What does the fog signal of one prolonged blast followed by two short blasts indicate?

• A. A vessel towing
• B. A vessel underway in fog
• C. A vessel not under command
• D. A vessel restricted in ability to maneuver

Answer: (D)

In restricted visibility, ships use standardized whistle signals to convey their state. A single prolonged blast followed by two short blasts identifies a vessel restricted in her ability to maneuver. This tells other vessels that the vessel cannot easily alter course or speed to avoid danger because of ongoing operations or constraints (such as dredging, towing, or other activities that limit maneuverability). Because of this limited ability to maneuver, other vessels should proceed with extra caution and keep well clear. This same pattern is used to communicate RIM status so nearby vessels understand how much room they need to give.