How often should a vessel that is underway and making way in fog emit a signal?

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

Answer: (B)

In fog, ships use specific whistle signals to convey what they’re doing. A power-driven vessel that is underway and making way should sound a single prolonged blast, repeated at intervals not exceeding two minutes. The prolonged blast should be long enough to be clearly heard (typically about 4–6 seconds). This signal clearly communicates that you are moving and continuing on your course, helping others decide how to respond to avoid a collision. The other patterns—one short blast, two prolonged blasts, or five short blasts—do not represent a moving vessel making way in restricted visibility, so they’re not the appropriate signals in this situation.