Question 1110Navigation General

The correct answer is A) anemometer. An anemometer is the instrument used to measure the apparent wind speed blowing across a vessel while underway. Apparent wind is the combination of the true wind and the vessel's own movement through the water, and an anemometer can accurately measure this combined wind speed. The other options are incorrect because a thermometer measures temperature, a wind vane measures wind direction, and a barometer measures atmospheric pressure, none of which are used to directly measure apparent wind speed.