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 causes this guide force moment. Engines with 7-14 cylinders are having a guide force X-moment, which is identified as a horizontal twisting 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. In guide force x-moments two counter rotating compensators are required. The advantage of a lever arm between the compensator is utilized and consequently a relatively small imbalance is required to outbalance the source.

The below illustrated confirmation test is made on a Wärtsilä-Sulzer main engine, type: 8RT-flex96C on a test bed. Two C-40H compensators are installed on the gallery brackets of the main engine outside cylinders no. 1 and no. 8.



The measurements were recorded by horizontal transverse accelerometers placed on cylinder frames no. 1 and no. 8 - the vibration level was reduced from 52 mm/sec down to less than 10 mm/sec in the resonance area. Additional reductions can be expected once the main engine is installed in a vessel and a specific fine-tuning of the system is possible.