Buoyancy Compensation Device
Jacket type BC on diving cylinder
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| Acronym | BC or BCD |
|---|---|
| Other names | Buoyancy control device |
| Uses | To adjust and control the overall buoyancy of the diver |
| Related items | Backplate and wing |
A buoyancy compensator also called a buoyancy control device, BC, BCD, stabilizer, stabilisor, stab jacket, wing or ABLJ depending on design, is a piece of diving equipment containing an inflatable bladder which is worn by divers to establish neutral buoyancy underwater and positive buoyancy on the surface, when needed. The buoyancy is controlled by adjusting the volume of air in the bladder. The bladder is filled with gas from the diver's air tank via a low-pressure hose from the regulator first stage, directly from a small cylinder dedicated to this purpose, or from the diver's mouth through the oral inflation valve.
All BCs will have some features in common:
In addition some BCs may include other features:
There are three main types of BC based on buoyancy distribution:
An adjustable buoyancy life jacket (ABLJ) is fitted around the neck and over the chest, secured by straps around the waist and usually between the legs. They are sometimes referred to as "horse collars" because of their resemblance, and are historically derived from the inflatable UDT vest or Mae West life jacket issued to World War II flyers and divers.
They were developed in the 1960s and have been largely superseded by wing and vest type BCs, primarily because of their tendency to shift the diver's center of buoyancy towards the head with inflation, which adversely affects the diver's trim underwater. The ABLJ's location on the diver's chest and round the neck provides the best buoyancy distribution of the buoyancy compensater designs when it comes to floating a distressed, fatigued or unconscious diver face-up on the surface in the event of a problem.
The Dacor Seachute BC4 had unique upper and lower bladders. The upper bladder was around the neck and could be inflated by the CO2 cartridge for use as a surface life jacket. The lower bladder was over the diver's stomach area, and was inflated by LP gas from the regulator, for buoyancy control underwater. This arrangement provided better buoyancy distribution for trim control while diving than most other front inflation systems.
Vest BC, stab jacket, stabiliser jacket, stab, waistcoat or disparagingly "Poodle Vest" BCs are inflatable vests worn by the diver around the upper torso, which incorporate the cylinder harness. The air bladder may extend from the back around the diver's sides ("wraparound") or may only cover the back ("back inflation.")
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Wikipedia