Which electronic device helps in determining a vessel's speed?

The device that assists in determining a vessel's speed is an electronic log or speed log. This instrument is specifically designed for measuring and recording the speed of a vessel over water, which is crucial for navigation and operational efficiency. The speed log can utilize various technologies, such as a pitot tube or electromagnetic sensors, to provide real-time data about the vessel's speed.

While other devices have navigation-related functions, none are primarily intended for directly measuring speed like the speed log. For instance, a compass is primarily used for determining direction and does not provide speed information. Radar systems are often employed to detect other vessels and obstacles and can indirectly assist in navigation but do not measure a vessel's speed. A GPS receiver, on the other hand, can calculate speed based on positional changes over time; however, its primary function is to provide location information rather than dedicated speed measurement as effectively as a speed log does. Therefore, the electronic log or speed log is the most appropriate choice for this function.