area ratio, diameter or blade number, they all generated the same thrust at the same ship speed and shaft rate of revolutions by automatically adapting the effective pitch. This last requirement avoids the generation of ‘trivial’ propellers that operate at a lower rate of revolutions and nearly always have a better efficiency, masking the effect of improved blade design and introducing a bias in the comparison.


Using MARIN’s computer cluster, it was possible to generate and analyse over 10,000 new designs per day. The best pro- peller-hull combination was tested for its performance by model scale tests: a 7.5% power reduction at the design speed was identified and the shaft rate of revolutions did not change. This improvement is attributed to a reduction in resistance, an improvement in propeller-hull interaction by a lower propeller loading due to both the lower


thrust requirement and a larger propeller diameter, and lastly, an increase in propeller efficiency by an optimised loading distri- bution in the wake of the ship.


The propeller optimisation procedure can quickly show the relations between all the parameters and propulsion efficiency for a given wake field of a ship. But not only did MARIN find an optimum loading distri- bution and diameter, it also knew how much skew to apply to reduce thrust loading fluctuations. When results of the optimisation with a given propeller design are compared, it is possible to see how much its efficiency can improve and which parameters to tune.


Now that this first test case has been per- formed, MARIN is continuing to explore the automated propeller design. The process will be sped up by the use of genetic algorithms


report 15


and integrated into the daily design process. The EU project SONIC already presents the next challenge: optimising for both high efficiency, as well as low radiated noise.


References: Foeth, E.J. & Lafeber, F.H., Systematic propeller optimization using an unsteady Boundary-Element Method, 12th Int. Sym. Practical Design of Ships and Other Floating Structures, Korea, 2013.


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