight or deploy a lift bag to get comfortably bouyant on the surface.
There are few things less comfortable than just barely having your head out of the water with waves slapping you in the face and if you have to remain on the surface long, it can be very tiring. I think 60-75 lbs is a reasonable minimum amount of lift for many doubles configurations as it allows ample lift at the surface without having to rely on a drysuit for additional lift.
A 100 lbs of lift is a bit much for doubles but then again 36 or even 50 is a little on the light side for many configurations.
At depth it is a moot point and a with proper weighting all you really need for lift in the BC is enough to overcome the addiitonal weight of the air in the tanks at the start of the dive and suit compression at depth. With a dry suit, suit compression is not an issue and a 20 lb bladder would be more than adequate.
At the surface though, there is more to it. People discredit the idea of considering what your gear weighs in air and for the most part I agree it is irrellevent. But you do need to consider how much lift is needed to get your head, shoulders, manifold, reg first stages, and the tops of your tanks out of the water. A dry suit with a tight neck seal may provide enough lift to augment a 36 lb bc, or maybe not, and it certainly won't be comfortable. It also presumes the drysuit is able to hold air. Similarly, in a wet suit, 36 lbs of lift will not be enough to get a cold water diver's chin above water. In either case you are going to have to ditch a lot of weight or deploy a lift bag to get comfortably bouyant on the surface.
There are few things less comfortable than just barely having your head out of the water with waves slapping you in the face and if you have to remain on the surface long, it can be very tiring. I think 60-75 lbs is a reasonable minimum amount of lift for many doubles configurations as it allows ample lift at the surface without having to rely on a drysuit for additional lift.