What action should be avoided by a stand-on vessel when it is evident that the give-way vessel is not acting sufficiently?

The action that should be avoided by a stand-on vessel when it is evident that the give-way vessel is not taking appropriate action is to avoid altering course.

In navigation, the stand-on vessel is responsible for maintaining its course and speed when it is clear that the give-way vessel is not making a safe maneuver to avoid a collision. If the stand-on vessel were to alter its course, it could potentially create confusion or undermine the give-way vessel's responsibility to take action. The stand-on vessel should remain predictable in its actions to maintain safety and allow the give-way vessel a clear opportunity to navigate safely away.

In this context, the other options involve actions that can either enhance safety or are irrelevant to the immediate navigation situation. For example, increasing speed may be appropriate in certain scenarios to maintain safe navigation, while using navigation lights is a requirement for ensuring visibility regardless of the situation. Sounding the horn is typically employed for signaling intentions or warnings but does not directly address the navigation responsibilities of the stand-on vessel under the circumstances described.