What Size BC Wing Should I Buy?

When diving, your wing needs only enough lift to compensate for the weight of your breathing gas plus the compression of your exposure suit at depth. Those using suits which don't compress much, such as dive skins or drysuits made of trilaminate or crushed neoprene, will also want some extra lift in order to be able to float comfortably on the surface. And of course the whole rig needs to float by itself if you doff it at the surface.

The wing is used to control buoyancy throughout the dive; a drysuit (if worn) should only be inflated enough to keep warm. At the beginning of the dive add enough gas to the wing to offset the weight of breathing gas in your tank; as you breathe the tank down, gradually vent small amounts of gas from the wing to stay neutral. At the end of the dive, when you are at 3 meters, if your tank is nearly empty there should be little or no gas left in the wing.

Buying more lift than you need offers no advantages and may cause other problems. Larger wings tend to cause more drag underwater and it can be more difficult to dump gas while ascending. Additionally, some divers with high capacity wings tend to overweight themselves and then try to compensate by adding a lot of gas to the wing; this makes buoyancy control difficult due to dynamic instability and creates a dangerous situation if the wing fails. Additionally some manufacturers which create large capacity wings put on bungie straps to keep these large wings from going all over the place.

Those who use integrated weights, such as the Halcyon ACB weights or various types of tank weights, may need a little extra lift. For example, if you have a single steel tank, steel back plate, canister light, argon system, and 7 kg of integrated weight then 16 kg lift is probably not enough to keep the rig from sinking if you doff it at the surface. The Halcyon single tank Pioneer wings have a unique expanding panel feature that allows the higher capacity models to have no more drag than the 12 kg lift model. Another solution is to just use a standard weight belt and avoid the problems associated with integrated weights.

Finally it should be noted that actual lift is not always equal to the rated lift. Often there are portions of the wing that are "pinched off" when a rig is fully assembled which will reduce its effective lift capacity. Therefore it is strongly recommended to either test a wing with your gear, or ask for references from people that have similar gear configurations before making a final decision.

Let's consider a few practical examples.

1. Single aluminum Luxfer S80 (11,1l), two-piece 6.5mm wet suit:
   The breathing gas weighs 2 kg or less, and the wet suit could lose up to 11 kg of lift due to compression if you go deep enough. So a 14 kg wing should be adequate. Note that the 14 kg should be sufficient to float the rig at the surface, unless there is significant weight worn integrated with the BP/harness.
2. Single aluminum Luxfer S80 (11,1l), tropical dive skin:
   The breathing gas weighs 2kg or less, and we would like another 4 kg for surface flotation, so any wing over 7 kg is enough. Note again that 7 kg should be sufficient unless there is significant integrated weight (which is unlikely with a dive skin).
3. Single low pressure steel 12 l, trilaminate drysuit:
   The breathing gas weighs 3 kg or less, we would like at least 4 kg for surface flotation (more for rough conditions), and drysuit divers often carry a little extra weight for warmth. Then we must consider that a steel 12l is at least -1 kg negative (some makes are more negative), a steel backplate is -3 kg and the canister light is usually at least -1 kg. A 12 kg wing might be sufficient for this configuration and some divers have successfully used a 12 kg with this configuration. However more divers opt for having a little more margin and choose the 16 kg wing, which should be more than sufficient for most applications. If significant amounts of integrated weights and/or non-ditchable weights are used a 20 kg wing may be more appropriate.
   
   
   Single wing 15 kg
4. Double low pressure steel 2x12 l, two aluminum S40 (5,7 l) stage tanks, trilaminate drysuit:
   The breathing gas could weigh up to 12 kg (although probably less due to using helium mixes). For the sort of dive where this equipment configuration would typically be used we want to be able to maintain neutral buoyancy without dropping any weights even if the drysuit completely floods (loses all of its lift). Most divers find that a wing in the 25 kg range works well.
   
   Wing Halcyon Explorer 55 (25 kg)

We don't need extra wing lift to bring up a heavy object from the bottom; this is dangerous since if you drop the object the extra gas in your wing will send you rocketing toward the surface. It is safer to use a lift bag instead.

Although it is possible to use a double tank wing with a single tank and adapter this can cause a lot of drag and gas trapping and is not a recommended practice. Always use the correct gear for the dive.