The purpose of the cross heads of a two stroke slow speed diesel engine is to convert oscillation forces into rotation forces. The transverse reaction forces that occur when the engine crossheads are acting on the engine upper structure cause this guide force moment. Engines with 4-7 cylinders are having a guide force H-moment, which is identified as a transverse rocking movement of the engine top.



Conventional countermeasures such as top bracings, hydraulic dampers and reinforcement of the hull structure do have limited impact on this type of moment. Often the use of such countermeasures only tends to transfer the guide force moment from the engine into other parts of the vessel and new resonances are likely to occur. The source of the vibration problem (the guide force moment) is still present and the symptoms (resonances) have just changed character and location.



Alternatively G&O are offering a solution where the outbalancing source (compensator) will be placed directly on the inducing source (main engine) - thereby the guide-force moment is eliminated and will be isolated from spreading into other structures and components. The advantage of a lever arm between compensator and the engines "rocking point" is utilized and consequently a relatively small imbalance is required to outbalance the source.

The use of a horizontal vibration compensator brings you as close as you can get to a guide force free engine – enabling new perspectives when designing vessel and corresponding main engines. E.g. a 5 cylinder main engine equipped with a G&O compensator will have guide forces moments significantly lower than a 7 conventional cylinder engine. Today it is therefore possible to utilize the many operational and economical advantages of 5 cylinders and at the same time enjoy the low vibration characteristic of a 7 cylinder in one and the same engine.

The below illustrated confirmation test is made on a MAN-B&W main engine, type: 5S80MC installed in a 135.000 dwt tanker. A C-40H compensator was installed on the gallery brackets of the main engine outside cylinder no.: 5.



The measurements were recorded by a horizontal transverse accelerometer placed on the main engine cylinder no.3   - the vibration level was reduced from 62 mm/sec down to less than 3 mm/sec in the resonance area.



Horizontal vibration compensator installed directly on the main engine gallery brackets.