While underway and in sight of another vessel, you put your engines full speed astern. Which whistle signal is true?

• A. One long blast
• B. Two short blasts
• C. Three short blasts
• D. Five short blasts

Answer: (C)

When you reverse course by putting the engines full astern, you need to warn nearby vessels that your vessel will be moving backward. The standard whistle signal for backing is three short blasts. This specific pattern communicates to the other vessel that you are reversing and may swing or move unexpectedly, so they can take appropriate action to avoid a collision.

The other signals correspond to different actions or conditions: a single long blast isn’t the backing signal, two short blasts indicate another maneuver, and five short blasts is the danger signal used to indicate distress or an urgent hazardous situation.