Isolator Internal Resonance and Radiated Noise from Ships

Reducing the radiated noise from ships is becoming increasingly important as ship -builders aim to reduce the disturbance to marine life, passengers and crew. A major contributor is on-board machinery which typically radiates noise to the water column from both structure-borne and air-borne transmission paths. Problematic machinery is often decoupled from the hull by supporting it on resilient isolation mounts. This paper predicts the effect of isolator internal resonance on the underwater radiated noise by considering a typical marine diesel characterised by source levels estimated from empirical relationships. The structure-borne and air-borne transmission paths are resolved individually using approximate analytical methods. It is subsequently demonstrated that the reduction of isolator internal resonances could provide a significant reduction in the underwater radiated noise from ships.