When should the stand-on vessel change course and speed in order to avoid a collision?

The stand-on vessel should change course and speed when it becomes evident that action taken by the give-way vessel alone cannot prevent a collision. This principle is rooted in the responsibilities outlined in the Rules of the Road, which dictate that while the stand-on vessel has a duty to maintain its course and speed to the extent it can do so safely, it may need to take evasive action if it becomes clear that the give-way vessel is not maneuvering effectively to avoid the danger. This proactive approach promotes maritime safety by minimizing the risk of a collision, especially if the give-way vessel appears to be unaware or unable to take appropriate measures.

In this context, the other options may misrepresent when a stand-on vessel should act. For instance, changing course because of grounding risk or being in a confined channel does not specifically address the dynamics of collision avoidance with another vessel, whereas the primary scenario focuses on the interaction between the vessels involved. Therefore, the emphasis on ensuring safety through evasive maneuvering in response to a given situation is vital for navigating safely under the Rules of the Road.