Engine power

To this day, the performance specifications for boat engines vary. Boat manufacturers and sellers like to claim the highest possible engine power. However, the actual power available is often lower. Why is that?

Until 1972, engine power was specified in horsepower. From 1972 onwards, kW (kilowatts) was used. At that time, the basis for calculating horsepower was very different in the various countries. In America, SAE horsepower was common. By using unrealistic measurement methods, in which the engines ran on the test bench without auxiliary units such as alternators or pumps, particularly high power values could be specified.

While the Perkins engines used by Storebro at the time were listed with DIN horsepower in the price list, Volvo-Penta liked to use SAE horsepower for the output.
With the change of the Swedish Storebro price list from No. 48 (1975) to No. 49 (1976), Storebro used the same unit for all engines. These now referred to the power on the propeller shaft.
The new values cast a new light on the popular Volvo Penta MD32. The significantly lower power compared to the Perkins engines, especially the supposedly comparable Perkins 115, ultimately explains the big difference in driving performance.

Another performance issue was the difference between flywheel power and propeller shaft power. With newer engines in the 300-400 hp range, the loss is about 5 to 20 hp. This value depends on the type of gearbox installed.