TPD1317e Chapter 2 Propeller Shafts and Couplings 2.1 Propeller Shafts It is recommended that all engines are mounted on flexible mountings, which will reduce the transmission of noise and vibration, and will prevent hull movements resulting in forces being applied to the engine. The responsibility for the design and installation of the transmission system connected to the marine gearbox lies with the boat designer, the boat builder, the naval architect or the engine installer. It is recommended that a Torsional Vibration Analysis (TVA) is carried out on the complete drive system. Mass Elastic Data on the engine can be provided on request from Sabre Engines Ltd.
The following observations are offered, to show some of the systems currently in use. Figure 1 shows a simple arrangement, where the propeller shaft is supported only by the gearbox coupling and an outboard rubber bearing at the propeller end. Entry of water into the boat is prevented by a shaft seal, which must be flexibly mounted to allow for engine movement. A flexible shaft coupling is fitted to the gearbox coupling, to allow momentary angular misalignment in operation. This system is only suitable for applications where the speed, diameter, and unsupported length of the propeller shaft will not induce ‘whirling’ (i.e.
the centrifugal force generated by the speed of rotation is not sufficient to bend the shaft into a bow shape). Reinforced rubber hose Graphited asbestos string Stuffing box е Flexibly mounted shaft seals Shaft Cutless bearing Flexible shaft coupling Flexible mountings Page