Ship's Log

Tesla's ship's log, patented in 1919 under U.S. Patent 1,314,718, employed a rotating impeller or rotor towed in water to measure speed and distance instantaneously. Fluid drag transmitted torque magnetically or mechanically to a sealed indicator, providing real-time knots or miles-per-hour readings without cumulative errors from traditional logs.

Enhancing navigation accuracy, it offered reliability in varying conditions. Precursor to modern impeller-based logs and echo sounders, it advanced maritime instrumentation, influencing GPS-integrated systems for precise voyage tracking.