Tightening propellor bolts

webcraft

webcraft

Well-Known Member
Joined
8 Jul 2001
Messages
40,411
Location
Cyberspace
www.bluemoment.com
.
When we bought Avy-J we antifouled her, launched her and sailed/motored her down to our local yard before lifting herback out for refitting. We then noticed the prop locknut was loose.

I finally got round to tightening it today and noticed that the top nut (nearest the prop) was also slightly loose. These seem to be bronze nuts on a ss shaft.

Is there a specific torque, and should I use some form of loctite or similar?


- W
 
“Top nut”? Are you saying there is more than one? The usual arrangement is a castellated nut and a hole in the shaft through which you can fit a split pin. On a stainless shaft the nut should be brass.
 
webcraft said:
.
When we bought Avy-J we antifouled her, launched her and sailed/motored her down to our local yard before lifting herback out for refitting. We then noticed the prop locknut was loose.

I finally got round to tightening it today and noticed that the top nut (nearest the prop) was also slightly loose. These seem to be bronze nuts on a ss shaft.

Is there a specific torque, and should I use some form of loctite or similar?


- W
Click to expand...

The nut closest to the to the prop should be tightened first to ensure the prop is tight on its taper. If it is loose the key may become damaged or even shear. It would be a good idea to remove the prop, if you can, and check the key although it is the tightness on the taper which should transmit the driving torque rather than the key

The second nut, should be tightened against the first to lock it. If you have a full nut and a half thickness nut the half nut goes on first, followed by the full nut ( although I bet that will be contested).

Loctite might be a good idea. ............... Sorry cannot help with torque figures

If the shaft is drilled for a split pin then a castellated nut, as suggested by Porthandbuoy, would be the more sensible.
Brass can dezincify, bronze wont, so I don't know why he is suggesting brass
 
Last edited:
Bronze nuts on a SS shaft are fine - either you should be drilled for a split pin or, if not, there should be a tab washer as Fr J says. There is no need to torque as it's the taper that does (should do) the work. Just use the first nut to get the prop hard onto the taper then use the second (with either a tab washer or pin) to lock the first nut. No need for loctite or whatever.
 
Did have a boat where bronze prop nut was not tight on stainless shaft., attempted to retighten.
Thread simply crumbled away .
When replacing shafts later, used stainless lock washers and stainless loc-nuts.
Split pins and castellated nuts simply too much hard work.
 
Last edited:
No castellated nut, no hole. Just two equal size bronze nuts. What exactly is a tab washer and how should it be fitted? (There is only 1 thread sticking out of the 2nd nut)

- W
 
webcraft said:
No castellated nut, no hole. Just two equal size bronze nuts. What exactly is a tab washer and how should it be fitted? (There is only 1 thread sticking out of the 2nd nut)

- W
Click to expand...

A washer with a "tab" or two tabs sticking out of the side that you bend up/ down the side of the nuts to stop them undoing .......... Goggle it !

If appropriate the washer may also have an internal tab that locates in the shaft key way .

BTW Bronze nuts are used to avoid the risk of galling if stainless steel nuts are used on stainless steel
 
Last edited:
webcraft said:
No castellated nut, no hole. Just two equal size bronze nuts. What exactly is a tab washer and how should it be fitted? (There is only 1 thread sticking out of the 2nd nut)

- W
Click to expand...

A tab washer isn't going to be that useful unless the threaded part of the shaft has a flat machined into it.

My saildrive prop shafts were stainless and had no flat so I used two stainless nuts locked together, the outer of which was a Nyloc. No need for Loctite. :)

Richard
 
RichardS said:
A tab washer isn't going to be that useful unless the threaded part of the shaft has a flat machined into it.

My saildrive prop shafts were stainless and had no flat so I used two stainless nuts locked together, the outer of which was a Nyloc. No need for Loctite. :)

Richard
Click to expand...

Yes, a Nyloc makes sense. Can I use the inner bronze nut and replace the outer nut with a SS nyloc?

- W
 
webcraft said:
Yes, a Nyloc makes sense. Can I use the inner bronze nut and replace the outer nut with a SS nyloc?

- W
Click to expand...

Using a stainless nut in a high assembly torque situation invites galling, a process whereby the nut and shaft are effectively cold welded together, and become very difficult to get apart.

The best prop nut arrangement I have seen is the one used by Jeanneau, Their prop nut is a conical bronze one with two spanner flats. A stainless tab washer has an internal tongue to engage in the shaft keyway and is bent up after fitting to engage one of the flats on the nut. The end of the nut extends beyond the shaft end and takes a zinc anode held on by a central Allen screw.
 
Last edited:
Norman_E said:
Using a stainless nut in a high assembly torque situation invites galling, a process whereby the nut and shaft are effectively cold welded together, and become very difficult to get apart.
Click to expand...

That's true, although the use of stainless nuts on stainless threads is the Yanmar standard fitment and is also commonplace elsewhere and galling is solved by a dab of copper grease/ ordinary grease or similar, which is what I always use on all threads, including my prop shafts.

Richard
 
Last edited:
.
Many thanks to all responders, I realise a castellated nut or a locking washer locked against a flat on the shaft are the best options but . . . my situation is what it is - no hole for a pin, no flat on the shaft, currently just two bronze nuts on the stainless shaft. I am not going to be fitting a new shaft any time soon.

As I see it, realistic options are:

a) Use the existing brass nuts with loctite on the outer nut

b) Use the inner brass nut and an outer SS nyloc

c) As above but replace inner nut with plain SS nut as well.

My impression from reading the answers so far is that b) is probably the best bet. (Thanks Richard). Would the nyloc avoid the SS to SS galling problem? (No point in putting grease on a nyloc).

And . . . I presume it is OK to torque the nuts up against the gearbox (i.e. put the engine in gear) ??


- W
 
Last edited:
Tab washers don't have to have flats on the shaft, they can be used with the tab fitted into the keyway groove, or into a shallow hole drilled into the prop.

https://www.fastenerdata.co.uk/fast...nal-tab-washer-stainless-steel-a4-din462.html

However, if you fully tighten the first nut, then fully tighten the second one against it, that's good enough. If you feel inclined to put some Loctite on the second nut, it won't hurt.

Stainless nuts would not be my choice, if you suffer from galling you'll need to replace the shaft ! Nyloc nuts do not reduce the risk of galling.
 
I don't think the nyloc in itself will prevent galling as it's not stopping the steel to steel contact. However, a tiny touch of grease at the point where the threads will overlap once the nut is tightened will stop it although the chances are that it won't happen anyway. It won't have a major effect on the nyloc.

You might get sufficient torque (maybe 50 - 70 Nm should be sufficient if you can't find a specific recommendation) with the engine in gear against compression. If you don't, you can lock the crankshaft with a large spanner on the pulley nut. This is the method recommended by Yanmar but I don't like it and I prefer to jam a block of wood between the prop blade and the hull. :)

Thinking about that torque range, with a bronze nut perhaps you need to go low rather than high but without knowing more about the shaft and the thread it's difficult to be sure.

If you have a groove in the shaft extending beyond the end of the prop then you don't need a flat. However, I had assumed that a locking washer would already be in place if that was the case. :)

Richard
 
Last edited:
You must log in or register to reply here.

Share this page

Top