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T


he Holtrop-Mennen method has proved to be highly effective at the initial design stage to establish


the still water performance and for estimat- ing the required propulsive power. For some readers that may not be familiar with the Holtrop-Mennen method, the pair worked on developing a numerical description of ship resistance and propulsion, using basic hull dimensions. The total ship resistance is subdivided into components and each component has been evaluated by multiple regression analysis. Holtrop and Mennen examined almost a thousand model tests and a few hundred trial measurements from the MARIN database.


However, these two very modest men certainly did not set out to take the hydro- dynamics world by storm. Jan went into the industry after finding that a mathematics degree was simply “too abstract”. He then found his way to a shipyard and enjoying a more hands-on approach, this stimulated him to study Naval Architecture. Perhaps Frits was more destined to work at MARIN. Frits used to while away his youth watching canal traffic and he always enjoyed making models of barges. Fortunately one of his teachers saw potential and suggested he go off and study for a maritime career.


True pioneers So both found themselves at MARIN in the early seventies and they were asked to go to the then new Depres- surised Towing Tank and find a modern way to carry out data analysis with a focus on the extrapolation of model tests. Initially, the method was designed for internal pur- poses so MARIN could make more accurate predictions. “I knew something about the traditional power prediction methods but it was how to change these into modern extrapolation methods,” says Frits.


1983


Start potential flow calculations for hull form optimization


Courtesy STX Europe


“It really was a totally new area. Ships were rapidly becoming bigger and bigger and traditional methods of extrapolation were becoming more uncertain,” adds Jan.


“Miracle method” A new “miracle method” was definitely needed, stresses Frits. After analysing all the components numerical formulations were developed from which scale-effects could be derived and by adding a few additional formulas, we could come up with a general power prediction method, Frits says.


Using the general extrapolation method of William Froude a percentage correction is to be made for correlation but for several classes of ships nobody knew accurately what that correction should be, says Jan. A large negative correction was unthinkable but it was sometimes encountered in the correlation of model tests and in full-scale trials of the biggest ships. Under the component-based approach scale effect corrections could be made for the viscous


resistance and the efficiency elements. “It was much better to make a distinction between these components as it gives a more rational approach,” adds Jan. Of course, one thing that was crucial to the development of the Holtrop-Mennen method was having a very good database, points out Frits and that was just what he had access to at MARIN. A high quality data- base, with hundreds of model experiments and full-scale trials was vital, he says. In the Depressurised Towing Tank with new test equipment in “unfriendly conditions” there was an urgent need to have adequate checks on the results, they add.


The two started with the system analysis and then reanalysed the model tests and the full-scale trials. The target was to have a component-wise prediction method that would show the difference between model and full-scale to serve the extrapolation of the model experiments, they explain. The reaction was really quite a surprise, the two admit. After the method was first


1985


Model test of tow-out of Troll; concrete platform in 336 m water depth


report


7


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