Shaft & Gearbox Losses

Convert brake power (engine output) to delivered power at the propeller by subtracting shaft-line and gearbox losses. Needed whenever an SFOC-based fuel model produces brake power but the hydrodynamic stack wants delivered power.

DesignPropulsion

Inputs

Brake power (engine output)kWShaft-line efficiency $η_S$–Direct-coupled two-stroke ≈ 0.99; long shaft lines with two bearings ≈ 0.98.Gearbox efficiency $η_G$ (use 1.0 if none)–

Total transmission efficiency

0.9900–

Delivered power

9,900kW

Power lost

100kW

Formula, assumptions, and limits

$$P_D = P_B \cdot \eta_S \cdot \eta_G$$

ITTC notation. If propulsive coefficient is needed downstream, multiply $P_D$ by open-water and relative-rotative efficiencies. This page stops at the shaft because SFOC is invariably quoted on brake power.

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