Investment casted strut drive & folding 3-blade aluminium-bronze propeller with shark-skin surface profile

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There is now a greater than 70% move from using the conventional horizontal shaft driven systems on motorised sailing boats to using the more modern vertical strut-drive systems. This move is driven by the market need for a low “sticker price” for competitive selling. However, strut-drive systems suffer from corrosion if the aluminum alloy of the vertical strut becomes, in any way, unprotected by its paint layers such that it comes into contact with seawater. This is especially true if a propeller of aluminium bronze is fitted prompting a galvanic reaction through the sea water. Copper-based anti-foulant paint is currently used but is damaging to the environment. Also, the strut gearing system is prone to failure as a result of torsional stress oscillations that are set up due to the firing impulses of the engine and the cyclical variations in power requirements of the propeller blades. This issue is not alluded to on purchase from a manufacturer who is only interested in repeat consumable item sales. From experience and through discussions with boat owners it appears boat owners can spend up to around £3,800 every 2 years replacing and installing a new strut and propeller due to electrochemical corrosion. Superprop Limited (SPL) propose developing a precision cast vertical strut unit with sacrificial anode and a cast propeller with a surface profile to reduce marine fouling. The combined unit will have a service in life of up to 15 years with substantial saving for boat owners from reduced drag, enhanced performance and reduced fuel use.