Brake horsepower for tugs

Brake horsepower (BHP) for tugs is the power measured at the engine output shaft, at the flywheel or coupling, before any transmission, gearbox, or propeller loss. It rates the diesel prime mover, not the useful pull the tug delivers at the towing hook. The figure that matters operationally is bollard pull, the static thrust at zero speed, which a conventional tug develops at roughly 10 to 13 kg of pull per BHP and a modern azimuth-stern-drive or tractor tug at a higher ratio because of nozzle and thruster efficiency. Port authorities and terminals specify minimum bollard pull, not BHP, for ship-handling and escort work. Quoting BHP alone overstates capability because it ignores propulsive efficiency.