Which action should be taken if both vessels involved in a close-quarters situation cannot determine risk of collision?

Answer: C — take evasive action

In a close-quarters situation where neither vessel is able to determine if there is a risk of collision, taking evasive action is essential for ensuring safety. The International Regulations for Preventing Collisions at Sea (COLREGs) emphasize the importance of proactive measures to prevent accidents when uncertainty exists regarding the interaction between vessels. When vessels are close together and the risk is ambiguous, maintaining the current course or increasing speed may create further uncertainty and can likely lead to a collision. Assuming there is no risk can lead to complacency, which is dangerous in such scenarios. Therefore, taking evasive action is prudent; it allows for the opportunity to alter the vessel's course or speed to avoid potential accidents, thereby prioritizing safety on the water. Ultimately, it aligns with the general principle of navigating safely and responsibly under circumstances where potential hazards cannot be clearly identified.