Final answer:
A stand-on vessel must take action when it determines that the other vessel is not taking appropriate action to avoid a collision. Maritime rules require the stand-on vessel to maintain course unless the give-way vessel fails to follow the rules, at which point evasive action is necessary.
Step-by-step explanation:
In order for a stand-on vessel to take action in a situation, she must determine that the other vessel is not taking appropriate action. A stand-on vessel is the boat that has the right of way during navigation and according to maritime rules, it is obligated to maintain its course and speed. However, if the stand-on vessel assesses that the give-way vessel (the one that does not have the right of way) is not taking proper actions to avoid a collision, the stand-on vessel is then required to take evasive action to prevent an accident.
In the maritime context, the actions of vessels and the decisions taken by their crew in order to avoid collisions are regulated by what is known as the International Regulations for Preventing Collisions at Sea (COLREGs). The stand-on vessel's duty to hold course and speed holds true unless it becomes apparent that the give-way vessel is not maneuvering as it should to ensure a safe passage.