Prop shaft nuts

[zoidberg]

Among the many jobs, once I remount the prop, I'll need to replace the prop shaft nut..... but what with?

First, it's presently 3/4" Nyloc, and I have several of them, spares. Would it be adequate to stick with a fresh Nyloc nut; should I provide additional security; should I convert to a plain nut....

I can fit a tab washer, and will do so. Ought I to find a way to drill through the nut, tap it, and insert a locking grub screw? Or would application of 'The Right Grade Of Loctite' suffice?

• Red: High strength, permanent adhesion
  • Select for high vibration applications where the components don’t need to be disassembled in the future.
• Green: High strength wicking, permanent adhesion
  • Select for high vibration applications for preassembled fasteners that don’t need to be disassembled in the future.
• Blue: Medium strength, removable with torque
  • Select to ensure components don’t come loose in the application and there is a possibility of disassembling the components in the future.
• Purple: Low strength, easily removable
  • Select for non-crucial applications and if disassemble of the components in the future is a known possibility.

 

[MikeCC]

You could look at Heico washers. Other brands doing the same job available. They are two washers with cams facing each other. If the secured item starts backing out, the cams wedge apart to oppose it.

 

[Tranona]

Nyloc and tab washer is already overkill. Tab washer on its own with a plain nut is sufficient. Remember the nut is already only there as a back up to the taper. You find this out when you try to remove a prop.

 

[jamie N]

Are there any prop manufacturers that recommend heating the prop prior to fitting onto the taper?
One well known ROV manufacturer has this as standard procedure, but in my limited experience, I've never heard of it on a yacht.

 

[jwfrary]

Are there any prop manufacturers that recommend heating the prop prior to fitting onto the taper?
One well known ROV manufacturer has this as standard procedure, but in my limited experience, I've never heard of it on a yacht.

I warm them a little, not much and lubricate the prop nut wang it up as tight as I can. Leave it 24hrs then take the nut off, clean the thread with degreaser and dry. Then use liquid blue locktite and a tab washer.

These are on fairly big props 40 inches or so. But the same principles apply. Don't use green or red as you'll need a lot of heat to get the nut off again.

Most of the old school setups use a double nut with a castellasted nut and pin. I don't use locktite on those. Just when relying on a tab washer.

 

[Plum]

Nyloc and tab washer is already overkill. Tab washer on its own with a plain nut is sufficient. Remember the nut is already only there as a back up to the taper. You find this out when you try to remove a prop.

agree, tab washer is a good method. It does, of course need to engage in the keyway too with this type Propeller shaft tab washer in stainless steel. 50mm diameter to suit M24 thread | eBay but in true PBO fashion you just need a plain 1mm thick large diameter washer and make your own saw cuts.

www.solocoastalsailing.co.uk

 

[rotrax]

Fitting tapered flywheels, clutches and canwheels to motorcycles was a big part of my working career.

No secrets, it is easy. But, certain things must be in order. If they are not, disaster is around the corner.

If we get back to props and propellers, my method is as follows:-

Ensure both the taper in the prop and the taper on the shaft are clean and smooth. At this stage I do no grinding or blueing, it might not be needed.

I put the prop onto the shaft without the key, pressing it hard onto the taper. Then, using a block of wood, tap the prop boss until it is fully in place, does not move up the shaft any further.

The shaft then has a turn of tape put around it at the forward edge of the boss. This marks how far the prop must go on to be secure. The prop is now removed - often requiring use of a puller - that is good!

Next, I put the key in place, and refit the prop, using the wood block as before. It is very important that the forward edge of the prop boss reaches the marker tape EXACTLY!

If it does not, the prop is keybound. The key must be reduced in height by grinding or filing until the prop goes on up to the tape marker again EXACTLY!

The key is purely a locator, not a drive link. The tightly fitting taper transmits the drive. Many high torque drives have no key, just a taper. Unless required for timing or balance, a key serves no purpose.

Once the key is pronounced good the prop can be fitted.

If when trial fitting the prop does not need a tap or a puller to remove it, grinding of the tapers might be required using grinding paste. Once even dull grey and dull bronze surfaces are made, clean perfectly with solvent and try another trial fit. The prop should be pushed and tapped into place with the wood block and should not just pull off. Even with no nuts on, the taper should be tight, requiring a tap or a puller to remove the prop.

When tightening I use a length of timber at a prop blade root to the ground to stop the shaft rotating while tightening to the reccomended torque.

As for locking devices, my chosen vessel has a double nut arrangement, the outer nut drilled right through the shaft for a cotter pin. 0ne and a quarter inch shaft, big prop, always lines up perfectly.

My prop is a 21 x 17 IIRC and has a big torque figure when tightening.

 

[oldgit]

"As for locking devices, my chosen vessel has a double nut arrangement, the outer nut drilled right through the shaft for a cotter pin. 0ne and a quarter inch shaft, big prop, always lines up perfectly."

Stainless Nyloc Nut and stainless Tab washer.
Far less faff.

 

[Daydream believer]

Double nut -if room for 2-& drill & pin the outer one. Once the hole is drilled it should be there forever, unless the tapers were not cleaned & fitted properly in the first place.
Would rather use a castelated nut if available

 

[Malish]

Back to the OP - has your current arrangement ever caused problems? If not then why change?

 

[zoidberg]

Back to the OP - has your current arrangement ever caused problems? If not then why change?

It's an Ould Boat I'm refurbing. Many features and items 'as found' were sub-optimal or plain inadequate. I'm looking hard at every component, from through-hulls to mast wiring. The simple device that holds the prop in place needs to be fail-safe; otherwise, the prop may go walkabout at an inconvenient moment.

I'm very aware that exactly that happened to a friend's trimaran during the pre-start of the 2003 Fastnet Race off Cowes. An £800 folding prop popped off in an extremely busy small patch of sea. After a minute or three's consternation, he continued to race.... to Ireland and back. He shouldn't have done.
A lesson learned - by me, at least.

 

[rotrax]

Double nut -if room for 2-& drill & pin the outer one. Once the hole is drilled it should be there forever, unless the tapers were not cleaned & fitted properly in the first place.
Would rather use a castelated nut if available

I agree.

Island Packet do fit the prop correctly, my second nut ALWAYS lines up with the cotter pin hole.

 

[Graham_Wright]

The key is purely a locator, not a drive link. The tightly fitting taper transmits the drive. Many high torque drives have no key, just a taper. Unless required for timing or balance, a key serves no purpose.

Interesting. What does it locate and why? Is it for in-situ balancing?
There is no key on mine.
I was put off by having to repair customers' shafts where the key had worn and the shaft rattled causing the key to jam in its housing.

 

[doug748]

I would attend to Post 2 - provided you have the keyway, it's a winner.

 

[Moodysailor]

There is a little bit of misunderstanding about the role of tapers & keyways in this context on this thread - some of the information is correct in theory but misapplied, and some is a little bit misunderstood.

In answer to the OP, go with tried & tested approaches for prop nuts - a physical lock using a (new) tab washer, castle nut & cotter pin or double nut & cotter pin. I would not advise a nyloc not or thread locker for a prop shaft nut.

 

[Daydream believer]

As I understand it a tab washer bends 2 ways. One way it bends over the superstructure against which the item is being bolted whilst the other bends over the nut. That prevents nut rotation== YES_NO?
If that is correct- i may be wrong so my next assumption ( & we all know what assumption is ) could be wrong as well. It stands to reason that if the backing structure is rigid, ie a framework , then all is Ok. However, if the backing structure is a moveable item, ie a prop with no keyway on a tapered shaft then the backing structure can move.
In that case the prop can rotate ( Poor fit, Vibration causing wear etc) & take the nut with it. Tab or no tab. On top of that it would have to be a jolly big washer to be big enough for the tab to not only bend over the nut, but the boss of the prop as well.
Seems to me a tab washer that did not do both is pointless & all the "tab washer whallas" are talking b..x. But then I might be so I have to be careful
So keeping my head down to avoid having it blown off , can those who know about those things please put me right-Because I am not saying either way, only applying a bit of logic to lack of knowledge & that can be dangerous. But I might be right of course
By the way i have a Brunton Auto prop & their fastening system is rather clever

 

[Moodysailor]

As I understand it a tab washer bends 2 ways. One way it bends over the superstructure against which the item is being bolted whilst the other bends over the nut. That prevents nut rotation== YES_NO?
If that is correct- i may be wrong so my next assumption ( & we all know what assumption is ) could be wrong as well. It stands to reason that if the backing structure is rigid, ie a framework , then all is Ok. However, if the backing structure is a moveable item, ie a prop with no keyway on a tapered shaft then the backing structure can move.
In that case the prop can rotate ( Poor fit, Vibration causing wear etc) & take the nut with it. Tab or no tab. On top of that it would have to be a jolly big washer to be big enough for the tab to not only bend over the nut, but the boss of the prop as well.
Seems to me a tab washer that did not do both is pointless
So keeping my head down to avoid having it blown off , can those who know about those things please put me right-Because I am not saying either way, only applying a bit of logic to lack of knowledge & that can be dangerous. But I might be right of course

You are correct, one part of the tab would go into the keyway, the other would be bent over the flat on the nut. If there is no way to prevent rotation of the prop on the shaft then there is nothing to lock the nut either.

 

[Graham_Wright]

I would attend to Post 2 - provided you have the keyway, it's a winner.

Er?
I (used to) provide a service to a local chicken processor.
Sometimes, a macerator shaft for instance, would be presented to me to copy. The key had graunched both shaft and whatever it was driving beyond repair!

I use a castellated nut on my prop shaft with a split pin through the shaft.

 

[rotrax]

Interesting. What does it locate and why? Is it for in-situ balancing?
There is no key on mine.
I was put off by having to repair customers' shafts where the key had worn and the shaft rattled causing the key to jam in its housing.

I believe it is almost tradition, most props and shafts have a key, so we expect them.

In your post above, that sounds exactly what I warned against, the props bound on the keys, not the taper.

Aermacchi racing motorcycle engines had the crankshaft pinion held by a plain taper, no key. When the clever Itallian bugger Linto made two 250's into a Grand Prix 500 by making a new bottom end and using two 250 heads and cylinders he kept the plain taper which was trouble free with double the power. Getting the crank pinion off an Aermacchi engine was a real performance they were so tight on the taper!

A test for a 1930's Speedway mechanic was fitting the outside flywheel to a racing Douglas twin. As a well ridden one often had the outside flywheel dragging in the cinders and hitting the track - making a big shower of sparks while it did so -keeping one on the engine was a prime requirement. Flywheels were often seen whizzing down the track on their own! No key on a Douglas Dirt Track engine flywheel either.

Most motorcycle flywheel magneto's are on a keyway and taper. This ensures the points cam or trigger in a CDI system is located correctly. Many an engine has been wrecked by poor fitting/keybound taper. This can make the shaft look like a Walnut Whip - remember them?

The early Reliant three wheel cars had a long slow taper holding the rear hubs onto the half shafts. No keyway or key. We used an expensive hydraulic puller for these. We had no luck getting a particular hub off, so left the puller, loaded as tight as we could, overnight.

The next morning the hub and puller were ten feet away, having damaged a motorcycle silencer on their way at high speed across the workshop. To stop this in future we fixed a heavy bowden cable to the puller and the rear spring.

One came off with such force it broke the cable!

A correctly fitted taper and countertaper is an excellent engineering solution, but must be dealt with during installation and removal correctly.

 

[rotrax]

You are correct, one part of the tab would go into the keyway, the other would be bent over the flat on the nut. If there is no way to prevent rotation of the prop on the shaft then there is nothing to lock the nut either.

If the two tapers match properly a light tap into position using a block of wood will stop it revolving on the shaft.

If it does not, dont fit the prop until the mis-match has been rectified.

On a previous boat the tab washer located on the prop boss, between two of the three blades, and was subsequently locked against the flat of the nut.