Abstract: A system designed to periodically obtain a precise measure of the impact of all factors which may be degrading a ship's operational performance. A complete trial of a ship consists of several test runs of the ship in opposite directions during which the propulsion plant shaft horsepower is maintained steady. If the net drift during the relatively short period of the trial is constant then test runs in opposite directions cancel the effects of current and wind on that trial. By combining the results of runs on reciprocal headings, ship speed through the water is obtained to builder trial accuracy. During a run, the system acquires data from the ship's gyrocompass, a torsionmeter which is mounted on the propeller shaft, a fuel flow meter, a fuel line thermocouple and the ship's Loran receivers. The system processes time difference readings from the Loran receivers to obtain ground speed.