Main engine torsiograph

A main-engine torsiograph is an instrument that measures the torsional vibration of the propulsion shafting, recording the angular oscillation superimposed on steady rotation as the engine’s firing pulses excite the crankshaft, shaft, and propeller system. It uses a seismic, optical, or strain-gauge pickup at the free end or flywheel to log amplitude against speed. The trace confirms the torsional vibration calculation, identifies resonance peaks, and defines the barred speed range that the governor must block. Class requires a torsiograph trial when the calculated stresses are near the allowable limit or the installation is novel.