View Full Version : Repost - Transom Interior

Jim Hillman
07-11-2005, 01:50 PM
Posted by remydogart (Member # 1809) on 06-20-2000, 05:33 PM:

I replaced my transom with mahogany planking. The outside is finished, but how should I treat the interior of the planking? Should I just leave it bare wood? I was once told that it should be left alone so it can breathe any suggestions?

Posted by Ed Harrow (Member # 1235) on 06-20-2000, 08:15 PM:

My (limited to be sure) experience with wood finished on one side and left bare on the other (large pieces, not well fastened, outdoors and in the weather) has not been particularly good. The wood gains/looses moisture unevenly with a predictable result.
Might not be so with the planks of a transom, but I don't think you're likely to go wrong finishing both sides, or soak it in CPES. Everything that's ever been written here with respect to CPES is that it's a nearly magic solution to peeling finishes.

Now there's a Shakespeare quote about free advice, if only I could remember what it is...

Posted by Ian McColgin (Member # 32) on 06-21-2000, 10:18 AM:

Despite living now on a goosealed boat, I can harken back to Goblin's transom, georgous varnished mahogony. It was unpainted unsealed on the inside. Every couple years I'd cuprinol it, that part of the boat being far enough away from living space that I was unafraid. Like so many Alden sterns, it would have been prone to rot escept that I had a huge (6"d) vent right in the middle of the deck to provide air and serve as a good place for spontaneous mainsheet snubbing during gybes.
Vent the area & you'll be fine.

Posted by Art Read (Member # 994) on 06-26-2000, 06:25 AM:

I wouldn't worry too much about putting some sort of finish on there. Painted wood "breathes" just fine. "Bare" wood is just asking for trouble, especially in an out of the way, poorly ventilated area like the ends of a boat! If it were mine, I'd put on some CPES and follow it up right away with red lead primer before it cures. Get all the faying, wood to wood joints as well. Lots of articles in Woodenboat about "restoration" projects on boats that were put together "dry" years ago.... Notice the pictures all show the new wood going in freshly primed?

Posted by Allen Foote (Member # 798) on 06-27-2000, 07:15 PM:

Coat it with varnish on the inside also. First coat thinned and then 2nd coat full strength. Just enough to keep the moisture of condensation ect. from soaking in.

Posted by Oyvind Snibsoer (Member # 300) on 06-28-2000, 03:56 AM:

According to my Old Man, who use to be an engineer in the paint industry before he ventured into foodstuffs, sealing all sides of a plank which will be exposed to moisture is asking for trouble. This is also the conclusion in an excellent manual on preservation of traditional boats published by the Norwegian Custodian General. Yes, you can paint (or varnish) both sides of a plank in a boat, but they specifically warn against using modern alkyd(?) based paints on the inside (I don't have the book available at present, so I may be incorrect on the term). Anyways, the point is that the modern paints are nearly impermeable to water, which will effectively trap any moisture that finds its way in through joints, "holidays" and pinholes. Traditional linseed oil based products such as red lead may be fine, though, as they allow the moisture to escape without problems, and probably also the CPES.

Posted by Scott Rosen (Member # 1201) on 06-28-2000, 09:40 AM:

I'll venture a guess that the "modern" paints referred to are the two part linear polyurathane and other similar paints. They are very, very water resistant. Alkyd resin paints are usually linseed oil based and are not impervious to water. Lots of so-called traditional paints and varnishes use alkyd resins. Lots of boat hulls are painted inside and out with alkyd resin paints and varnishes with no ill effects.

Posted by Art Read (Member # 994) on 06-28-2000, 01:31 PM:

Oyvind and Scott... Good point! I'd never thought of that... I wonder how many folks put that two part stuff all over with the best intentions in the world, never realising the potential problems? I might very well have if some slick enough salesman had gotten ahold of me. I hope you're right about the red lead, cpes, alkyd resin paints, etc. properties. I think we're all agreed that "encapsulating" wood is a dangerous course unless one is willing to take pains to make sure that water NEVER again gets near that wood, but even then, it isn't an appropriate treatment on a boat that wasn't designed for "monoque" (sp?) construction. Besides, I can't imagine a more complete "encapsulation" regimen than these 'glass boats with wood cores. And even they still get soggy! I just read about a 'glass trawler that was being retrofitted with keel cooling and air conditioning units. When they drilled through the transom for the mounting bolts, they had to wait a day and a half for the water to stop draining out of the core! It came out as a steady stream when they first drilled through the 'glass. I'm just very leary of boats with unprotected wood hidden away inside. I've crawled around a lot of lazzerettes on old, wooden boats, and every time I came across unfinished timbers, the musty smell and "fuzzy" feel and appearance of the wood gave me a very uneasy feeling. Where I tried a little, after the fact, preventitive painting, often the paint wouldn't even "stick". Another boat that had to have her entire, (unprotected) stern replaced still looked great 15 years later. Every single, new piece of wood that went into her had red lead liberaly coated everywhere... This may just be anictdotel experience on my part, but it's certainly swayed my bias on the subject.
(BTW... Oyvind... Is the Custodian General's book published in English? Still available? Sounds like something I'd like to read...)

Posted by Allen Foote (Member # 798) on 07-02-2000, 08:51 PM:

Have you ever seen the black spots on a varnished transum where moisture came through the wood to the surface and ruined an otherwise perfect job? All boats are a compromise and all techniques can be disputed. I'd rather coat my transum with varnish and take my chances on its "self distruction" than wood and refinish annually.

Posted by Oyvind Snibsoer (Member # 300) on 07-03-2000, 04:30 AM:

Sorry, I don't believe the Custodian General's book is available in English, but it's still in print.
BTW, coating the outside of a plank with a waterproof sealant such as a modern varnish is presumably OK, just make sure that moisture can escape on one side (inside) of the plank.

Another interesting point about conserving and protecting wooden boats, taken from the book, concerns winter layup and measures taken to reduce the moisture levels below decks. The Norw. Maritime Museum found that the most efficient way to reduce the moisture level in their schooner "Svanen" was to install a dehumidifier. In winter time, just providing forced ventilation was never able to reduce the humidity to levels lower than that of the atmosphere. This level was usually above the growth level of rot spores (40%?). Installing dehumidifiers lowered the humidity to levels well below this, and has greatly reduced maintenance costs.

Posted by John R Smith (Member # 960) on 07-03-2000, 05:06 AM:

Humidity? You ought to try Cornwall. Even in the summer, RH (relative humidity) here averages around 70%. In the winter, wetter of course. The lowest I have seen was 50% on two days last year.

Posted by Jorma Salomaa (Member # 793) on 07-03-2000, 07:00 PM:

My conclusion has been that it is better to paint a boat inside. The reason is that it prevents water from immediately soaking into the wood. Water comes through a leak in the deck or by condensation. On a painted surface the water will have time to evaporate before it soaks in. But therés no need to seal the wood. In my opinion, one thin coat is enough. It doeśnt look finished, and those who are disturbed by that paint two. Anything more is overkill and will, at some time, result in peeling paint and lots of trouble. If you use red lead and put it on thinly it will stay there for ever. The same goes for Yacht Primer II by International (the silver colored bottom primer). Íve also used boiled linseed oil diluted with turps, and diluted varnish. CPES would be fine. Owatrol would be fine. Cuprinol is excellent if you can stand the odor. I think the whole point is that we dońt need UV protection or abrasion resistance here, only a chance for the water to either evaporate or to run down some place, hopefully into the bilge.
[This message has been edited by Jorma Salomaa (edited 07-03-2000).]

Posted by Allen Foote (Member # 798) on 07-04-2000, 01:38 PM:

Thats it....thanks Jorma.


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