BC's (Bouyancy Compensator)

WHEN the adjustable buoyancy life-jacket (ABLJ) was invented, it revolutionised diving because it meant that a diver could be as neutrally buoyant as a fish. It acted just like a swim-bladder.

Stab-jacket or waistcoat-style BCs improved diving even further because they hugged the diver's body better. Shoulder straps and buckles were added to form today's conventional BC.

Some BCs, such as the Buddy Commando and Zeagle Tech Diver, are suitable for use with drysuits and twinsets. Others, like the SeaQuest Dimension XP, are intended for travelling divers who might not even wear a wetsuit. Some have a small 400ml auxiliary air cylinder built in as an independent means of inflation (for example the Seapeks, Buddy and Hydrotech Seaform 400). If you prefer a BC that lays you firmly on your back at the surface, waistcoat-style jackets like the Mares Vector High Lift and Scubapro Classic could be the answer. If you want to integrate your weights, BCs like the Oceanic Chute 1 and SeaQuest Quickdraw may be ideal.

Whatever BC you choose, make sure it offers enough total buoyancy at the surface, and do not be misled by a manufacturer's maximum lift figures (these do not take into account parts of the jacket that remain out of the water at the surface). You also need to consider a jacket's buoyancy underwater, plus features like pockets and D-rings, and make sure the jacket will not encumber you with too much bulk while swimming.

It is essential that a jacket fits you properly. Remember that the gravitational forces at work when you try on a BC in the dive shop are entirely different from the upwardly buoyant forces at work under water.