Understanding Scuba BCD Types and Buoyancy Systems I've been diving since the late '70s, and I can tell you that understanding scuba BCD types explained properly will save you money, frustration, and potentially your safety underwater. The buoyancy compensator device is the single piece of gear that separates confident divers from those who flail around burning through their air in twenty minutes. After watching thousands of divers over four decades, I've learned that most people don't understand what they're buying until they're already fifty dives deep with the wrong equipment for their diving style. What Is a Scuba BCD? A BCD—buoyancy compensator device, or buoyancy control device depending on who you ask—is an inflatable bladder system that lets you control your position in the water column. Think of it as your adjustable life jacket, exce ...