What is the most effective action to avoid a close-quarters situation?

Altering course alone if conditions allow it is the most effective action to avoid a close-quarters situation because it increases the opportunities for safe navigation. When both vessels are in a close quarters situation, one vessel altering its course can create more room and reduce the risk of collision. This action allows for clear signaling of intentions and can help communicate to the other vessel your plan for evasion, facilitating a better understanding of each other's movements.

Maintaining the current course and speed does not provide any preventative measures; instead, it keeps the vessels on a potential collision course. Waiting until the situation becomes critical is counterproductive, as this increases the urgency but limits the available options. Slowing down without altering course still leaves the two vessels on a potentially dangerous path, as speed reduction alone does not address the issue of proximity. Effective navigation relies on proactive measures, like altering course, to enhance safety and avoid dangerous encounters at sea.