drive shaft

[sailorise]

I intend using a shortened lorry prop shaft and a standard thrust bearing to connect my 48hp 6cyl 1500rpm Lister with 2:1 reduction, to drive a shaft and 22"prop. The angle of the prop shaft is say, 5deg to the horizontal whilst the engine I'd prefer level. My question is, therefore; will there be a problem with the UJ on the g/box side running at a different angle to that on the thrust bearing side. Is it essential for them both to be running at the same angle ?

 

[hlb]

What worries me more, is where are you going to get a stern gland to fit your shaft. You can get a perpose made shaft for just over £100

 

[fisherman]

You might want to worry about the needle rollers in the U/Js, they won't like any sort of salt, but there may be a grease point: should you get aquadrive instead?

 

[sailorise]

Sorry, I wasn't clear enough. The prop shaft remains standard and terminates inboard into the thrust bearing. On the engine side of the thrust bearing is the first UJ operating at around 5deg. The other UJ (whose flange bolts onto the g/box output flange) operates at a slightly different angle. And my point is; does the inevitable 'out of tune' rotational speeds have any noticable effect in practice.
I'm not seeking theoretical answers - they are well documented - but someone who has had similar situation to overcome.
The aquadrive solution is too expensive for my taste. A heavy duty lorry prop shaft costs me £5 and a thrust bearing not much more.

 

[pheran]

[ QUOTE ]
A heavy duty lorry prop shaft costs me £5 ....................

[/ QUOTE ]
With knackered U/Js presumably? Have you factored these into your costs?

 

[spannerman]

Its better if the prop shaft runs as true as poss, is it not possible to mount the engine at an incline, many boats have engines mounted on an incline or that when in operation aren't completely horizontal, especially semi displacement types. Just check that the oil pickup in the sump will remain submerged if its at the front of the engine, it may req a little extra oil in the sump.

 

[andrewbarker]

IMHO you need 2 UJs per shaft - 1 each end - to equalise the acceleration/deceleration forces. Then the UJs will always be at the same angles.

Or.... could you get away with a shaft with a single CV joint? For your HP that shouldn't be a prob.

 

[fisherman]

A carden shaft may be a better option, google it, and try Fenner transmission products.

 

[ipw]

Hi if you get the welding wrong and it is out of balance you may wreck your boat. Try your local propshaft guy or try these which i use all the time.... jon@dandfltd.co.uk

 

[ipw]

sorry thats his e mail the web site is www.propshafts.co.uk

 

[sailorise]

Thanks everyone for your advice, I've followed thro on each one and now have the answer clear in my mind.
Just thought I'd mention to Pheran; I've never found lorry UJs to be anything other than in excellent condition - regular servicing - but not so with domestic vehicles.
Spannerman; The Lister will run at 6.5deg but is limited by the sump/bilge timbers.
fisherman; I agree. I live on the beach and know how destructive salt is. However, UJ bearings are cheap.
Ipw; easier to get the line up right, than wrong. And its only 500rpm anyway. I liked your site.

Thanks again