How to tighten a prop nut.

[rogerthebodger]

It's clear that I'm definitely out-voted in my thinking that 100Nm should be ample for a castellated prop nut but until the OP comes back with a manufacturer's recommendation I guess that we won't get any further.

Richard

The tightening torque of a nut is more related to the tension exerted in the bolt/shaft in this case. This also is affected by the friction in the screw threads and the pitch of the thread.

The torque that a tapered coupling can transmit is related to the tension and more importantly the taper on the shaft.

In smallish power/torque drive systems a key ,either parallel or tapered key is much easier. It only when you get up to several thousand horsepower reversing drives that keyless taper drives become necessary due to stress concentration in the keyways and possible key fretting when the drive reverses.

 

[RichardS]

The tightening torque of a nut is more related to the tension exerted in the bolt/shaft in this case. This also is affected by the friction in the screw threads and the pitch of the thread.

The torque that a tapered coupling can transmit is related to the tension and more importantly the taper on the shaft.

In smallish power/torque drive systems a key ,either parallel or tapered key is much easier. It only when you get up to several thousand horsepower reversing drives that keyless taper drives become necessary due to stress concentration in the keyways and possible key fretting when the drive reverses.

So does that mean that you are now jumping ship and joining me in the "100Nm is ample for Graham's castellated prop nut" camp, Roger?

Richard

 

[rogerthebodger]

So does that mean that you are now jumping ship and joining me in the "100Nm is ample for Graham's castellated prop nut" camp, Roger?

Richard

I would need to do the calculations to determine what tightening torque is needed to ensure the taper drive friction/fit on the OP's boat is enough to drive the maximum output of the OP's engine.

To do this I would need more info and rack my brains (if I have any left) as last time I did this was over 35 years ago when I was in Engineering design in the UK.

Richard what engine is it that only has does not have a positive location between the camshaft and the camshaft pulley ?

 

[jamie N]

I realise that 'this' method can't be done in water, but on ROV thrusters without a keyway, and with a taper, we heat the prop boss, and slip it into place on the shaft, turn a non-nylok nut onto the shaft up to 'some' torque holding it in place, then we go away for a cup of coffee whilst the prop cools and then come back and replace the nut with a nylok. This works on a variety of thrusters, with a variety of power and with a very fast change of direction on the shaft.

 

[bikedaft]

random thought - if you provided 2 crates of beer on your foredeck and gathered enough passers by to stand there, can you get the prop out the water?? i really think it sounds too difficult without getting it above water. even with scuba kit? would help with power tools/not dying etc ;-)

 

[rogerthebodger]

I realise that 'this' method can't be done in water, but on ROV thrusters without a keyway, and with a taper, we heat the prop boss, and slip it into place on the shaft, turn a non-nylok nut onto the shaft up to 'some' torque holding it in place, then we go away for a cup of coffee whilst the prop cools and then come back and replace the nut with a nylok. This works on a variety of thrusters, with a variety of power and with a very fast change of direction on the shaft.

Shrink fits on drive is another way to increase the drive friction without using keys as you say when you have very quick direction reversals. ROV's have a relatively low power drive requirement like Richards camshaft drive.

 

[RichardS]

Richard what engine is it that only has does not have a positive location between the camshaft and the camshaft pulley ?

The Jaguar V8 engine (AJ26) introduced in 1996. As far as I know, even the current version of the same engine in the F Type still uses a tapered, keyless fitment.

Richard

 

[jamie N]

.....ROV's have a relatively low power drive requirement like Richards camshaft drive.

It's a sad world, that an SM8 has greater HP than my RC8D! And is more reliable..., and is easier to repair...., and has a ready supply of spares...., and so on....!
Bikedaft's suggestion meets every engineering protocol that I know off; lots of random personnel drinking beer and discussing the right way to achieve the objective, without actually contributing anything! :encouragement: I volunteer certainly.

 

[rogerthebodger]

The Jaguar V8 engine (AJ26) introduced in 1996. As far as I know, even the current version of the same engine in the F Type still uses a tapered, keyless fitment.

Richard

After my time

My Jaguar XJS has the ill fated V 12.

 

[rogerthebodger]

It's a sad world, that an SM8 has greater HP than my RC8D! And is more reliable..., and is easier to repair...., and has a ready supply of spares...., and so on....!
Bikedaft's suggestion meets every engineering protocol that I know off; lots of random personnel drinking beer and discussing the right way to achieve the objective, without actually contributing anything! :encouragement: I volunteer certainly.

Give any bunch of engineers the same problem and each will solve it in a different but acceptable way and still argue that their way is the only right way.

 

[jamie N]

Give any bunch of engineers the same problem and each will solve it in a different but acceptable way and still argue that their way is the only right way.

OMG, the hours of my life irretrievably wasted listening to rubbish, always ending with "I wouldn't have done it like that!"

 

[anoccasionalyachtsman]

random thought - if you provided 2 crates of beer on your foredeck and gathered enough passers by to stand there, can you get the prop out the water?? i really think it sounds too difficult without getting it above water. even with scuba kit? would help with power tools/not dying etc ;-)

First 35 in Cherbourg, worked a treat.

 

[Poignard]

First 35 in Cherbourg, worked a treat.

View attachment 76339

Followed by a few drinks in the cockpit. :encouragement:

Unfortunately these kind people were a bit on the light side and I got my sleeves wet.

 

[rogerthebodger]

First 35 in Cherbourg, worked a treat.

View attachment 76339

Have a look at post #19

 

[Graham_Wright]

Don't know your boat but could you do the old trick of heavy weights on the bow to lift the stern /prop out of the water then work from a dingy.

You in the sharpness dock. used to play along the river seven when I lived in the UK as my boat was moored for a time in Stourport.

A couple of problems;- no willing bodies around (in fact no bodies) and I doubt there would be sufficient room on the foredeck for sufficient bodies to lift the prop out of the water anyway! I could try winching down with the anchor.

 

[Poignard]

I could try winching down with the anchor.

You could, but when the anchor pulls free you will have a heavy boat dropping on your head.

 

[Yellow Ballad]

Apologies if it's already been suggested but could you not just use a tender and outboard to get you out of the canal and sail to somewhere to dry or crane out?

 

[rogerthebodger]

A couple of problems;- no willing bodies around (in fact no bodies) and I doubt there would be sufficient room on the foredeck for sufficient bodies to lift the prop out of the water anyway! I could try winching down with the anchor.

Being it winter I can understand that. Having been down to the wild fowl trust in summer lots of people then

 

[myquest]

I would just get back in the water with a windy gun, hold the shaft with one hand, shock the nut up tight and then until castelations lined up, split pin in, job done. Portable compressor, hose, windy gun, socket. I get the impression that you probably already have this sort of kit.

 

[Graham_Wright]

You could, but when the anchor pulls free you will have a heavy boat dropping on your head.

Ouch!

Could also pull a hole in the bed. Wouldn't be popular (but very dramatic!)