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Thread: Last rudder question- I hope!

  1. #1
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    Default Last rudder question- I hope!

    The barndoor rudder for my catboat build is made from 3 layers of 1/2' Meranti plywood. It's all shaped and sanded, ready for the paint to match the hull (Petit Easy-poxy). Does it need to be fiberglassed first? My thought is to just give it a coat of penetrating epoxy, then paint. What say you?

  2. #2
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    Default Re: Last rudder question- I hope!

    The rudder on my boat was glassed in the late 90's & when I pulled it off in 2010, it musta weighed 250 lbs. Inside was a stew of water & wood fibers - IOW the only thing holding it together was the glass.

    My replacement is solid wood & no epoxy at all - just bottom paint. Weighs maybe 75 lbs.

    However, plywood will want more sealing. Not to get into the whole CPES debate (though I like it), but I'd think some good sealing would be in order.
    "If it ain't broke, you're not trying." - Red Green

  3. #3
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    Default Re: Last rudder question- I hope!

    As far as I know, the only epoxy that is waterproof is coal tar epoxy. All other epoxy, and other sealer finishes, allow water to pass through in the way of semipermiable membranes. One document I have seen says that 6 layers of epoxy-glass will keep out 99% of water. With semipermeable membranes, water comes in under pressure (in the water) but doesn't come out when out of the water as there is only gravity for pressure, unless the water inside has caused the wood to swell and break the FRP skin. I'd seal the edges where endgrain shows, maybe with putty, and paint, assuming that the plywood is proper marine plywood. Good luck.

  4. #4
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    Default Re: Last rudder question- I hope!

    Meg's rudder (and leeboards) are plywood layers, CPES, thicker epoxy, paint.

  5. #5
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    Default Re: Last rudder question- I hope!

    I'd say yes to CPES, glass and paint. Does it ever come in contact with the bottom when beaching or launching?
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  6. #6
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    Default Re: Last rudder question- I hope!

    Quote Originally Posted by Thorne View Post
    I'd say yes to CPES, glass and paint. Does it ever come in contact with the bottom when beaching or launching?
    It will be only trailer-sailed, with little or no beaching at all.

  7. #7
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    Default Re: Last rudder question- I hope!

    Then you don't need to add thickened epoxy to the leading and bottom edges -- but I'd do that anyway to protect the ply. I like gluing a piece of nylon cord to the edge, then building up heavily thickened epoxy around the line.
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  8. #8
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    Default Re: Last rudder question- I hope!

    epoxy resin, barrier coat, and paint.

    Don't waste your time trying to load up end grain with CPES, it is so absurdly thin. A conventional resin mix will soak into end grain just fine, particularly with some warmth.

    System 3 S1 has more solids than Smiths CPES but is still eminently brushable for sealing bare wood.
    Really nothing against glassing the rudder other than more work and expense - perhaps a question of environment and usage.

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