Rudder shaft

[Javelin]

I noticed I had a bit of play in my spade rudder.
The play actually seemed worse fore and aft than athwart ships although there is some play there as well.

I dropped the rudder and popped the alloy rudder tube out so I could inspect and then replace the delrin bearings.

However the bearings actually seemed pretty good and on closer inspection it appears that the aluminium shaft has worn slightly in the bearing location.

Not sure if the worn area is perfectly round and given the difference in play I suspect it won't be.
So my initial plan was to fare it with Epoxy/alloy/graphite but;
how do I make the shaft round again given it's attached to a bloody great lump of Glass and foam at one end, so not easy to get in on a lathe.

Anyone got any bright ideas?

 

[TQA]

You need an old style fitter, a man who can use a draw file and a straight edge.

I am not sure about the bearing quality of epoxy though.

 

[TQA]

You need an old style fitter, a man who can use a draw file and a straight edge.

I am not sure about the bearing quality of epoxy though.

 

[30boat]

You need an old style fitter, a man who can use a draw file and a straight edge.

I am not sure about the bearing quality of epoxy though.

Epoxy mixed with graphite powder is a reasonable bearing material.
You could epoxy a thin round metal sleeve over the worn area.If the rudder shaft is aluminium you'd have to be careful about galvanic interaction.

 

[Javelin]

yes looks like a long laborious job by hand.
The wear is the first 5" just above the rudder which leaves a good 12" of pristine shaft above before it then tapers down to 2" for the top bearing.
So sliding a sleeve is not really an option because of the untouched shaft above the wear.

The wear is not even and varies from a couple of thou to 1/16" and slightly oval.

One idea I've had is to wrap the pristine section with 120 grit wet and dry and then glass over it using 100mm glass fibre tape giving me in theory a copy of the shaft proper.
Then after coating the wear area with Epoxy/grapite/ali mix use the wet and dry to make good.

 

[Neil_Y]

If you have the space you can slip a thin composite bearing over the Al rudder stock and bed this on epoxy, 5mm wall thickness would ensure it was round and still easy to make, you can then run this in a composite bearing epoxied into the hull. If you try and make a sleeve yourself it will be difficult to get it round unless it is machined after moulding and it needs a very good finish where it will work against the fixed bearing material.

You can't just make a bearing material that is any good by just mixing epoxy/graphite you have to know the thermal expansion and moisture absorption rates to be able to determine the clearance otherwise you may suffer from a seized up rudder if the weather turns warm! Maritex has two types of dry run lubricants and we know the thermal and moisture swell so we can machine bearings to an accurate clearance allowing for these changes in diameter.

We've just done a similar job on a carbon square rudder stock in this picture, it shows the square rudder the filler as well as the inner and outer bearings.

 

[Javelin]

Thanks for that Neil I'll keep it in mind.
Unfortunately I had decided to try the graphite/west method today so missed your post.
I did however take some photo's of the procedure for my MG34 site see here

Oh and Neil, it might be worth getting someone at work to check the website as its not good for me using Chrome, quite a few 404 errors from the menu etc.

 

[Neil_Y]

Thanks for that Neil I'll keep it in mind.
Unfortunately I had decided to try the graphite/west method today so missed your post.
I did however take some photo's of the procedure for my MG34 site see here



Oh and Neil, it might be worth getting someone at work to check the website as its not good for me using Chrome, quite a few 404 errors from the menu etc.

Thanks for the website comment, it's long overdue for re design! Fingers crossed for your repair.

 

[Javelin]

The epoxy and fairing tool worked pretty well tbh.
Not perfect but not bad.

Anyway I took various measurements of the tube, shaft and bearings as can be seen on the final photo here

Do you think there is enough scope with the bottom bearing to fit a collar on the shaft?
Is the top bearing just a question of getting a new bush?

 

[Neil_Y]

I've asked our materials expert to have a look at what you've done (he's a guru on matalurgy and composites) in terms of our composite bushes when you suggest a collar on the shaft are you thinking of fixing the bearing to the shaft and have it sliding in the rudder tube?

We need to know which side you want fixed (ID or OD) and what it is bonded to (we prefer epoxy bedded bearings) and what material it will slide against, this can be Al/SS or composite. We also need accurate sizes of the carrier and shaft to work out clearances.

A drawing usually helps

 

[Javelin]

OK, lets see if I can my head round this.
The rudder tube sits inside a glass fibre tube glassed to the hull/cockpit floor with an ID of 100mm
It slid out with a bit of nurturing and didn't appear to have anything keeping it in other than the fact it is a tight interference fit.

The alloy rudder tube has an ID of 94mm - (3mm walls = 100mm dia ali tube)
The lower part of the shaft has an OD of 75.8mm

So if I ran with the shaft as is, I'd need a bearing of 18.2 thickness by 78mm long or there abouts. (length not critical as there's plenty of shaft above current bearing location)

However if I understood your earlier post I could epoxy a 5mm thick sleeve over the shaft which would then mean the shaft OD would be increased to 85.8mm which in turn would only leave 8.2mm for the tube bearing or in other words a 4.1mm thick bearing.

Would 4.1mm be enough for a bearing?
The Rudder tube I guess would keep it in shape and it can have a 3mm flange at one end by 7mm long.

The top bearing is a lot easier as its just a 69mm OD x 47.5mm ID x 76mm long bearing. (nylon by the look of the old one)

Measurements and photos of shaft, tube, bearings are all at http://www.mgrs34.info/albums/somersault-repairs/

 

[Neil_Y]

Our advice is to remove graphite as this is likely corrode the aluminium shaft through galvanic action if it is in sea water.

You have 9.00mm between the rudder shaft and the rudder tube (94.00 tube, 76.00 rudder stock). We would use a 5.00mm sleeve epoxied onto rudder shaft to give a true round bearing surface and then install a 4.00mm thick bearing in the rudder tube. You then have a perfect machined bearing surface with known clearance. We wouldn't want to be involved in the rudder system with any of the graphite present.

 

[30boat]

Our advice is to remove graphite as this is likely corrode the aluminium shaft through galvanic action if it is in sea water.

You have 9.00mm between the rudder shaft and the rudder tube (94.00 tube, 76.00 rudder stock). We would use a 5.00mm sleeve epoxied onto rudder shaft to give a true round bearing surface and then install a 4.00mm thick bearing in the rudder tube. You then have a perfect machined bearing surface with known clearance. We wouldn't want to be involved in the rudder system with any of the graphite present.

What would you make the sleeve out of?To me that's the best aproach.
Graphite on aluminium may not be a good idea indeed.

 

[Javelin]

OK, many thanks.
The lower bearing 6" above the water level at rest.
The top 5" of rudder is always clear of growth, barnacles etc
However I take your point and will remove it which due to the very thin layer wont be hard.

I guess my next course of action is to contact h4marine direct.
Thanks for the help.

Photo of sister ship - can just about make out the rudder sticking out of the water.

 

[Neil_Y]

What would you make the sleeve out of?To me that's the best aproach.
Graphite on aluminium may not be a good idea indeed.

As Maritex works well as a bearing on Maritex we would sleeve the shaft with a Maritex tube bedded on a thin layer of epoxy. Then install a Maritex bearing in the rudder tube again bedded on epoxy.