In what scenario might a vessel stop completely when hearing a horn?

Stopping completely when hearing a horn is a prudent action taken in situations involving potential collisions or navigational uncertainty. When a vessel hears a horn, it signals the presence of another vessel or indicates a navigational warning. If the crew is unsure of the other vessel's actions, stopping allows them to assess the situation fully, reducing the risk of collision. This decision prioritizes safety, providing time to evaluate the intentions of the other vessel and the surrounding environment before resuming navigation.

In contrast, other scenarios, such as being in clear water or approaching fixed navigation aids, do not inherently necessitate stopping upon hearing a horn. In clear water, the visibility of other vessels may allow for safer maneuvering. Approaching a fixed buoy typically involves known navigation practices that may not require an immediate stop, as the vessel's actions are often predictable. Traveling at maximum speed would generally be inappropriate if an uncertain situation arises, suggesting that the better practice would be to slow down or stop to avoid risks rather than continue at speed.