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WRITE TO Each time the marina staff move my boat to their maintenance berth, the shaft comes out of its coupling in reverse. I’m relatively new to boating and it hasn’t been a problem when out cruising. What causes it, and what can be done to secure it? Is it likely to be damaged?
Possibly the yard hands use more revs than you do (perhaps to use ‘propeller walk’ to help position the boat). From your photo it’s a simple
Awebsite clamp-on type secured with four bolts. If the yard loosened the bolts, replaced the shaft and tightened them correctly after the first time, then the shaft, coupling or both might be worn. The shaft and coupling bore size need measuring.
You have no flexible coupling so if the engine is flexibly mounted it will ‘work’ the coupling on the shaft unless you are using a packless stern gland (which you do) and Cutless rubber shaft bearings (which I expect you have). With this set-up it is vital that the coupling and engine are within 0.05mm in both axial and angular alignment. Old flexible engine mounts might have collapsed and put the engine out of alignment.
When you undo the half-coupling and push it back the shaft is only supported by rubber so will not only drop but will also have a fair amount of radial movement.
Before aligning such shafts I always rig up wood and some nails to hold the shaft in the absolute centre of the play while I move the engine to get that 0.05mm of alignment.
Canal Boat Magazine, Archant Specialist, Evolution House, 2-6 Easthampstead Road, Wokingham, RG40 2EG