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

Correct Answer: Option A — A vessel is drifting

Rule 35(b) defines the signal of two prolonged blasts as being sounded by a power-driven vessel that is underway but making no way through the water. In practice, this indicates the vessel is stopped and drifting, as it has no propulsion or headway relative to the water.