making a rudder

[Spuddy]

my old boat is on the hard and after poking around there are some priority problems to do with the rudder. I'd really appreciate suggestions from anyone with experience of :
making a new rudder. Old grp one is splintered at bottom and cracked along seam at top. It's repairable but the internal metal straps have obviously had it. My thought is to build up a new one out of ply. What material for the new tang things and for the new shaft? Shape of rudder is very like a folkboats with a cut out for prop halfway down. This means shaft can only be bonded in at top with the tangs only strapping everything together in the upper third. Bottom of rudder swings on end of keel from a SS pivot.
My thoughts were to clad the new one in cloth and epoxy. Any advice on adhesive for laminating up the ply? I've used the polyurethane Balcotan stuff on a friends ply trailer sailor but any ideas about prolonged immersion.

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[Evadne]

I have a similar arrangement to yours, but a wooden rudder. When she was new (to me) I had to replace the stock and the boatyard got a stock made up of s/s bar and a s/s pipe with a tang welded to it. This was clamped between the two planks of mahogany that made up the original rudder (you could use 12mm ply), screwed and glued and filled with gunge. They were a fairly traditional East coast boatyard and seemed to know what they were doing, which is more than coiuld be said for me had I tried to do it myself. Years later I had to add a new bit to the trailing edge, when part of it fell off. I built it up with 38mm square lengths of hardwood, screwed and glued with epoxy and planed to shape.

Both these types of construction have lasted quite well (I've had the boat nearly 20 years). You could coat with grp but I'm not sure what the advantage would be. You might keep the water out but if any got in, it would never get out again, in my opinion.

The S/S stock and tang has lasted well, despite the usual caveats about crevice corrosion. Just a bit of crevicing on the lower end of the stock. I guess there is enough oxygen around them for this not to be a problem. You could go for a hot-dipped galvanised steel construct if you prefer, or bronze if you're really rich.


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[graham]

I think that by the time you have paid for the plywood ANDthe epoxy ,glass cloth etc you may find it cheaper and a better job to make it out of solid timber .

Personally I would look into making it from solid Iroko.This is a very stable hardwood which can survive constant immersion without rot.It is almost as good as Teak but for a fraction of the price.

The Rudder on my boat is Iroko and still as sound as when new in 1980.

Bet of luck with the project.

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[oldharry]

Sunds OK. Balcotan should be OK underwater, but you could equally well use epoxy resin provided the ply is properly dry (i.e. stored indoors), and get an even stronger joint.

Sheathing will help to protect the end grains of the ply, which are always the weak point, but - and its a big but - should the sheathing be punctured, or should any fastening through it work and loosen, water will get in, and never come out again, leaving almost ideal conditions for rot to develop.

Ply is not the ideal material for the rudder of a larger boat because end grains are vulnerable. Dinghy rudders are very rarely subject to long term immersion, so ply is used in most cases. Larger boats that remain afloat do better with a good hardwood.

A further option is to rebuild the original rudder which is presumably GRP. It is not all that difficult to cut round the edge of the moulding to release the two halves to remove the original metalwork. This can be used as a pattern, and it takes very little skill to repair the damaged areas, mount the new metalwork, and stick it all back together again as good as new. It is easier and much neater to use glass fibre tape over the joins.

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[webcraft]

Emergency Rudders article

This has got some interesting thoughts on rudder construction using closed cell foam and grp.

Read it <font size=1><A target="_blank" HREF=http://www.bluemoment.com>http://www.bluemoment.com</font size=1>

 

[Spuddy]

thanks everybody - much appreciated.
It's making my mind up. There are pros and cons for all the alternatives.
one thing I'm wary of is fixing rudder blade and stock together permanently without being able to offer it up. Ground gets in way of sliding the assembly upwards into the tube and funds will not allow yet more hoists by yard.
I was contemplating bunging the stock up the tube then temporarily bolting the blade on to check alignment and to mark up accurate bolt holes. If all ok, go ahead with fixing and bonding. This would rule out simplest option of repairing existing grp rudder unfortunately.... unless....


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