taffrail log

Noun

 * 1)  A mechanical device dragged from the stern of the vessel that indicates the vessel's speed through the water; usually consists of a propeller, a reading unit and a stiff line connecting them.

Translations

 * Finnish: laahusloki, patenttiloki
 * Hebrew:
 * Russian: вертушечный лаг, гакабортный буксируемый лаг