How often should sound signals be used in restricted visibility?

The correct choice is that sound signals should be used at least once every two minutes in restricted visibility. This guideline is established within the COLREGs rules to ensure navigational safety when visibility is compromised, as in fog or heavy rain. The use of sound signals serves as a means of communication between vessels, helping to indicate their presence and intentions to nearby vessels that may not be able to see them.

By mandating a sound signal at least every two minutes, the COLREGs provide a structured approach to mitigating the risks associated with restricted visibility. This frequency strikes a balance; it assures that vessels can maintain awareness of each other's location without overwhelming the soundscape with constant signals.

In contrast, using sound signals every minute might lead to confusion and clutter in the immediate marine environment, potentially masking important signals from other vessels. Waiting as long as five minutes or only using signals when deemed necessary may not sufficiently alert other vessels to your presence, increasing the risk of collisions. Thus, the prescribed interval helps promote safety on the water by ensuring that vessels remain alert to one another in conditions where visual contact is limited.