Prop nuts

zoidberg

zoidberg

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Brass vs stainless.... thin one plus thick one.... securing with cottarpin vs wire locking vs epoxy vs Loctite vs Nyloc....

Pros and contras.....?
 
I have a stainless nut and split pin on a 316 stainless shaft. The s/s nut is OK - stays done up and I can undo it when needed, but the split pin gets bent and damaged. Maybe because I have a drying mooring? If this is so, then other 'external' locking arrangements will also suffer. I would go for Nyloc or Loctite next time.
 
neil_s said:
I have a stainless nut and split pin on a 316 stainless shaft. The s/s nut is OK - stays done up and I can undo it when needed, but the split pin gets bent and damaged. Maybe because I have a drying mooring? If this is so, then other 'external' locking arrangements will also suffer. I would go for Nyloc or Loctite next time.
Click to expand...

You have been lucky so far. A stainless nut can easily become cold welded to a stainless shaft, and become near impossible to remove. Coating the threads with Copaslip or similar may help prevent this.
My original prop had a brass nut which took a zinc anode, and was prevented from coming undone by a stainless tab washer. Current feathering propeller also has a brass nut.

A nyloc nut is likely to be hard to get in the sizes commonly used for propeller fitting, and if stainless would carry the same risk of galling or cold welding to the shaft.
 
Split pin + castellated nut is the best solution if the shaft is drilled. If not I would go for a Nyloc, if available, plus a lock nut, if there is room on the shaft. If no drilling and not even room for a half-width locking nut then Loctite. If the shaft has a flat then a tab washer is fine.

My saildrive shafts are stainless and I've always used stainless nuts without any problems although shafts are copper-greased.

Richard
 
Brass castellated secured to the shaft with a split pin through a hole drilled in the shaft. Wind the nut up to the prop boss finger tight if the split pin goes through the hole all well and good if it doesn't back it off until you can insert the split pin.
 
1.5" Stainless shaft plus stainless tab washer and brass nut from Clements marine.
To much tedious faffing lining up split pins when fitting new set of props and far to much hard work drilling new holes in shafts,
Nuts £22.00 washers £5.00 ?, not sure if your supposed to reuse washer but everybody appears too without disaster.
 
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petehb said:
Brass castellated secured to the shaft with a split pin through a hole drilled in the shaft. Wind the nut up to the prop boss finger tight if the split pin goes through the hole all well and good if it doesn't back it off until you can insert the split pin.
Click to expand...

That's interesting Pete. I have always tightened up castellated nuts with a spanner until fairly tight (say 15 - 20 Nm although not using a torque wrench) and then backed off to fit the pin. Your system is much looser and would probably not even register on a torque wrench scale.

Richard
 
RichardS said:
That's interesting Pete. I have always tightened up castellated nuts with a spanner until fairly tight (say 15 - 20 Nm although not using a torque wrench) and then backed off to fit the pin. Your system is much looser and would probably not even register on a torque wrench scale.

Richard
Click to expand...

Yes it's simple you rarely have to back the nut off much more than half a castellation if it was more you could nip it up if you were really worried about a gap I suppose you could back it all off and put a washer in but even a thin one is likely to take you out of the place you were at. The prop is on a keyway and is not going to move very much if at all. It served on two boats for 18 years so I know there were no problems. A locking tab is the obvious alternative especially if the shaft isn't drilled.
 
Some years ago a well respected marine engineer told me that it was difficult to get a castellated nut in a decent material bronze or stainless. His solution was to use a plain nut tighten the nut against the washer and prop and mark the position of the nut face. He would then drill the shaft fit a split pin making sure that the hole was just too close to the nut. you then just skim grind the face of the nut until you got a nice tight fit between the nut and the split pin. Probably a bit out of date now with good quality castellated nuts available, but if you have a plain nut, washers and a hole in the shaft you could always file the fit in an emergency.
.,.
 
Just done mine, stainless shaft, bronze prop with a large brass/bronze nut with a 3mm split pin drilled through, followed by a half nut done up tight.
 
I now have an Autoprop, which has a grub screw, tapped through the prop boss, which tightens onto a cylindrical part of the nut, which instead of being aft of the prop, is actually inside it. Very simple.
My previous (big) boat had an interesting set up. She had a 49" four bladed propeller on a 3.5" shaft. A large cone nut held the prop on, but a 3/4" bronze set screw was then tightened through the end of the cone, into a tapped hole in the end of the prop shaft. Either the nut or the screw was LH and the other was RH. I now cannot remember which, but it worked and was very simple.
 
Interesting comments.

Brass? Since removing copper sponge nuts from my companionway door (they used to be brass) I have always gone bronze or stainless.

How is the prop locked onto the shaft? If it is keyed, then nut tightness is not critical. If it relies on locking onto a taper, then nut tightness is more important.
 
I thought this OP might throw up a couple of interesting points.

Here's a link to a pair of vids showing 'the full monty'.....
 
Graham_Wright said:
How is the prop locked onto the shaft? If it is keyed, then nut tightness is not critical. If it relies on locking onto a taper, then nut tightness is more important.
Click to expand...

Either way, I've never heard of a prop nut being finger-tight, which would not register on a torque wrench, and then being backed off before being pinned. In engineering terms this is perhaps "negative torque". :o

The only example I can think of which equates to "negative torque" is tapered bearings in some car wheels .... but these are a moving part. :confused:

Richard
 
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