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March 14 2002

BV sorts out box ship shafting problem
Classification society Bureau Veritas has provided specialist expertise to help Korea's Hyundai Heavy Industries resolve propeller shaft problems on a series of 7,200 TEU mega containerships it is building for Germany's Hapag Lloyd.

The ships, which are being built to GL class, have 92,000 hp main engines, the largest yet installed in a containership. A previous similar size containership from HHI suffered stern tube wear problems due to problems with the shaft alignment. BV says its specialist shaft alignment team has solved the problems on that ship, and for the rest of the series of new ships.

"When you have very large engines installed in modern optimized hull structures, you must pay a lot of attention to the shaft arrangement, or you are guaranteed to have trouble once the ship enters service," says Jean-Michel Forestier, head of BV's special services team. "In this case we performed very detailed calculations to set up the correct arrangement. It is one of a number of cases involving very large engines in modern ships that we have dealt with recently. We have unique experience in this field, and as ships continue to get bigger, there will be more and more demand for this expertise."

In this case, BV calculated the elasticity of the 950 mm shaft and its interaction with the elasticity of the aft end hull structure when the vessel was at full load. The calculations have to take into account oil film thickness and reactions, in order to optimize alignment conditions and bearing arrangements for static and running conditions.

"The basic problem is that as the installed horsepower of ships has grown, so the propeller shaft has had to get thicker to cope with the power. Now we have reached a stage where the shaft and engine are stiffer than the surrounding hull, and the expertise to design the bearings and supports to cope with that is not sufficiently widespread," says Forestier.