How to tighten a prop nut.

SAPurdie said:
I'd lay odds that the earlier poster suggesting that you had a woodruff key which has split longitudinally is indeed the case. The chance of securing a prop against the several Nm developed by your engine using just a taper and nut, still less a castellated nut with split pin, is pretty small.

If you can find and replace the key, which will be well smeared over by the prop rotation, then the nut torque needed to limp somewhere for a lift out need not be that great.
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It’s perfectly good engineering practice not to use a key with a taper and no key is most likely better than a badly fitting one that disturbs the taper fitting.
But the clue would be lack of key way in the prop which would be seen from boss end .
But in practice 95% will have a key so you may be right.

Thinking further trying to fit a new key properly under water makes tightening the nut look simple
 
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SAPurdie said:
I'd lay odds that the earlier poster suggesting that you had a woodruff key which has split longitudinally is indeed the case. The chance of securing a prop against the several Nm developed by your engine using just a taper and nut, still less a castellated nut with split pin, is pretty small.

If you can find and replace the key, which will be well smeared over by the prop rotation, then the nut torque needed to limp somewhere for a lift out need not be that great.
Click to expand...

No key. Big ship style. There was an extensive post a while ago comparing with and without.

From time to time I have repaired or remanufactured macerator shafts for the chicken processing factory opposite. (The smell is sickening!). When (in this case) a pulley or gear overcomes a key, the shaft is generally beyond repair. It also can make removing said pulley or gear practically impossible. This is 316 on 316 so galling rears its head.

The weather is not fit for diving today - storm forecast so the excitement will have to wait!
 
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I am quite surprised there is no key/keyway on your prop/shaft.

Most keyless couplings are on very high power/torque drives where a keyway would introduce a week point/stress raser stress concentration that would introduce fatigue failure.

Big commercial shipping do have this arrangement but the prop is fitted with the aid if hydraulic pressure with a shallow taper.

https://www.google.co.za/search?q=k...b3YAJgQtI8BKAB6BAgBECI&biw=1366&bih=625&dpr=1
 
Graham_Wright said:
I agree. My source was;-
https://www.fastenal.com/content/feds/pdf/Torque of Metric Stainless Steel.pdf.

I can't imagine I can approach that. I also can't imagine it is necessary for this application.
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What did you torque it to when you fitted the prop? Those figures in the table are for regular bolts/studs like the M22 wheelnut I mentioned, albeit stainless. I'm no engineer but I can't imagine they apply for a bronze(?) prop on a taper. Depending on the size of the boss I would have thought you could crack the casting and I hate to think how you'd get it off again! :-)

If it is correct trying to do it underwater doesn't seem like a very good idea!
 
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Graham_Wright said:
I agree. My source was;-
https://www.fastenal.com/content/feds/pdf/Torque of Metric Stainless Steel.pdf.

I can't imagine I can approach that. I also can't imagine it is necessary for this application.
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I think my surprise was misplaced. That's right for a 22mm coarse thread. (2.5 mm pitch).

I've made an awful lot of assumptions based on your shaft diameter being 32mm (which, from what you allude to there, is about right) - taper, boss length and cross section and calculate that 500N wouldn't do any damage to a bronze prop.

Not torquing it to that would risk the nut coming loose (and you shouldn't rely on the split pin for that).

Apologies for the misguided interruption....
 
I would have if it was out of the water, bit suspect it could be deafening if used under water, they are noisy.
 
Graham_Wright said:
I steer a good reason nobody suggested this ;-
https://www.ebay.co.uk/itm/KS-Tools...101323&hash=item340597aeea:g:Lz4AAOSw7Khce6yy
?

I could possible hire one but the air supply might be tricky. 100 psi is, I think, the first stage pressure from my dive tank.

An alternative might be a cordless one.

Perhaps I could hire one or the other? (No need to mention they would be used underwater:nonchalance:)
Click to expand...

I have one in my workshop, but the rule is that they're never used to tighten, the torque isn't predictable.
 
My 300bhp V8 Jaguar has a simple taper on the four overhead cam shaft pulleys. There are no woodruff keys. The nut which secures the pulley on the taper is only tightened to 100Nm. Bearing in mind the forces being transmitted against those 8 valve springs, I'm not sure why a propellor would need to be any tighter.

Richard
 
RichardS said:
My 300bhp V8 Jaguar has a simple taper on the four overhead cam shaft pulleys. There are no woodruff keys. The nut which secures the pulley on the taper is only tightened to 100Nm. Bearing in mind the forces being transmitted against those 8 valve springs, I'm not sure why a propellor would need to be any tighter.

Richard
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The nut torque value does depend on the angle of the taper, dia and length of the shaft/pulley together with the maximum drive torque.
 
RichardS said:
My 300bhp V8 Jaguar has a simple taper on the four overhead cam shaft pulleys. There are no woodruff keys. The nut which secures the pulley on the taper is only tightened to 100Nm. Bearing in mind the forces being transmitted against those 8 valve springs, I'm not sure why a propellor would need to be any tighter.

Richard
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The higher axial force pushing the prop on is really just a by-product of using the correct torque for the thread size (I believe it's 22mm in this case). If the threads aren't stretched enough the nut can rattle off.

What's the thread size on your camshafts? M10 or M12?
 
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anoccasionalyachtsman said:
The higher axial force pushing the prop on is really just a by-product of using the correct torque for the thread size (I believe it's 22mm in this case). If the threads aren't stretched enough the nut can rattle off.

What's the thread size on your camshafts? M10 or M12?
Click to expand...

I can't remember the thread size on the cams but it's probably more like 15mm.

However, I believe that the prop nut has a split pin so it's never going to come off. I should also point out that the torque setting for a particular nut is related to the job it has to do and not to the thread diameter per se. The thread diameter and pitch only governs the maximum torque for a particular material.

I was tightening up some massive nuts on a car hub recently, something like 30mm thread and the torque required was something like 5Nm because that is all the application requires. :)

Richard
 
Rogershaw said:
The nut torque value does depend on the angle of the taper, dia and length of the shaft/pulley together with the maximum drive torque.
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Indeed so .... but ignoring all other factors, compared to the force required to turn a camshaft in a 32 valve high-performance motor, how much torque do you think is required to turn a prop in water?

I would be amazed if more than 100Nm is required. :)

Richard
 
RichardS said:
Indeed so .... but ignoring all other factors, compared to the force required to turn a camshaft in a 32 valve high-performance motor, how much torque do you think is required to turn a prop in water?

I would be amazed if more than 100Nm is required. :)

Richard
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Depends on the maximum torque output of the engine and gearbox reduction ratio assuming the prop is matched to the engine and gearbox ratio.

My perkins max torque is about 250-270 Nm @ 1400 rpm times 2 for gear ratio.
 
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RichardS said:
Indeed so .... but ignoring all other factors, compared to the force required to turn a camshaft in a 32 valve high-performance motor, how much torque do you think is required to turn a prop in water?

I would be amazed if more than 100Nm is required. :)

Richard
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Engine losses analysis is a first year engineering lab but I've chucked my notes away and went for Google. This is pretty good on the friction.

https://link.springer.com/content/pdf/10.1007/s40544-016-0107-9.pdf

Your one camshaft could be using as much as 1.7hp, and maybe 2.5Nm.

And as Roger says above, the prop's going to take a lot more than that.
 
Your camshaft is not likely to run astern with the pulley experiencing a thrust pulling it off the shaft.
Its also unlikely to be hit by a semi submerged log..
 
Rogershaw said:
Depends on the maximum torque output of the engine and gearbox reduction ratio assuming the prop is matched to the engine and gearbox ratio.

My perkins max torque is about 250-270 Nm @ 1400 rpm times 2 for gear ratio.
Click to expand...

anoccasionalyachtsman said:
Engine losses analysis is a first year engineering lab but I've chucked my notes away and went for Google. This is pretty good on the friction.

https://link.springer.com/content/pdf/10.1007/s40544-016-0107-9.pdf

Your one camshaft could be using as much as 1.7hp, and maybe 2.5Nm.

And as Roger says above, the prop's going to take a lot more than that.
Click to expand...

NorthUp said:
Your camshaft is not likely to run astern with the pulley experiencing a thrust pulling it off the shaft.
Its also unlikely to be hit by a semi submerged log..
Click to expand...

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
 
https://www.pbase.com/mainecruising/fitting_a_prop
http://highseasyachtservice.com/2011/03/lapping-propellers-to-shaft/
https://www.ashleyriverboatworks.com/lapping-the-prop-to-the-shaft/

A few hints on lapping. Why two nuts? I understood locking nuts have a questionable purpose.

Now to find some underwater lapping paste. Some are water based, some oil. I guess the latter has a better chance.

To find the split pin hole, I thought of securing a jubilee clip on the shaft end with a mark in line with the hole.
 
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