Flexible Shaft Couplings This range of flexible couplings consist of a contoured flexible disc moulded in, tough yet resilient, new type polyurethane. The contoured disc gives clearance for the bolt heads, and is able to flex freely to take up any temporary misalignment of the engine and shaft due to flexing of the boat structure or the engine moving on its rubber vibration isolation mountings. Forward thrust is taken in compression on the disc between the two half couplings, and reverse thrust is taken again in compression on the disc between the two fail safe straps. In the unlikely event of a disc failure the steel straps make the coupling fail-safe and ensure drive is maintained both forward and reverse.