Propellor Nut (Castellated) Torque Setting

[Deleted member 36384]

Hello,
I have a 38 mm nut to hold my propellor on. When I took it off it was very, very hard to get started with a 24" bar and several smacks with a 2 lb hammer to get it moving. I have no idea if lock tight had been used but there was a compacted white powder on the threads that looked like barnacle shell dust! The nut could not be released by hand and the 24" bar was used all the way with a lot of effort (but no hammer) until the last few threads. The propellor shaft is stainless and the nut a brass or bronze material. I'll lightly grease the thread and taper and of course its all been cleaned up.
What do you think for the torque - the weight of one man on the end of the bar, smacking the nut up tight with the 2 lb lump hammer or something more scientific; I have a torque wench.
Thanks,
BlowingOldBoots

 

[RichardS]

If there is no manufacturers specification, I would just do it up tight since it is impossible for it to come undone. Something like 50Nm and then back to the next castellation would be fine.

Others will have different opinions.

Richard

 

[pvb]

Assuming there's a keyway on the shaft, I'd tighten it to 50-100Nm. It might help you to mark the end of the shaft with the orientation of the split pin hole.

 

[Deleted member 36384]

Great stuff! I'll take it to +50N and the next hole for the split pin. Yes there is a keyway.
Thanks to both of you for the quick response.

 

[VicS]

If there is no manufacturers specification, I would just do it up tight since it is impossible for it to come undone. Something like 50Nm and then back to the next castellation would be fine.

Others will have different opinions.

Richard

Assuming there's a keyway on the shaft, I'd tighten it to 50-100Nm. It might help you to mark the end of the shaft with the orientation of the split pin hole.

Can I ask where you found these figures or arrived at them

They are significantly greater than I was finding in any tables

I assume BOB means a nut 38mm across the flats , which I think would probably indicate a 1" diameter thread. BSW. BSF or possibly UNC or UNF

 

[Lucy52]

As a ball park figure Darglow recommend 45lb ft for the securing nut on a Featherstream propeller.

 

[Mistroma]

Figures sound about right. My prop. nut was very tight first time it was removed but I think that was more due to growth on the threads (I also had compacted white powder on the threads). I marked the shaft with tape and location of castellation with pin wrt the shaft. I think I tightened to about 45-50 ft-lbs to get the holes back into what seemed to be the original alignment. Slackening off one turn would have been way too loose and another full turn would have been impossibly tight.

I can't remember the exact torque when it was aligned as it was quite a while ago but the figures mentioned are in the region I was aiming for. I also counted the turns used to remove the nut so I'd be happy that the prop was fully home when tightening (so no burrs or grit inside) if approx. same turns when assembling.

I also didn't tighten in one go and let it rest for 10-20 mins. before finishing in case any lubricant squeezed out even though I'd used the lightest spray and mostly wiped it off.

Obviously brain fade when I posted, as I had forgotten my previous boat had a castellated nut and current one has a tabbed washer. Same principle though and I just repeated the procedure last time but aligned to the already bent part of washer instead of a hole.

 

[LadyInBed]

When I did mine, no torque wrench to hand, I tie a length of wood to the prop blades to stop them turning then tighten the nut as tight as I could with a standard length tommy bar, then backed the nut off (loosen it) until it lines up with the hole in the prop to put the split pin through.

 

[sailaboutvic]

This also depend on where the nut ends up with the split pin holds .
Even if it was just done up by hand not using any leverage it's not going to come undone unless the pin fall out .

 

[Skylark]

My Flex o Fold with M22 AF non ferrous nut on a stainless steel shaft is 90Nm dry. Threadlock is not recommended. Lubricating the thread reduces torque by a factor of 0.8. I always use a torque wrench to assemble the prop at the start of the season. This design uses a tab washer for additional retention security.

 

[AndrewB]

I agree with the above advice, but even if the nut can't come off you still need it tight. A problem with a castellated nut that must take up one of six positions - one position may be too tight, but the previous one slightly loose. I keep a few large washers of different thicknesses that can be optionally inserted each time the propeller is refitted, and choose the combination which gives the tightest fit. (This did vary from year to year at first, though now its always the same washer).

 

[RichardS]

Can I ask where you found these figures or arrived at them

They are significantly greater than I was finding in any tables

I assume BOB means a nut 38mm across the flats , which I think would probably indicate a 1" diameter thread. BSW. BSF or possibly UNC or UNF

I can't speak for PVB but in my case it's just multiple decades of experience with spanners.

Richard

 

[Stemar]

Whatever torque you use, I'd grease the threads well, or it'll need a lot more torque - and a fair bit of shouting - to get it off next time.

 

[Deleted member 478]

Is shouting better than torquing?

 

[Graham376]

As a ball park figure Darglow recommend 45lb ft for the securing nut on a Featherstream propeller.

+1

Just refitted mine an hour ago but it uses Nord-lock washers rather than castellated nut and split pin, which may make a difference to torque.

 

[Norman_E]

If there is no manufacturers specification, I would just do it up tight since it is impossible for it to come undone. Something like 50Nm and then back to the next castellation would be fine.

Others will have different opinions.

Richard

It depends on thread diameter and pitch but 50nm or about 75 ft lb would be OK if the thread diameter is around 5/8th inch. All the nut has to do is ensure that the propeller is securely fitted to the shaft taper, and accurate machining of both tapers is far more important than nut torque. No amount of torque will compensate for a badly fitted taper. My recommendation for a 5/8 inch or 16mm thread is do it up to 50nm, and see if the split pin will go in. If it won't apply a bit more torque until the pin can be inserted. The chances are that the thread is fine relative to diameter and the extra turn will require little more torque. I do not favour turning the nut back to line up the hole and extra tourque within reason will do no harm. 16mm wheel nuts are sometimes recommended to be torqued as high at 180nm! They are high tensile steel, not relatively soft stainless but even with the latter you could safely go quite a bit above 50nm. I would not apply any thread locking adhesive, but would always use a new split pin, choosing one that is a close fit in the hole.

 

[VicS]

It depends on thread diameter and pitch but 50nm or about 75 ft lb would be OK if the thread diameter is around 5/8th inch. All the nut has to do is ensure that the propeller is securely fitted to the shaft taper, and accurate machining of both tapers is far more important than nut torque. No amount of torque will compensate for a badly fitted taper. My recommendation for a 5/8 inch or 16mm thread is do it up to 50nm, and see if the split pin will go in. If it won't apply a bit more torque until the pin can be inserted. The chances are that the thread is fine relative to diameter and the extra turn will require little more torque. I do not favour turning the nut back to line up the hole and extra tourque within reason will do no harm. 16mm wheel nuts are sometimes recommended to be torqued as high at 180nm! They are high tensile steel, not relatively soft stainless but even with the latter you could safely go quite a bit above 50nm. I would not apply any thread locking adhesive, but would always use a new split pin, choosing one that is a close fit in the hole.

The OP says the nut is 38 mm
I assume he does not mean that it has an M38 thread but rather that it is 38mm across flats. The nearest threads that would correspond to this are , as I said earlier, 1" BSW, BSF, UNC or UNF. Somewhat larger than the 5/8" you are considering.

Also he says that the nut is bronze or brass, not "high tensile steel" or even " relatively soft stainless steel"

 

[zoidberg]

The 1" shaft on my ould Cutlass came without an 'ole for a split pin. There was a Nyloc nut, which is due for replacement when the prop comes off for burnishing and 'pimping' with some prop-paint.

In conversation a surveyor remarked it would be OK to use a fresh Nylok nut with a twin- tab washer. Others here reckon I should drill an 'ole in the shaft-tail and fit a splitpin anyway.

What does the team think?

 

[Norman_E]

The OP says the nut is 38 mm
I assume he does not mean that it has an M38 thread but rather that it is 38mm across flats. The nearest threads that would correspond to this are , as I said earlier, 1" BSW, BSF, UNC or UNF. Somewhat larger than the 5/8" you are considering.

Also he says that the nut is bronze or brass, not "high tensile steel" or even " relatively soft stainless steel"

If the thread is 1 inch then the torque I specified will still be enough to hold a well fitted taper, and well within the tolerance of a brass nut but I would not assume that the nut is a standard size as a propeller nut could well be a one-off rather than a standard nut.

P.S. If the OP specifies the thread diameter and pitch we can probably calculate the maximum safe torque, which will be far greater than what is needed to retain the propeller, particularly if it has a key as well as a taper fitting.

 

[Poignard]

The 1" shaft on my ould Cutlass came without an 'ole for a split pin. There was a Nyloc nut, which is due for replacement when the prop comes off for burnishing and 'pimping' with some prop-paint.

In conversation a surveyor remarked it would be OK to use a fresh Nylok nut with a twin- tab washer. Others here reckon I should drill an 'ole in the shaft-tail and fit a splitpin anyway.

What does the team think?

I had a new propshaft made by T.Norris Ltd and when I went to collect it it had a Nyloc nut instead of a castellated nut. I got them to drill for a split pin and fit a castellated nut. Not because I didn't trust a Nyloc, which of course I do, but because I would have had to carry a spare since I would not re-use a Nyloc nut if I had to take the prop off for any reason, whereas split pins are cheap and readily available and I always have an assortment on board.