What is the primary function of a buoyancy control device (BCD)?

The primary function of a buoyancy control device (BCD) is to assist divers in controlling their ascent and descent. This is essential for safe and effective diving, as it allows divers to adjust their buoyancy while underwater by adding or removing air from the BCD. By inflating the BCD, a diver can become more buoyant, which helps them ascend. Conversely, deflating the BCD allows the diver to descend by reducing their buoyancy.

This ability to manage buoyancy is crucial for maintaining neutral buoyancy, which is when a diver neither sinks nor floats but remains suspended in the water. This state enables divers to conserve energy, explore underwater environments effectively, and prevent rapid ascents or descents that could lead to potential hazards such as decompression sickness.

In terms of the other choices, while carrying extra weight can be a strategy for stability and descending, it is not the primary purpose of a BCD. Insulation against cold water is typically the function of wetsuits or drysuits rather than BCDs. Increasing swim speed is not directly related to the function of a BCD either; the BCD's role is more about buoyancy management than propulsion through the water.