Marine coupling shows its flexibility

Centa Transmissions had to overcome a significant gearbox location problem when it was asked to substantially reduce noise and vibration from the transmission of "Sea Shepherd".
Yorkshire-based flexible coupling manufacturer Centa Transmissions had to overcome a significant gearbox location problem when it was asked to substantially reduce noise and vibration from the transmission of "Sea Shepherd", the new 15.25m pilot launch for the Aberdeen Harbour Board. Propulsion on the vessel is by twin resiliently mounted Scania DI12 41M engines developing 265 kW at 1880rev/min, driving close coupled twin disc MG 5019SC gearboxes having a 2.45:1 reduction ratio, PTO clutch and hydraulic pump. Centa's solution considered the Centaflex AGM coupling design, but designers came up against a general problem with most marine gearboxes, in that when the gearbox was originally designed, no thought was given to the use of flexible couplings and the oil pump was positioned very close to the output flange.

On the gearbox in question, the output flange is 7.25in diameter and only a coupling of maximum diameter 7.5in would fit without fouling the oil pump.

A 4in spacer would have been required to clear the pump and in addition a manually clutched PTO and hydraulic pump required an even longer spacer at 500mm.

A spacer of this length plus the Centaflex AGM coupling would have been too long for the installation and would have upset the flexible mounting arrangement, so a composite universal joint and Centaflex Series A Cardan shaft was developed.

To achieve the required noise and vibration insulation level, a flexible element providing a long articulation length allows significant engine movement to reduce noise and vibration, without the need for additional spacers.

Dennis Davidson, of Murray Cormack Associates, who designed the vessel said: "Centa's coupling design achieved a very low noise level throughout the boat".

Centa manufactures a wide range of flexible couplings and driveshafts with torque capacities up to 1MNm, covering every application from canal and riverboats to workboats and larger sea-going vessels.