How can you determine if a boat is moving towards or away from you while underwater?

Determining whether a boat is moving towards or away from you while underwater can largely be assessed by changes in sound. Sound travels faster in water than in air, and it bends in different ways depending on temperature, salinity, and pressure. This means that as a boat approaches, the sound waves generated by the boat (such as engine noise or other sounds) become louder and higher in frequency. Conversely, as the boat moves away, the sounds diminish and may lower in frequency due to the Doppler effect. The changes in pitch and volume can provide clear indicators of the boat's movement relative to your position.

Other options, while they may provide some information, do not reliably indicate movement direction. For instance, observing bubbles may show a general vicinity but wouldn't directly indicate a boat's movement. The color of the boat is not relevant underwater, as visibility is limited, especially at greater depths. Waves created by the boat might give some information about its presence, but without additional context, waves alone do not clearly signal whether the boat is coming toward or moving away from a diver submerged underwater.