Join Date: Mar 2006
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In general, structural repairs should be done with epoxy, especially if you're not proficient or familiar with polyester and vinylester resins and their use. This is for several reasons.
First, epoxy resins are generally easier to mix and more forgiving of small errors in measurement than polyester/vinylester resins. Most epoxy resins are a 1:1, 1:2, 1:3, or 1:4 ratio and are not dependent on temperature or other variables for changing the mixture ratio, which can be the case with polyester/vinylester resins and their catalysts.
Second, epoxy resins have far greater secondary (adhesive) bonding characteristics than do polyester or vinylester resins. This means that the bond between the repair and the original material will generally be stronger when using an epoxy resin.
Third, epoxy resin is more resistant to water or moisture intrusion, since it is generally less permeable to water than vinylester or polyester resins are. Polyester resins are generally the worst with regards to osmosis or water permeation. Vinylester resins are better than polyester resins.
I would use 6 oz. or 10 oz. cloth, since you're really not trying to build a lot of thickness or strength here. Ideally, you should use a layer or two of kevlar under a couple layers fiberglass, then fair the fiberglass with thickened epoxy. The reason for this is simple—kevlar cloth has very good abrasion resistance and it will make the rudder far more damage resistant than just fiberglass cloth alone. However, kevlar cloth has a nasty tendency to float in most resins and is impossible to sand fair, so putting a couple layers of fiberglass over it is usually necessary.
You shouldn't need a barrier coat, since the epoxy layup is pretty good at resisting osmosis.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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