In a narrow channel, an overtaking vessel, which intends to pass on the other vessel's port side would sound—

• A. one prolonged blast.
• B. two prolonged followed by two short blasts.
• C. three short blasts.
• D. one prolonged followed by two short blasts.

Answer: (B)

Informed signaling for overtaking is built to be unmistakable even in tight spaces. When a vessel intends to pass another on the other vessel’s port side, the standard whistle signal is two prolonged blasts followed by two short blasts. The two long blasts clearly indicate an overtaking action, and the subsequent two short blasts specify that the pass will happen on the port side. This pattern is designed to be distinct from other signals and to remove ambiguity in a narrow channel where precise understanding of each vessel’s intentions is crucial for safe movement.

Other patterns do not convey the same port-side overtaking intention, so they would not correctly communicate the planned passing side in this situation.