Flexible Shaft Coupling for 4" B/W, Hurth - 8HP/100RPM CapacityThe R&D Flexible Couplings are fabricated from a contoured flexible disc molded 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 straps. In the unlikely event of a disc failure the steel straps make the coupling fail safe and ensure drive is maintained in both forward and reverse.To calculate power of coupling required:Horse Power of Engine x Reduction Ratio x 100 = HP/100RPM      Engine SpeedExample:Ford 150 HP at 2500 RPM with Borg Warner Velvet Drive 72C 2:1 Reduction RatioEngine Horse Power is 150 HP, Max Rated RPM is 2500, Reduction Ratio is 2:1150/2500 X 2 x 100 = 12hp per 100RPMCoupling required is 910-009The R & D Marine Flexible Coupling fits between the transmission output flange and shaft coupling. It is designed to protect a boat's drivetrain. The unit will reduce vibration, compensate for some misalignment, isolate the shaft and absorb shock loads.The flexible disc is machined from a resilient and durable polyurethane. It allows the unit to flex, absorbing vibrations and temporary misalignment of the shaft and engine due to movement of the engine or flexing in the vessel's structure.The polyurethane disc is backed up by two metal compression straps, one on either side of the flexible coupling. These metal straps hold the system in constant compression whether the drivetrain is in forward or reverse. This feature extends the life of the system dramatically.The R & D Marine Flexible Coupling will also absorb shockloads resulting from gear changes, or the propeller striking a submerged object. The polyurethane disk will distort with light shock loads and is designed to be sacrificial in the event of severe shock load, saving on expensive drivetrain repairs. If the disc is destroyed from massive shockload the metal compression straps keep the coupling intact ensuring that the drive system is functional in both forward and reverse.Why R&D Marine Flexible Shaft Couplings?Polyurethane flange creates a flexible barrier to reduce drivetrain noise and vibration to quiet your drivetrainAbsorbs transmission shock load caused by the propeller and high speed gear changes. This helps to reduce and avoid costly transmission damageFail safe design, both forward and reverse thrust is taken in compression from the steel straps, giving a durable design even in extreme conditions