External unbalances are caused by the inertia of the rotating unbalanced masses of the engine - The most common external unbalanced moment is the 2^nd order moment acting in vertical direction only and with a frequency corresponding to two cycles per engine revolution.



The problem is most frequent on 4 to 6 cylinder engines, furthermore engines with 10-14 cylinders has an external unbalanced 4^th order moment. In in most cases these engines are delivered with a built in mechanical 2^nd order moment damper. The location of the vessels zero hull node can enhance the 2^nd order reaction forces causing hull vibrations.






As an alternative to "built in" flyweights in the main engine - G&O are offering a solution where the outbalancing source (compensator) will be placed in the steering gear room. The advantage of a longer lever arm between engine and compensator is utilized and consequently much smaller unit can be used. Furthermore the unit is electrically driven and independently from mechanical connections to the main engine.

On e.g. tankers the natural hull frequency changes dramatically when the vessel is in either full load or ballast. In one condition the engine could create a resonance and in the other condition there could be no resonance present. By using an independent and electrically driven unit it is possible to operate the unit only when needed.