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Mahogany below the water line


Jim Stumpf

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What is the best way to finish bright mahogany below the water line. On the Oxford dinghy that I am refinishing I used Cetol Marine Light on the rails and seats but I'm not sure how that would hold up on the rudder. The new skeg is white oak which I painted, the new center board is mdo ply, glassed and painted but the rudder is the original and a very beautiful one at that, what is the best way to keep it looking good?

Thanks,

Jim

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Jim, I would look for a marine type oil finish and apply a number of thinned coats to get it soaked in. I'd start with maybe a 30-70 mix (30% oil for the first couple of coats) and warm the wood and oil a bit so it soaks in deep. Let the oil stand for awhile and then wipe off the excess. After a couple of thin coats, I'd go to a 50-50 mix for a couple and finally some straight oil. Once that has cured (really well) I'd put some varnish on it to make it shiny.

After that, you might have an annual varnish in the spring but the wood itself will be protected anyway.

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Is this a dry sailed boat or one that is kept in the water?

My boat has a solid mahogany rudder and they still make them new. They are intended to be dry sailed, and come with about 4 or 5 coats of some type of spar varnish....and that is all. Curious, as almost any clear coat or varnish you look at will say it's not for use below the waterline. If you didn't trust the varnish alone, you could coat it with 4 or 5 coats of clear epoxy and then a couple of coats of polyurethane or clear coat paint over that. System 3 sells a clear two part water based LPU paint for use over epoxy. Again, instructions for this say it's not for use below the waterline.

If kept in the water, the next question is salt or fresh? Apparently salt water works well with mahogany and actually pickles it. In fresh water, mahogany turns black and starts to rot. And if kept in the water, you have fouling to worry about, so it's not likely that will be left as a clear coat, but rather painted with anti-fouling.

On my mahogany rudder kept in fresh water, it got a layer of glass and 4 coats of epoxy, and anti-fouling over that...below the waterline. Above the waterline, 3 coats of epoxy and 3 coats of Ephiphanes wood finish gloss. It looks good and touchup just requires a light sanding and two more coats of varnish.

Howard

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The dinghy will be drysailed on fresh water. I was inclined to use spar varnish myself but as you said the manf. does not recomend it for below the water line. The oxford is 10ft long with a 5ft beam, cat riged gunter. She is very sweet and I can not wait to launch her now that the weather has started to break, although there is still some ice on the local reservoir.

Thanks,

Jim

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Jim,

Usually when Manufactures say not suitable for below the waterline they mean not more than a few days of total immersion. So if you're going to dry sail I'd coat the rudder with 2 coats of epoxy, and then 3 coats of marine varnish. The epoxy is a good "primer" for the varnish. Most times varnish lifts because of moisture getting between it and the substrate. The coats of expoxy will "slow" this the adsorption of water into the wood. This advise comes from most of the epoxy vendors (i.e. West System, Sytem 3, and Raka). I did this with my rudder and haven't had any problems....of course you should "freshen" the varnish every year - lightly scuff the surface and recoat with fresh varnish.

Good luck

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