Airborne Composites has supplied the Royal Netherlands Navy with a composite main propeller for an Alkmaar-class minehunter.
Airborne say that this is the first time in the world that composite materials have been used for a maritime main propeller of such power (about 1400 kW). The propellers were delivered to the Navy in September 2010 and test runs will start at the end of 2010, continuing throughout 2011. The Royal Netherlands Navy has ten Alkmaar-class minehunters, developed in the 1970s by the Navy in cooperation with its French and Belgian counterparts.
Erosion is a big problem in bronze ships propellers, explained Wiard Leenders, Managing Director of Airborne Composites. It interferes with the geometry of the blade surface, giving rise to turbulence and hence to vibration and noise. This effect on the acoustic signature of the vessels is particularly undesirable in minehunters, which have to operate very silently in order not to trigger the mines they are hunting. Frequent inspection and maintenance is the only way of ensuring a safe working environment in this case. The necessary maintenance is very expensive, and reduces the operational availability of these vessels. The use of composite materials for the ships propellers offers a way out of this impasse, Wiard Leenders stated.
Hydrodynamic tests at the Marin maritime research institute in Wageningen were so promising that the Royal Netherlands Navy commissioned a follow-up study at Airborne. This focused on the possibility of using the orientation of the fibres reinforcing the composite material in order to get propeller blades that adjust their position in response to the load on them, thus obtaining a hydroelastic propeller. These propellers are more quiet in use, and have a higher efficiency which may lead to fuel savings of a few per cent. These fuel savings have generated increasing interest in these flexible composite propellers in civilian shipping circles, Wiard Leenders went on.
The composites used for this purpose are carbon-fibre-reinforced epoxy resins.
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