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Old 11 January 2015, 14:40   #1
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Flexible coupling

Sorry, this isn't RIB related, but I'm sure there will be people on here with an opinion.

The little project I'm working on at the moment involves a small inboard engine and shaft drive prop.

I've never had the engine fitted to the boat so have no original fittings.

I've sourced some aluminium to machine up a flexible coupling, and will be aligning the engine output shaft and prop shaft really well.

However today when looking at it I had a thought.

The propshaft and engine output shaft are only 5/8in in diameter.
The engine itself is very low power and torque, a 4.5HP 2-stroke, and it will drive a small 8x7 prop.

So the thought occurred, that considering the low torque/HP, and the good alignment I'll achieve, why don't I just join the two shafts with a length of thick wall rubber hose pushed over and clamped to each shaft with a small gap between the shafts inside the hose.

What do you think?
Would it last very long?
Am I being daft?

Nasher.
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Old 11 January 2015, 18:11   #2
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No, not daft.
I'd have some form of flexi coupling in there if I could. Hose or a rubber doughnut would be my first go-to.
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Old 11 January 2015, 18:31   #3
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A steering column uj from a breakers yard should work fine just need to find one roughly the right size & maybe bore out the splines but at 5/8 dia you should be in the right ball park might be more robust than a hose & clips
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Old 12 January 2015, 04:18   #4
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Nasher, I thought drive shafts were offset slightly to make the UJ joint work properly as a joint. If they are in a straight line it causes problems with wear and vibration.

A steering UJ is a good idea and would look like a proper bit of engineering. Have to be a landie one though
Pete
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Old 12 January 2015, 07:31   #5
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Quote:
Originally Posted by Pete7 View Post
A steering UJ is a good idea and would look like a proper bit of engineering. Have to be a landie one though
Pete
Pete Hi.

Yep, good idea by Beamishken, I'm thinking of:
NTC3486 Genuine Land Rover Range Rover Flexible Steering Coupling | eBay

As far as I'm aware a UJ(Universal Joint) needs to be slightly at an angle, but a CV Joint(Constant velocity Joint) can work straight.
Might have that the wrong war round though.

Nasher.
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Old 25 January 2015, 13:15   #6
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Been thinking about this some more today having managed to get a couple of hours to myself.

The ideal solution appears to be a rubber doughnut type coupling exactly like the Hillman imp one hanging on my garage wall, but unfortunately it's too large in diameter.

Thinking about Beamishken/Pete7s suggestion, it appears Range Rovers have a similar thing in their steering column, but I'm not sure how it would stand up to constant rotation.
See Imp one and RR Steering one below.

So a question for those of you who've played with different types of Cars, Bikes etc over the years - What's the smallest Rubber Doughnut type coupling you've come across?

Nos4r2, I'm expecting you to mention the Ural one

Nasher.
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Old 25 January 2015, 17:52   #7
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Never owned a Urinal.

I wonder... there's a rubber cush drive in one of the old GS wheels I have lying around.
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Old 26 January 2015, 07:51   #8
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Hose.

Multispiral Hydraulic hose will do the job really well, especially if use 2 bolt type band clamps each end 180 degrees rotated to keep it in balance.
a piece of hose will allow slight radial and axial miss alignment and is actually a really good constant velocity joint.
a Hooke type UJ will only allow axial miss alignment and not radial, and then it will vibrate as its nor a constant velocity joint. If you have a UJ driving through an angle (like a prop shaft on a car) you need two at equal angles with the yolks rotated 90 degrees to end up with constant velocity at the output.
Rag joints are quite forgiving and there's some smallish ones on Daihatsu and Toyota steering columns and land rover slightly larger as you already know. I have some small Ujs but at 1/4 inch shaft too small I think.
you probably already thought of this but most joints will not take any thrust without vibrating badly or breaking.
personally I would try hydraulic hose(we use it in work on an automotive dynamometer 2" and it lasts!!) or landrover steering UJs (cheap and plentiful)
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Old 27 January 2015, 09:21   #9
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Thanks Nos and Doggy.

Think I'll get hold of a Rangie one as above to see what it's like, but really like the idea of the simple bit of hose.

I'll try to get a piece of what you suggest in a @5/8'ID, double up the clamps and spread them around for balance, and put a spare bit in the boat just in case.
Or if I can only get larger I'll machine up some sleeves for the shafts.

It will be a while before it's ready to go anyway.

Nasher.
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Old 27 January 2015, 09:31   #10
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Country: Other
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Thought I'd put some pictures up of what I'm up to.

1940's Mk9 Military canoe that I've owned for 30yrs, and while it's been at the National Maritime Museum in Falmouth for a few years I've sourced the correct engine. It's believed to be the last Mk9 around.
There is a book on the whole series developed from the Mk1 Cockleshell Heroes Canoes.
The guy who wrote the book on them used mine for a lot of reference photos.
http://www.amazon.co.uk/The-Cocklesh.../dp/1848680651

Images 1, 2 and 3 are the boat itself. Image 3 is obviously a historic image from the NMM Archives.
Image 4 is a historic image of the engine in the boat.
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