Shaft brake (hydraulic)

A hydraulic shaft brake is a disc or band brake, hydraulically applied, that locks the propulsion shaft to stop it turning, fitted on the intermediate shaft or at the gearbox. It holds the shaft for propeller, stern-seal, or gearbox maintenance, and on diesel-electric and shaft-generator vessels it lets the shaft generator run as a PTI motor or supply power while the propeller is stopped or the main engine is declutched. A trailing propeller can windmill the shaft in a current, so the brake also prevents reverse rotation when the engine is stopped. Caliper pads clamp a brake disc on the shaft; class requires the holding torque to exceed the windmilling torque.