What is the signal audibility range for vessels less than 20 meters?

The audibility range for vessels less than 20 meters is specifically important in the context of maritime safety and communication. The correct choice reflects the established parameters for sound signals that smaller vessels should be able to produce and recognize for effective communication and signaling during distress situations.

In this case, the range of 180-450 Hz is significant because it encompasses the low-frequency sound signals that can be more easily detected by the human ear, especially under conditions where visibility is limited. This range is defined by guidelines which ensure that smaller vessels can effectively communicate their presence and state to other nearby vessels or rescuers.

The options that suggest ranges beyond this specified limit do not align with established maritime protocols, which are based on extensive research into sound propagation in marine environments and hearing sensitivity. Keeping the range limited helps in focusing on the intelligibility and reliability of the distress signals emitted by vessels of this size in various maritime scenarios.