Which device aids in determining the speed of wind at sea?

The anemometer is the device specifically designed to measure the speed of wind at sea. It typically consists of rotating cups or blades that are driven by the wind, with the speed of rotation correlating to wind speed. This information is crucial for navigating vessels, assessing weather conditions, and planning safe sea operations.

The compass is primarily used for navigation and determining direction rather than measuring wind speed. A chronometer helps in keeping accurate time, vital for navigation, particularly in fixing a position, but does not measure wind at all. Radar is used for detecting objects such as other vessels or landmasses and determining their distance and speed, but it does not provide direct measurements of wind speed.