R & D Flexible Shaft Coupling f/4" B/W, Hurth - 8HP/100RPM Capacity

The R & D Flexible Shaft Coupling for 4" B/W, Hurth with 8HP/100RPM capacity is a purpose-built marine component designed to absorb misalignment between your engine and propeller shaft. Built by R & D Marine, this flexible coupling uses a contoured polyurethane disc that flexes to compensate for engine movement and shaft runout caused by boat structure flexing or engine vibration isolation mounting. The design provides forward thrust compression while eliminating the torsional shock that rigid couplings transmit through the drivetrain.

The coupling's flexible disc features contoured geometry that clears bolt heads while maintaining the resilience needed to handle temporary misalignment without binding. At 8 horsepower and 100 RPM capacity, this coupling is rated for small- to mid-sized inboard and auxiliary engines common in displacement hull boats. The molded polyurethane material resists saltwater corrosion better than rubber and maintains flexibility across temperature ranges encountered in freshwater and coastal environments. Measuring 6 inches in overall dimension with a 2.15 lb weight, the coupling integrates into standard 4-inch shaft installations without requiring extensive modifications.

This flexible shaft coupling serves weekend cruisers, fishing boat operators, and anyone running auxiliary power systems where engine vibration or minor shaft deflection causes drivetrain noise or accelerated wear. Weekend fishermen benefit from quieter operation and reduced vibration transmitted through the hull. Serious boaters appreciate the extended life it provides to shaft seals, bearings, and engine mounts by absorbing shock loads that would otherwise accumulate damage over thousands of operating hours. Installation is straightforward on existing 4-inch Hurth transmissions, making it ideal for engine upgrades or coupling replacement on established systems.