In cases where it is not possible to outbalance the source of a vibration, the second best choice is to outbalance the local vibration (symptom) where it occurs. The advantage of a lever arm between the inducing source and the compensator is utilized and consequently a relatively small imbalance is required to outbalance the local vibration.
Hull beam vibrations are dealt with by placing a horizontal compensator at a reinforced area of the hull and create a corresponding counterforce – the compensator will be synchronized e.g. to the main engine or propeller (source).
Resonances related to propeller, axial thrust and external 2nd and 4th order external moment can all be reduced – there are many possibilities:
Propeller induced vibrations can either be treated as hull beam vibrations or in some cases it is possible to place a vertical compensator above the propeller and thereby outbalance the source.
The below confirmation test was made on a MAN-B&W main engine, type: 10K98MCC installed in a 6.000 TEU container vessel. A C-20H compensator was installed in a small provision room on one of the upper decks. The measurements were recorded by horizontal transverse and longitudinal accelerometers placed on the navigation bridge. The vibration level was reduced from 24 mm/sec down to less than 1 mm/sec in the resonance area.
