When must the stand-on vessel use sound signals?

Answer: B — When she alters her course if the give-way vessel is not altering hers

The stand-on vessel is obligated to use sound signals when she alters her course if the give-way vessel is not making any alterations to hers. This is crucial to ensure clear communication between vessels, especially in situations where their intentions may not be immediately apparent. The stand-on vessel retains the right of way and, therefore, should signal her intentions when she feels it necessary to avoid a collision, particularly if the give-way vessel does not seem to be taking any action. In maritime situations, sound signals are a vital means of communication, particularly in conditions where visibility is limited or when vessels are in close proximity. This requirement emphasizes safety and the importance of maintaining awareness of all vessels' movements in the surrounding area. The other options presented do not meet the specific conditions that necessitate sound signals for the stand-on vessel. Passing another vessel at night or navigating in a narrow channel involves different responsibilities and situational awareness that may not require immediate signaling from the stand-on vessel. Similarly, approaching a port involves multiple regulatory considerations that do not directly compel sound signals from the stand-on vessel specifically in the context of altering course.