Like in road- transport- technology only approximately 26% of the prime energy (fuel) acts on this PE The employed fuel converts to losses in the different steps of transformation,around 35%alone on the propeller (Data Fjellstrand AS).The steep acceleration of the towing-power with speed is shown too. Only 2 knots [3,7km/h]more than doubled the kW needed, with proportional influence on the fuel consumption.