Nanga7 wrote:Couple questions: Fiberglass the rudder or just finish it with coating (and what?).
The downside of coating your rudder is that any covering will add thickness which complicates getting a perfect foil shape. I think that downside is somewhat theoretical. The stock rudder is a hydrodynamic disaster, so about anything will be better (and noticeably so).
If you seal the wood, you will need to be sure that you can keep the skin intact, otherwise you'll have a waterlogged board under the covering. One particular trick is to cut off the forward part of the tip, at an angle, and glue it back on with epoxy. That way, if you hit anything with that part of the rudder, and crack the skin, the waterlogged bit will be limited to that forward tip.
A single layer of glass cloth will increase the resistance against abrasions, etc. and reduce the chance that any contact lets water get through to the wood. My take would be that using a glass layer is a logical consequence of sealing the wood with epoxy. If you are thorough in wetting the cloth with resin, the glass layer will be invisible, if not, just add a thin layer of epoxy to fill in any weave.
Epoxy needs to be protected from UV, so it can't be the outermost covering. You need to varnish or pain it.
Varnish will leave the wood visible and pretty (you will not see the glass) but you cannot use anything to fair the foil. Whatever shape you get after applying the glass is it. (Make sure the varnish has good UV inhibition). (I would opt for a polyurethane, those make pretty hard surfaces - if you seal the wood, the varnish does not need to be as elastic, as there will be no expansion due to moisture cycling).
If you use paint, you can add a thin layer of epoxy-based fairing compound (mix your own, or get pre-mixed, like QuickFair). That allows you to correct any defects in the foil shape. Paint is also a good UV cover, and any damage should be noticeable. (I chose paint. I needed to fair my rudder and the wood I used, plywood, wasn't that pretty anyway - finally, I'm happy with having a white rudder on a white hull).
If you elect not to seal the wood, your basic choice is between oiling or using an oil-based stain or a coating (varnish). I've made poor experience with applying PU varnishes on bare wood - the moisture cycling will quickly crack them. I haven't tried oil-based treatments. I don't know how tolerant they are of the (short term) immersion that you would have with a rudder. Their theoretical advantage is that they are easy to re-apply and that by not forming a layer, they are less sensitive to abrasion (e.g. on the edges of coamings etc), and if damaged more easily repaired.