The MC 41SK can either be built in aluminium or in steel. In the case of aluminium construction, the keel is special. It consists of a structured thick-walled box with the hydrofoil shape required with lead poured inside, in order to obtain the necessary weight. In the case of steel construction it is specified a cast iron keel, with identical outside shape as the aluminium one, and also having the same weight. The lifting mechanism is also identical, consisting of a hydraulic piston connected to the keel by means of spectra ropes.
MC 41 SK aluminium keel box with structure, however still missing to install the portside plating. The emptuy spaces will be filled with lead. Courtesy Ilha Sul Boatyard.