Glass Sheathing New wood - Methods?

Just doing a new rudder blade for a Prelude using sapele. I've just epoxied the wood and am waiting for it to harden. I'm wondering if it's worth varnishing as the top goes into a headstock and the bottom will be in the water. Will UV be an issue?

epoxiedblade.jpg
 
samwise said:
polyester resin that I had left over from a car bodywork repair job. It was a !!!**** disaster. .
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I was once told that car repair paste is made to absorb water, to help with wet and dry sanding down. Don't quite see the logic in that, all your car repairs would rust really quickly, and they don't.........do they?

For what it's worth the boat in the pic above still has the original 1983 rudder. Inverted 'P' shape, transom hung, 2 x 18mm ply screwed and glued, with 3 x 600gm sheathing, finished with 'flo-coat' type mix, hardwood cheeks bolted either side of the upright. The bolts are above water most of the time. As above though, not worth skimping if you're not confident.
 
Just doing a new rudder blade for a Prelude using sapele. I've just epoxied the wood and am waiting for it to harden. I'm wondering if it's worth varnishing as the top goes into a headstock and the bottom will be in the water. Will UV be an issue?

It will need protection from UV for sure, in fact you should look for a very high UV blocking varnish and don't skimp on thickness or coats.

Good luck.
 
What about the thousands of Mirror dinghies with polyester resin & glasscloth joints between the ply panels, they don't seem to be falling apart. Also, is it not the case that production GRP cruising yachts commonly have the ply bulkheads bonded into place using polyester resin rather than epoxy?
 
1) Re Lakey, epoxy should be varnished with a UV filtered varnish. Avoid 'trad' or Tung oil varnish as epoxy often causes very slow curing, use something like Goldspar or even Perfection.

2) Epoxy is better, but may not be cost effective.
Polyester has less peel strength onto wood. I think it helps to prime the wood with resin diluted in styrene or similar. The best way is to make sure the GRP is strong enough in itself so that the loads are not transferred to the wood very much. This limits the stress put on the joint.
Many good polyester sheathing jobs have been done. Also some spectacular failures. Epoxy is not a silver bullet either. Keeping the wood dry, adequate reinforcement and decent technique are key with either resin.
 
I'll go with the above. The one thing that I would say, is fill and profile internal corners, profile external corners, as it is the corners where any problems will occur, As has been said, you need to build up enough thickness to prevent the wood flexing the interface. Take care if you are going to thin resin with styrene, it is not a nice chemical. Try Cray Valley they have a good tech department. Of course that may be where the resin comes from?
 
JimC said:
What about the thousands of Mirror dinghies with polyester resin & glasscloth joints between the ply panels, they don't seem to be falling apart. Also, is it not the case that production GRP cruising yachts commonly have the ply bulkheads bonded into place using polyester resin rather than epoxy?
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I think the confusion here is that polyester resin does not remain bonded to ply for long if it is below the waterline. Mirror dinghies spend 95%+ of their lives sitting in the dinghy park. Similarly ply wood bulkheads inside a GRP yacht are not in a wet environment, unless a leak develops, when the bonding fails fairly quickly.

On a rudder, I would not consider it, unless the wood is totally encapsulated and remains 100% waterproof, no leaky fastenings, no cracks, no abrasion etc. Once water gets in, it stays there, the join will fail, rot will set in and you will soon need a new rudder.
 
Bajansailor said:
Are Mirror dinghies double taped on all joints, ie taped inside and out?
I think they probably are - they might also have nails as mechanical fasteners, but I am not sure.
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The original build system of the originbal kits was to stitch the ply sheets together using copper wire, then glue glass tape over the seam inside and out to make it watertight. Dont know whether they changed it in later versions?
 
fisherman said:
I was once told that car repair paste is made to absorb water, to help with wet and dry sanding down. Don't quite see the logic in that, all your car repairs would rust really quickly, and they don't.........do they?

.[/QUOTE

FWIW, Fisherman, I once made a test rig using polyester putty (Isopon?) to connect the air lines. Tried to understand the loss of pressure, found it was seeping out of the putty. And, yes, car body repairs will rust if you don't seal the filler with primer/paint etc.
A
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Neville220 said:
I know very well what you are saying is true, and I would be saying the same thing to someone who had posted this, and I might have to bite the bullet and go for epoxy, but I am looking for any possible alternatives.

The foreman at the factory where I get this polyester says it sticks like the proverbial to a blanket but they don't use it for marine purposes.
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In my neck of the woods nearly all home construction is done by stick framing in timber and then sheathing it in ply. Decks, especially those attached or integrated into to the main structure that are treated the same way.

In the seventies and eighties it was very common to fibreglass the decks, in fact an entire industry sprung up around the process. No longer. There were way too many problems with the decks delaminating with subsequent rot problems and this in fairly new structures.

Just a few years ago, I rebuilt our own fibreglassed deck after it rotted off and collapsed after a mere 7 years. I work professionally in that area of business and I do not know of a single fiberglassed deck in existence, either historic or contemporary.

Polyester and wood is not a happy, lasting marriage and no-one can tell me otherwise.
 
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