If you are the stand-on vessel in a crossing situation, you may take action to avoid collision by your maneuver alone. When may this action be taken?

The correct answer emphasizes the responsibility of the stand-on vessel in a crossing situation to take action to avoid collision only when it becomes clear that the give-way vessel is not taking the necessary steps to avoid a collision. This means that the stand-on vessel should maintain its course and speed until it is evident that the other vessel, which is obligated to yield, is not responding appropriately.

This principle is rooted in the rules of navigation which prioritize the actions of the give-way vessel to ensure safe passage. The stand-on vessel should remain on its planned path to avoid confusing the give-way vessel, allowing it to take the appropriate action. Only after determining that this vessel is not reacting properly should the stand-on vessel take evasive action, ensuring that safety is prioritized.

Taking action at any time when it feels appropriate could lead to confusion between vessels, possibly resulting in an accident, as each vessel might not understand the other's intentions. Waiting until extremis would mean waiting until the situation is dangerously close to a collision, which is not ideal for ensuring safety. Taking action solely based on assessing that the current course would cross ahead of the other vessel does not necessarily consider whether the give-way vessel is responding appropriately, which is essential in these situations.