When might a vessel need to use sound signals instead of visual signals?

A vessel needs to use sound signals instead of visual signals primarily in poor visibility conditions, such as fog or heavy rain. This is because visibility is significantly reduced in these situations, making it challenging for vessels to see visual signals from other vessels or navigational aids. Sound signals serve as an effective alternative, allowing vessels to communicate their presence and intentions to others nearby despite the obscured visual range.

Using sound signals ensures that vessels can still navigate safely and avoid collisions when visibility conditions are compromised. While visual signals are effective in clear conditions, they lose their utility when mariners cannot see them. Thus, understanding the specific scenarios that warrant the use of sound signals is crucial for maintaining safety on the water.