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First aid for a split half coupling on our boat


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Because of ill usage by either the previous owner or an over exuberant marine engineer, recently prop walking the boat, the drive shaft in our 52' narrow boat has worked loose on two previous occasions when others were using the boat. Worryingly it happen again to us whilst we were on the lower reaches of the River Soar approaching the Trent. Fortunately I had sufficient way to reach, just, the bank side and securely moor the boat.

 

The shaft had worked loose from the half coupling thus causing the bolts on both this and the drive plate to the gearbox to loosen. I slacked back all the nuts & bolts and this enabled me to push the shaft fully back into the coupling. In so doing I noticed that the coupling end of the shaft is badly scored. I then tightened the nuts & bolts of the coupling & drive plate as hard as I could,in an orderly fashion, without the use of a torque wrench. (I don't think the Travis Perkins ballast bag which got around the propeller & rudder the previous evening helped and may have even stressed the coupling causing it to work loose!)

 

I have marked the shaft and coupling to enable me to check the alignment and after 3 hours motoring there was probably a slight movement between shaft & coupling of about 2mm but this remained unchanged after a further 3 hours motoring.

 

My question is therefore what further measures can I take to ensure a better/permanent solution so this doesn't recur other than take the boat out of the water and put in a new shaft, et al, this early in the season. Would I be better fitting a new coupling immediately to replace the existing old one?

 

All help would be greatly appreciated

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Because of ill usage by either the previous owner or an over exuberant marine engineer, recently prop walking the boat, the drive shaft in our 52' narrow boat has worked loose on two previous occasions when others were using the boat. Worryingly it happen again to us whilst we were on the lower reaches of the River Soar approaching the Trent. Fortunately I had sufficient way to reach, just, the bank side and securely moor the boat.

 

The shaft had worked loose from the half coupling thus causing the bolts on both this and the drive plate to the gearbox to loosen. I slacked back all the nuts & bolts and this enabled me to push the shaft fully back into the coupling. In so doing I noticed that the coupling end of the shaft is badly scored. I then tightened the nuts & bolts of the coupling & drive plate as hard as I could,in an orderly fashion, without the use of a torque wrench. (I don't think the Travis Perkins ballast bag which got around the propeller & rudder the previous evening helped and may have even stressed the coupling causing it to work loose!)

 

I have marked the shaft and coupling to enable me to check the alignment and after 3 hours motoring there was probably a slight movement between shaft & coupling of about 2mm but this remained unchanged after a further 3 hours motoring.

 

My question is therefore what further measures can I take to ensure a better/permanent solution so this doesn't recur other than take the boat out of the water and put in a new shaft, et al, this early in the season. Would I be better fitting a new coupling immediately to replace the existing old one?

 

All help would be greatly appreciated

Mine did similar but remained tight after fitting with a torque wrench (I don't think the fitter had used one, or knew what one was.) I did post on here about it some time ago, and if my memory serves me correctly, some people grind a small flat on the shaft, then drill and tap a hole into the side of the coupling to form a pinch bolt onto the shaft. That is what I would have tried had it given further probs. Edited by Guest
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Because of ill usage by either the previous owner or an over exuberant marine engineer, recently prop walking the boat, the drive shaft in our 52' narrow boat has worked loose on two previous occasions when others were using the boat. Worryingly it happen again to us whilst we were on the lower reaches of the River Soar approaching the Trent. Fortunately I had sufficient way to reach, just, the bank side and securely moor the boat.

 

The shaft had worked loose from the half coupling thus causing the bolts on both this and the drive plate to the gearbox to loosen. I slacked back all the nuts & bolts and this enabled me to push the shaft fully back into the coupling. In so doing I noticed that the coupling end of the shaft is badly scored. I then tightened the nuts & bolts of the coupling & drive plate as hard as I could,in an orderly fashion, without the use of a torque wrench. (I don't think the Travis Perkins ballast bag which got around the propeller & rudder the previous evening helped and may have even stressed the coupling causing it to work loose!)

 

I have marked the shaft and coupling to enable me to check the alignment and after 3 hours motoring there was probably a slight movement between shaft & coupling of about 2mm but this remained unchanged after a further 3 hours motoring.

 

My question is therefore what further measures can I take to ensure a better/permanent solution so this doesn't recur other than take the boat out of the water and put in a new shaft, et al, this early in the season. Would I be better fitting a new coupling immediately to replace the existing old one?

 

All help would be greatly appreciated

I take it it is the split sleeve type of half coupling with two clamping nuts and bolts on either side, if so and the shaft has been turning in it it has probably worn both shaft end and the inner of the half coupling sleeve. There is often a locating screw on the upper side of those couplings with either a knurled end to grip the shaft or pointed which screws into a shallow drilled indent in the shaft. If there's wear like I said an application of Locktite 601 between the coupling and shaft will bond and jamb it tight (forever) although heat from a blowlamp will break it down for removal. Clean up shaft end and inner coupling sleeve with white spirit apply the Locktite liberally around the shaft, slip the coupling over TO THE EXACT position, tighten the four bolts and leave to cure for whatever it says on the bottle.

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I take it it is the split sleeve type of half coupling with two clamping nuts and bolts on either side, if so and the shaft has been turning in it it has probably worn both shaft end and the inner of the half coupling sleeve. There is often a locating screw on the upper side of those couplings with either a knurled end to grip the shaft or pointed which screws into a shallow drilled indent in the shaft. If there's wear like I said an application of Locktite 601 between the coupling and shaft will bond and jamb it tight (forever) although heat from a blowlamp will break it down for removal. Clean up shaft end and inner coupling sleeve with white spirit apply the Locktite liberally around the shaft, slip the coupling over TO THE EXACT position, tighten the four bolts and leave to cure for whatever it says on the bottle.

Wot he says.

 

CT

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Thanks guys for the suggestions & ideas, excellent and very much appreciated.

 

We're back to the marina tomorrow so I'll borrow a torque wrench and get some loctite for the best of both worlds.

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I'm guessing that the shaft is 1.5 inches dia, as a permanent fix just get the shaft turned down to something a bit less - 1.25 inches, 30mm or whatever then get a new half coupling to fit, you will need one anyway but at least you will save the cost of a shaft, however you will probably find that the above fixes will last for years.

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Yes, removing the shaft and turning it down is the correct engineering fix and it something I hope to do next winter but I'll use the previous suggested fixes to enjoy the season.

 

Again thank's for another excellent suggestion

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As an aside to this and for future reference; my previous boat had a half coupling which fitted onto a taper and locked with a keyway. Is this considered a better job? I am not very keen on the clamp on type.

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Again more positive and helpful suggestions, thank you. I think a 'friction fit' as in this case is possibly the least cost option in boat building terms and one which should be considered carefully, which I'll do if and when I buy my next boat!

 

Thanks for all your help.

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Some clamp type half couplings are slotted and keyed too, mine is but most don't seem to be. By turning down and reducing the shafts end diameter and fitting a clamp coupling to match will only reduce the clamping contact area which might induce it to slip more easily still.

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Yes, removing the shaft and turning it down is the correct engineering fix and it something I hope to do next winter but I'll use the previous suggested fixes to enjoy the season.

 

Again thank's for another excellent suggestion

 

As an engineer, I think you've got two options. You may be lucky and the shaft can be shortened - this is unlikely

 

In which case, you are looking at a new propshaft. Where are you going to find a coupling for a non standard, turned down shaft?

 

Richard

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Thanks, I can't fault your logic. It will be loctite for the summer then a re-build. Thanks again.

 

That's pretty much what I would do. If all else fails, the shaft and coupling are probably scrap anyway* so drilling and fitting a large roll pin would be a good temporary fix: http://www.ebay.co.uk/itm/ROLL-PINS-STEEL-SPRING-SELLOCK-PIN-VARIOUS-SIZES-/301164021759?var=&hash=item461ec647ff:m:m2ISOITio2NBkGdOXAfmAJQ

 

Richard

 

*shaft worn small, coupling worn large

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That's pretty much what I would do. If all else fails, the shaft and coupling are probably scrap anyway* so drilling and fitting a large roll pin would be a good temporary fix: http://www.ebay.co.uk/itm/ROLL-PINS-STEEL-SPRING-SELLOCK-PIN-VARIOUS-SIZES-/301164021759?var=&hash=item461ec647ff:m:m2ISOITio2NBkGdOXAfmAJQ

 

Richard

 

*shaft worn small, coupling worn large

What are your thoughts on drilling/reaming through and putting a tight fitting bolt through (parallel to pinch bolts) with a nut which would hopefully help tighten the clamp and stop the thing from slipping? 8 or 10 mm dia. maybe (30mm shaft)? (asking in case mine ever slips again!)

Edited by Guest
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What are your thoughts on drilling/reaming through and putting a tight fitting bolt through (parallel to pinch bolts) with a nut which would hopefully help tighten the clamp and stop the thing from slipping? 8 or 10 mm dia. maybe? (asking in case mine ever slips again!)

 

A roll pin would be easier. I doubt you could get a good enough surface for a bolt head to pull against. Plus, it's likely the bolt won't pull as tight as the four existing ones

 

Richard

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A roll pin would be easier. I doubt you could get a good enough surface for a bolt head to pull against. Plus, it's likely the bolt won't pull as tight as the four existing ones

 

Richard

Cheers :) What dia would you go for on a 30 mm shaft?

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OK - these are desperate measures and a terrible bodge. With that warning, I'd go for something around 8mm. That shouldn't weaken the shaft significantly and is still in the capacity of most electric drills

 

Richard

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OK - these are desperate measures and a terrible bodge. With that warning, I'd go for something around 8mm. That shouldn't weaken the shaft significantly and is still in the capacity of most electric drills

 

Richard

Cheers will pick one up and keep it for such desperate measures :) Well worth it for what it will cost. Some Locktie too for belt and braces approach.

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  • 1 month later...

To all those who provided advice, suggestions, solutions, here is an update. I replaced the coupling as suggested using the loctite and replacing with new nuts and bolts on both the flange and coupling. A day after the work was done we took the boat for a test run and the coupling failed almost immediately. A passing RCR guy suggested moving the shaft towards the stern to see if we could get a better fix on part of the unscored part of the shaft. That worked for a day then that failed above the River Trent below Fradley junction. RCR suggested a tow to a marina but Steve from Shobnall Marina came out and as a temporary measure inserted some makeshift shims to get a fixture. This got us going to Shobnall with a date for dry docking and a permanent fix.

 

Steve phoned on our way to the dock and said he had indentified the problem, which I and many more experienced missed. The Vetus shaft (which I didn't know I had) is 30mm but the coupling I had was a R&D and measured 1 ¼ inches!! A difference in diameter of about 0.03. No wonder it could never be fully tight! A lesson learnt by me.

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I assume the previous owner of the boat manage some cruising with it as the engine had done some 1300hrs. However the more the shaft was scored the harder it was to clamp it tight.

 

My failing, certainly inexperience, was not knowing the difference between Vetus & R&D standards. Imperial v metric in 2016.

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