Five or more short blasts on a vessel's whistle indicates that she is

• A. Signaling to pass on the port side
• B. In doubt as to whether another vessel is taking sufficient action to avoid a collision
• C. Not underway
• D. Changing course to starboard

Answer: (B)

Five or more short blasts is the whistle signal mariners use when they are unsure the other vessel will take sufficient action to avoid a collision. It’s a warning that expresses doubt about the other vessel’s intended maneuver and serves to prompt them to clarify or adjust course or speed. In practice, you’d use this when you’re in proximity with another vessel and you’re not confident they’ll handle the situation safely on their own. It’s not about not being underway or signaling a specific turn; it’s about signaling uncertainty and requesting action to prevent a collision.