How much BC lift do I require?

[leadweight]

weights get ditched, especially the injured diver's weights.

 

[Gdiver]

I have been looking on ebay for a starter BC. After I find one I may be interested in, I do some research. Thus far, the term LIFT CAPACITY has been confusing. :wacko: Can someone please explain? Thanks

 

[DA Aquamaster]

BC's differ in the amount of lift that they can provide. A BC made for warm water travel diving may only have 18-20 pounds of lift which makes it inadequate for cold water diving where more weight needs to be carried to accomodate a 7mm wetsuit.

A BC with inadequate lift will not be able to support you high enough on the surface and may not provide enough lift on the bottom to maintain neutral bouyancy. Most BC's provide somewhere between 30 and 45 lbs of lift. The BC you use needs to be provide enough lift to able to keep your head well out of the water on the surface with all your equipment on and with a full tank.

There are also back floatation BC's and backplate, harness and wing assemblies that are designed for technical diving that will provide upwards of 75 lbs of lift which can be useful when using double tanks and stage bottles. Redundant air bladders and inflators are also an option in this class.

Many backplate and harness assemblies can accomodate wings of varying sizes making them adaptable to warm water travel diving, single tank cold water diving or technical diving.

You need enough lift to meet your needs but more is not always better. To much volume and lift capacity can make it easier for an inexperienced diver to get into trouble with an out of control ascent.

 

[Gdiver]

Thanks for the great info! That's exactly what I was looking for.

 

[IzzyTahil]

Does anyone know if there is some kind of table or reference that shows the max weight load against the lift capacity of a wing? For example, whats the max weight a 45lb or 55lb bladder can handle?

 

[jamiei]

well, most 45lb wings for instance don't necessarily have 45 lbs of lift... for whatever reason... other than that I have to say... what??? can handle or lift?

 

[scubasean]

I've always thought that the 45 or 55 was the weight the bladder could support in water. So, if you had a B/C, integ. weights, and tank, etc. weighing that amount, and took it off in the water, a full bladder rated for that amount or greater would float it....

I could be wrong...

--Sean

 

[DIR Tec Diver]

It all depends on the tanks you will be using, and their buoyancy in the water both full and empty. That will determine the wing size you need. If you don't know the tanks or you will be renting from shops thus getting a lot of different tanks, base it upon the largest size you will be using as to ensure that you don't get into an uncomfortable situation in the water, however if you know that for example you will be using an aluminum 80 all the time, get a small wing with about 27lbs of lift. More than that will only cause drag, resistance and inconsistent buoyancy and trim.

It is so true that the lift capacities don't usually match up, and the specs put out by the tank manufacturers are even less accurate, so unfortunately you will have to look at each bc and tank individually.

 

[Charlie99]

DIR Tec Diver once bubbled...
It is so true that the lift capacities don't usually match up, and the specs put out by the tank manufacturers are even less accurate, so unfortunately you will have to look at each bc and tank individually.

Reputable manufacturers deliver the lift they specify. If they have the CE label, it has to be within a specified tolerance, IIRC, 10%.

It's easy to test your BC. Just weigh it. Fill the bladder with water, then weigh it again. A true purist would then add 2.5% for fresh to salt adjustment. Or just count how many pints or liters it takes to fill the bladder. My Seaquest was within a pound of its 34# spec.
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This is a LIFT or buoyancy spec. You can dive with hundreds of pounds of equipment, as long as it is close to neutral buoyancy.

 

[Doppler]

IzzyTahil once bubbled...
Does anyone know if there is some kind of table or reference that shows the max weight load against the lift capacity of a wing? For example, whats the max weight a 45lb or 55lb bladder can handle?

What you have to do is find out the in-water weight of the equipment you dive with. Knowing what it weighs on land will not help.

Specs for tanks (full) are available on line. Be aware that most do include valves. You could do the calculations for every peice of equipment working out its displacement and therefore it buoyancy characteristics.

An easy way is to get your hands on a fishing scale... and go to your local pool. assemble your gear -- BPWings, Full Tanks, etc. and put them into the water. Weigh them. Write that figure down. Now get into the water wearing your thermal protection. How much weight do you have to hold to float with your nose/eyes above water? This is Your buoyancy factor... your lift if you like. Take it off the apparant weight of your gear. The remainder is the lift you need... depending on the tanks, you may find that you need to add lead (weight belt, V weight) to sink, or you may find you are a few kilos negative. This figure will characterise which size wing is good for you to use.

Generally speaking, steel doubles, dry suit, couple of aluminum stages and light, regs, etc. are more than covered by a #55 wing.

For the record, I dive with a dry suit and 400 thermal protection, three stages, 104 steel tanks, a small light (Helios) a video camera, and all the regular support equipment, and find #55 is more than enough.

Two points, most divers dive over weighted. You likely fall into that category.