We have, however, experienced one case of a thin-shell bearing failure in a K80MC-C engine. In this case we observed that our installation recommendation had not been fully observed, and large changes in the bearing load were seen at different loading conditions of the vessel. The cure was replacement of the white metal bearings with Sn-Al bearings with higher fatigue strength. The engines have now been running for about two years without any bearing problems. Subsequent engines for the same ship type were installed according to our instructions, and their white metal bearings have been performing well.
The original thick-shell main bearing has in the past given rise to a number of cases of damage. This has initiated a number of design changes of the bearing itself, but another important investigation was initiated - the cogency between the main engine and the hull.
These investigations have caused us to make our alignment procedure more stringent and to emphasise the importance of using it. The investigations are being continued in cooperation with the classification societies, and the results are valid for any type of main bearing.
3.6 Environment
Environmental friendliness is an important development item to which the author's company has dedicated much effort over the last two decades.
Exhaust gas emissions are dealt with in Ref. [4], but today also noise is an important environmental issue.
The noise from modern two-stroke diesel engines is mainly generated in the turbocharger compressor and turbine. The increased charge air flow and pressures have made the turbochargers noisier while, at the same time, the requirements for limiting noise levels in the engine room are becoming stricter.
Most large ships of today are specified to fulfil the requirements of IMO for noise level, which means a level lower than 110 dBA. Stricter requirements are also seen, such as those given by the Danish maritime authorities, who stipulate that noise suppression countermeasures should target a noise level below 105 dBA.
Although generated in the turbocharger, the noise spreads along the airways and radiates downstream from compensators, charge air pipe, cooler units, scavenge air space, and exhaust pipe. Upstream, a certain amount of the noise passes the silencer in the compressor inlet.
For the large engines, we have introduced an extensive noise insulation of the engine in the area in which noise is radiated, so as to cater for any specified noise requirements, see Fig.10.
The turbocharger makers are working intensively on designs of compressors and turbines which can reduce the generation of noise, and on improved inlet silencers and insulation of the turbocharger casing.
The requirements for low noise levels have been set, and it has been confirmed that these can be met.
4. TESTBED AND SERVICE RESULTS FOR K98
The first K98MC engine, a seven-cylinder unit, was tested in August 1999, and the operating hours on testbed were about 150. An additional test was carried out on a 10K98MC-C in October 1999.
As has been our usual practice, the prototype test was very comprehensive. The results were very satisfactory.
The component inspection after the testbed trial and the type approval test showed excellent results, and the 7K98MC was furthermore inspected after approx. 800 hrs. in service.
