What action should both vessels take when meeting on nearly opposite courses?

When two vessels are meeting on nearly opposite courses, the correct action is for both vessels to alter course to starboard. This maneuver is established by the rules of navigation to avoid collisions and ensure safe passage. By veering to starboard, both vessels will pass on the port side of each other, which is the convention that promotes safety and predictability in maritime navigation.

This practice stems from the understanding that most vessels are equipped in such a way that they can easily maneuver to the right (starboard) when encountering another vessel. This convention minimizes the risk of misunderstandings that could lead to dangerous situations at sea. Additionally, it provides a clear and standardized method for vessels to navigate around one another, supporting safer interactions in crowded or narrow waterways.

The other options do not align with established navigation rules for this scenario. For instance, altering course to port could lead to a collision if both vessels choose to do so. Maintaining the current course or only reducing speed does not adequately address the risk of collision because the vessels would continue on their current path without a change in direction, which is crucial when two vessels are on intersecting tracks. Therefore, altering course to starboard is the safety-oriented and rule-compliant action for both vessels in this situation.