How to determine ideal buoyancy lift on a BC?

[Scotttyd]

I am recently certified (6 dives under my belt!!!!!). I am looking at buying a BC, how do I determine what my ideal buoyancy lift is?? Is it better to have a higher or lower Buoyancy lift?

 

[tedwhiteva]

The buoyancy lift is determined by the amount of equipment you wear - typically the type/number of tanks. If you will be diving AL 80s, a 30 lb lift BC or backplate/wing is adequate. You don't needhte bigger lift until you go with large/double tanks

 

[Doc]

Is it better to have a higher or lower Buoyancy lift?

It is better to have a lift capacity higher than the weight of the gear that you will be wearing. If the capacity is lower than you will need, we'll re-start this discussion at accidents and incidents forum.

Most of us are positively buoyant, certainly in sea water. With the addition of lead weights, we only take on as much as needed to make ourselves approximately neutral- at the "end" of the dive when our tanks are lighter.

You really don't need lot of lift capacity for recreational divng.

 

[Rainer]

Search is your friend. Find any of 100s of posts where Tobin (cool_hardware52) answers this question.

 

[Thalassamania]

Do you dive wet or dry and what sort of tank arrangement do you favor? Until you're at a point in your diving where you can asnwer those two questions it's kind of hard to come up with a good answer.

 

[Charlie99]

It is better to have a lift capacity higher than the weight of the gear that you will be wearing.

Just to clarify, the lift needs to be greater than the negative buoyancy at depth. Many like to add another 10 pounds or so of extra lift beyond that. To say that you need more lift than the equipment weight makes no more sense than saying that you need lift greater than your body weight.

There are two basic requirements ----
achieve positive buoyancy at depth (wetsuit compressed) with full tanks
and
float the gear on the surface if you need to degear for some reason.

 

[Rainer]

Just to clarify, the lift needs to be greater than the negative buoyancy at depth. Many like to add another 10 pounds or so of extra lift beyond that. To say that you need more lift than the equipment weight makes no more sense than saying that you need lift greater than your body weight.

There are two basic requirements ----
achieve positive buoyancy at depth (wetsuit compressed) with full tanks
and
float the gear on the surface if you need to degear for some reason.

Exactly. Float the rig at the surface (with you out of it) and keep you and the gear neutral at max depth.

 

[Davidstealey3]

i like the anwsers here. you need to figure out what the mosgt weight will be that you will wear at one time and make sure there is enough lift to get you postively buoyant. some BC's are made for warm water and dont have as much lift as some of the others. zeagle for instant has bc's with i think 24 & 32 pounds of lift. good luck with your search.

 

[markfm]

My "warm water" Reefrider has 32 lb lift. For me that's actually plenty, even in my drysuit.

An AL80, full, is about -2 lb. My net weighting in a drysuit is 18 - 20 lb. That means that even with a "lightweight" BCD, I have a reserve, even on a full tank.

I also have a Zone II, 60 lb lift. The extra lift isn't really necessary for me, but it's built really solid, could take a pounding (the Reefrider has several hundred dives, still in super shape, so is clearly well made).

Really massive lift BCDs beat the heck out of me, unless someone is doing specialized things. They're just plain large (don't pack as well for travel), can be a pain to use (have to be careful to not put too much air in, or you'll face plant -- this can happen in any back inflate unit, but the higher the lift the easier it is to do this).

 

[TSandM]

I'm surprised Tobin hasn't chimed in here (maybe he's out diving ).

Basically, your BC, as somebody has said already, has to do two things: One is float you and your gear at the surface, and the other is to compensate for the loss of buoyancy of your exposure protection with depth.

The combination of diver and exposure protection, in any cool or cold water circumstance, is likely to be positive because of the intrinsic buoyancy of insulation. We therefore wear weight to bring the diver/gear system to neutral. The weight can be worn on the diver, or on the equipment. In very cold water diving, the required weight can be substantial. Therefore, if you are cold water diving with weight integration, you may need a good-sized flotation bladder to keep your gear on the surface when you are not wearing it. For example, a 100 cf steel tank, full, will be at least 7 lbs negative. Add 20 lbs of lead in weight integration, and you are very close to the lift capacity of a 30 lb BC, and you haven't figured in the weight of your regulator or any negative accessories you may be carrying. 30 lbs of lift is probably inadequate for that rig.

If you are wearing a thick wetsuit, you could lose 20 lbs or more of buoyancy at maximum depth. Your BC needs to compensate for that, because you had to wear weight to sink that much buoyant material -- So when the buoyancy from the neoprene disappears, you're that much "overweighted".

So, as Tobin always eloquently puts it, you should measure the negative buoyancy of your gear without you in it, and also determine the positive buoyancy of your exposure protection. (You can do this with a wetsuit by throwing it in a tub and seeing how much weight you have to pile on it to make it sink. For a drysuit, you really have to get into the water and hold weights until you see what makes you neutral.) Whichever number is greater determines the lift you require.