A prolonged blast on a whistle signals used by a power-driven vessel in fog lasts how many seconds?

• A. One to two seconds
• B. Eight to ten seconds
• C. Four to six seconds
• D. Three to four seconds

Answer: (C)

In restricted visibility, a power-driven vessel uses a single prolonged blast to signal its presence, and that blast should last four to six seconds. This duration is the standard definition of a prolonged blast, long enough to be clearly heard and distinguished from shorter, routine blasts. The other options don’t fit the standard: one to two seconds is too short to be considered a prolonged blast, eight to ten seconds is longer than the defined range, and three to four seconds is outside the recognized four-to-six-second window. So the best answer is the four-to-six-second duration.