On my car carrier vessel, it was observed high vibration in engine room.  Can you advise me what is the problem?

In April 2017 we received similar question from our client. It was decided to send our two service engineers to conduct  investigation. 

Info Marine service engineers decided to carry out a multichannel global hull vibration measurement.  Accelerometers were localized on Main Engine free end top of the block, Main Engine drive end top of the block, intermediate shaft bearing, stern tube, ME top bracings, aft midship (above the propeller) and top of the vessel (roof of the highest deck). Measurements were performed at full range of ME speed from 37 to 117 RPM during Sea Trials on Adriatic Sea.

Analysis of vibration measurement of mentioned machines showed no particular problem. In spite of this, there has still been high vibrations.

Service Engineers decided to made closely some visual inspection and local measurements of engine room area to find the source of the abnormal vibrations.

It was noticed some local resonances.  Some constructions were not properly strengthened and supported. Construction vibrations were excited by main engine. Bolts of main engine platform were not properly tightened, some of them were loosen and it was possible to remove them by hand. Shipyard was asked to retighten all bolts of main engine platform with proper torque.

Below we present some of the problems, that has been found:

It was observed that top of platform of LT, Fire, GS and Ballast motors highly vibrates even when pumps are not operating with. The  engine platforms were found mounted on soft rubber dumpers which multiplied low external vibrations to very high level. Dual channel vibration measurements shows increasing value of the platform vibrations with its high, and its level become dangerous for machine condition above rubber dumpers. Was recommended to remove those dumpers or replace them with more harder ones which will allow to dump frequencies responsible for exciting high vibrations on platform structure.

It was noticed that steering gear motors and pumps are vibrating with clearly visibly displacement. Platforms construction needs to be improved to provide adequate support for electric motor and pump free ends and reduce the risk of premature failure of the equipment due to very high vibrations.

  

It was noted, that floor in control room have high vibrations with regard to habitability and comfort. Measurements according to ISO 6954 were taken and vibrations were over the limit. Investigation have place, to find the source of problem. Engineers take additional measurements on the floor level, and decide to look deeper, floor plates were removed and were decided to check construction of the floor platform. Investigation shows that floor was mounted on soft elastic dumpers.  It was performed dual channel measurement in this case. Results shows that vibrations on ship structure side are much lower than on floor platform. It suggest that floor construction have low stiffness and  excite vibration from environment. It was recommended to consider change of construction to reduce level of vibration.

 

During visual inspection and spot check vibration measurements, engineers observed many points which vibrate with visible displacement.  Control cabinet, electronics, pumps, pipes, coolers and so on. We recommend to install additional supports for vibrating equipment to improve stiffness of its construction. Many supports were installed and situation getting better. Our recommendation allow Owner of the vessel avoid many additional cost which could appear due to premature failure of the equipment.