The Buoyancy Control Device (BCD) (also know as Buoyancy Compensator – BC) is one of the most critical pieces of equipment and needs serious attention when a diver decides to buy one. If you think about it the BCD is like a central structure that some heavy equipment is supported from or is fixed to. A poorly fitting BCD is a real no-no and can ruin your experience of a dive.
What is a BCD? In it's simplest form a BCD has three functions:
- Provide a means to control buoyancy
- Provide a means of securing a cylinder
- Provide a means of securing the whole thing to the diver.
Unfortunately we have not developed the ability to survive underwater without the use of equipment. One of our failings is that we have a tendency to sink uncontrollably when a big steel cylinder is attached to our back. As a result divers need an inflatable bladder that gives us control over our buoyancy, allowing us to achieve that all important neutrally buoyancy. As with everything the BCD has been slowly developed and built upon over the years, going from the purest device to the advanced systems that we have now. The principle is the same but they just need to be able to support more additions including integrated weight systems, easy adjustment and quick releases, comfort and padding, more attachment points for accessories, etc. With all this potential equipment attaching to a BCD you can quickly see why it needs to be secure, suitable for the diving you'll be doing and a good fit. Types Ignoring the intended use and weight for the moment, 99% of BCDs fall into one of two categories, traditional or back lift.
A traditional style of BCD is the most commonly used type and features a harness system with a wraparound buoyancy bladder through which air is free to migrate. The harness will typically feature adjustment quick release clips across the front and on the shoulder straps. This style of BCD provides much more stability whilst on the surface thanks to air being forced to the front of the BCD, giving the diver 'head up' support.
Back lift BCDs are much less common amongst recreational divers. All the buoyancy is housed within a rear bladder that usually features some sort of elastic or bungee system to retract the bladder back in on itself when deflated. The harness tends to be more open, giving divers better freedom of movement as there is no side bladder to restrict space and movement. A back lift BCD will usually allow for better horizontal trim whilst diving but do have a tendency to tilt divers forward whilst of the surface until the diver develops a compensating technique. The remaining 1% are hybrids, a combination of both traditional and back lift to help eliminate some of the short comings of both systems. Hybrid BCDs will usually include features like expanding rear bladder sections or modified harness systems.