While underway in fog, you hear another vessel sounding two prolonged blasts every two minutes. What does this signal indicate?

Answer: B — vessel is drifting

The signal of two prolonged blasts every two minutes denotes that a vessel is making an effort to announce its presence while restricted in ability to maneuver. When a vessel sounds this signal in fog, it is typically indicating that it is either under way but cannot maneuver as easily due to factors such as size, draft, or operational restrictions. This signal is crucial during foggy conditions as it helps provide situational awareness for nearby vessels that may not be able to see one another. Essentially, it alerts others to the fact that a vessel is encountering limitations in its navigation capabilities. Understanding the signaling conventions is essential for ensuring safe navigation in reduced visibility conditions.