While underway in fog, you hear a vessel ahead sound two prolonged blasts on the whistle. Which action should you take?

When you hear a vessel sound two prolonged blasts on the whistle while underway in fog, it indicates that they are either a power-driven vessel operating in restricted visibility or they are signaling their intent to overtake another vessel. The requirement for vessels in fog is to communicate their presence and intentions using sound signals and to take appropriate action to ensure safety.

The recommended action aligns with maintaining a watch, navigating safely, and ensuring that all vessels are aware of each other’s presence while visibility is limited. Sounding your fog signals until the other vessel is sighted is prudent; it conveys that you are actively monitoring the situation and are prepared to respond as necessary. This allows for continued communication and alertness between vessels, making it safer for all parties involved.

In contrast, increasing speed could lead to decreased maneuverability or potential collisions since fog already limits visibility. Sounding one prolonged blast in reply does not conform to the appropriate response for two prolonged blasts, which typically indicates a recognition of intention rather than a direct reply. Changing course immediately could also increase the risk of collision if not done in a deliberate and coordinated manner, especially when the intentions of the other vessel are unclear.

Thus, the most appropriate and safe action is to sound your fog signals until you can clearly identify