Shaft slip

Canal Boat - - Back Cabin: - CHRISFEAST, TONY REPLIES… CB

QIf you have any boat­ing re­lated query, then our team of ex­perts on all things boat­ing are here to an­swer it EMAIL:

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?

via the

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

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