When must the stand-on vessel use sound signals?

The stand-on vessel must use sound signals when she alters her course if the give-way vessel is not altering hers because this action communicates her intentions to other vessels nearby. According to the COLREGs, the stand-on vessel has the responsibility to maintain course and speed until it becomes apparent that the give-way vessel is not taking appropriate action to avoid a collision. When the stand-on vessel decides to alter her course, it is crucial to signal this change, especially if the give-way vessel is not responding. This helps to ensure safe navigation and clarity in communication between vessels.

This situation highlights the importance of sound signals as a means of communication on the water, especially in scenarios where visual cues may be insufficient due to visibility conditions or the position of the vessels involved. Sound signals thus play a crucial role in avoiding misunderstandings that could lead to collisions.