How much lift does one need

[mainediver8169]

By definition alone I can see you need a certain amount of lift to keep yourself afloat. My question is how do you know if you have enough. For instance, say a large bc by a certain company has 34lbs of lift, you wear a large how do you know this is enough lift? Is their a formula? I am just a rec. diver very newbie, and am getting my gear but want to make sure what I buy is going to work safely and efficently for me. I dive in water 50-60 degrees at home and then whatever the water temp is on dive trips. Guess what I am getting at is, if I am diving with a 7mm suit, 20lbs weight, tank and maybe a light will something like that be sufficent?

Also, would like to know how to figure it out so its safe.

Thanks

 

[herman]

You need enough lift to do 2 things. Keep your gear afloat when you are not in it with it fully equipped, which includes weight if it is weight intergreated. And you need enough lift to compensate for wetsuit compression at depth. This will never be more than the amount of lead you need to become neutral at the surface. Choose your lift requirements based on the larger of these 2. In the case above assuming a weight intergrated BC, 34 lbs should do nicely unless you are using large steel tanks. Without weight intergration, a 20 lb wing would be fine again assuming you are not diving large steel or double tanks. Most divers have way more lift than they need. If you start tech diving, all of the above goes out the window, that is a totally different discussion.

 

[Michael Kazma]

If diving a single tank 34lbs is good. Once you go into doubles then you need a 55lb wing.

 

[Dyno Bill]

If diving a single tank 34lbs is good. Once you go into doubles then you need a 55lb wing.

The old Dacor Rig I have used for years has a single bladder or wing for the lack of a better description that has a lift capacity of 75 lbs and it is made to use 2 wings equaling 150 lbs lift. I use a small amount of air so it's only been blown up a couple of times to help bringing something to the surface. I know thats not considered a good practice but sometimes things need to be done to achieve something else. I was at Veterans Park yesterday goofing off with the wife and we watched a number of divers come and go and to my amazement I didn't see one bp/w setup while we were there. They were all rear flotation bc style rigs. I did chat with a DM that was goofing around as well and he said he used a bp/w in favor of a rear flotation bc that lived in his closet.

 

[JBRES1]

When I dove a BC, I too had a large bc, and a 7mm farmer john wet suit.
I am 5'11" and 210 lbs.
I dove with 24# of lead using an al80 , and 20#s when I went to a steel 100.
I had 32# of lift, and the lift was more than enough to float my gear without me, and with me in it.


Hope this helps,
Jim breslin

 

[GrumpyOldGuy]

Herman pretty much nailed the answer on the first reply.

The extra lift on most jackets provides a lot of tolerance for grossly over-weighted divers and can lift their face out of the water further than the more modest sized BCD. Of course you pay for this in a bit larger size and more drag. I prefer the smaller 30lb range of lift and I weight in at 220/XL in an 8M FJ+J with 30lbs lift. It is just the right size for me.

 

[captndale]

The minimum lift you need is:

The amount of lift you need to remain comfortable at the surface (About 10 to 11 lbs.)
Plus
The weight of the gas in your tanks (6 lbs. for an Al 80 filled with air.)
Plus
The compression of your wetsuit.
Plus
The compression of any other compressible components of your dive gear (Padding, etc.)
Plus
The amount by which you are overweighted.

 

[Indian Valley Scuba]

Remember, BC lift capacity, like many other things in life, is best calculated taken the words of architect Ludwig Mies van der Rohe to heart - "less is more".

Start small and only add what you absolutely can prove you need - you will be better off for it.

 

[elmer fudd]

There are two standard rules of thumb regarding lift.

1) You need enough lift to make your BC/tank buoyant. You wouldn't want to take it off at the surface, before you climb into a boat, only to watch your fully inflated rig sink to the bottom.

2) It ought to provide enough lift to make you buoyant when everything else is providing minimum lift. So if you're at 132' and your wetsuit is compressed and only producing 1/5 the buoyancy it did at the surface, your BC needs to be able to compensate for that and for whatever extra weight you are wearing and for the extra weight that a full tank of air has vs. an empty one.
If you are wearing a drysuit, your BC should provide enough lift to make you buoyant in the event of a total flood.

For most of us diving single tanks 30 lbs is enough, although you can get by with less in warm water.

Personally, however, I wouldn't regard either one as being set in stone. There are ways to compensate. If your rig sinks, you can hand off weights to the boat prior to boarding, or clip your rig to a secure line. People dove for decades from boats with negative rigs. Likewise, if you have a total flood at depth you can plan on dumping some of your weight. Just make sure it's not all in one massive package, like with a 30 lb. weight belt. With my drysuit, I wear 12 lbs. in pouches on each side.

 

[on_two_wheels]

You're in Maine so if you're diving locally I'm guessing it won't be long before you're diving dry (if not already). Keep in mind, the comments about compensating for a wetsuit don't apply to a drysuit. I use a 30 lb wing with the following:

8 lbs of lead
6 lb steel plate
6 lb STA (single tank adapter)
steel tank, 95 or 120. (either -1.7 or -7 at 500 psi respectively)

Its' enough to float my rig without much excess. Even if I had a fully flooded drysuit, I can make it to the surface, that being the only situation that I'd be solely dependent on the wing. You've learned the importance of redundancy and you're in the northeast....learn drysuit diving and you'll be glad ya did. Then your BCD only needs to float your rig, really.