Parallel motion fenders incorporate a torsion arm mechanism which controls the trajectory of the fender whilst it is being compressed. The essence of this mechanism is to prevent the frontal panel from tilting when in contact with a ship’s hull. The trajectory path that the torsion arm follows controls the deflection of the rubber fenders, which are invariably cone types for these fenders. It also enables the cones to be stacked horizontally in a pair in series as this can reduce reaction forces by up to 60 per cent compared with conventional fenders. The panel on this fender always remains (near) vertical but can rotate in plan to accommodate large berthing angles – even at 20 degrees there is usually no loss in energy absorption. Applications include Ro-Ro and fast ferry berths, flat sided vessels such as bulk cargo and tankers, high tidal zones and monopile or load sensitive structures.
Their limitations would be: That these fenders are not suited to vessels which might contact the fender with large bow or stern hull flare angles, typically container ships, cruise vessels and naval vessels would fall into this category. These fenders really have only one degree of freedom, if struck from the top or sides they are rigid, in the case of side impact, unless the fender is able to rotate about its hinges the forces generated in the system can be extreme. Where belted vessels use these fenders, the frontal panel must extend vertically such that the belting(s) will always be in contact with the flat surface of the panel at any state of the tide, wave height or vessel laden condition, as over topping could lead to damage.