Your vessel is on course 150°T, speed 17 knots. The apparent wind is from 40° off the starboard bow, speed 15 knots. What is the speed of the true wind?

Correct Answer: Option C — 11.0 knots

True wind is determined by vector addition of ship's velocity and apparent wind vector. Using standard relative wind triangle vector resolution (or Bowditch tables), a 15-knot apparent wind 40 degrees off the bow with 17-knot ship speed yields 11.0 knots true wind.