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Old 07-16-2013
Brent Swain Brent Swain is offline
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Re: Pros and cons of steel sailboats

My steel came wheelabraded and primed with carboweld cold galvanizing zinc rich primer, 85% zinc dry weight. I touched up the welds with a similar product, washed all the welding smoke off, with first TSP then vinegar then water, let her dry, then gave her 5 coats of bar rust 235 brown on the hull, three coats inside, and four on the decks. The thicker the epoxy the better. This I covered ,for colour and UV protection with marine enamel. Epoxy gets continuously thiner under UV. I give her another coat of cheap marine enamel every few years. To get anything to stick to epoxy, you have to put your first coat of enamel or urethane on the last coat of epoxy, wet on wet. Otherwise it will fall off in sheets.If you are using epoxy tar, it will bleed thru and look like hell. Give it another coat in 24 hours, then leave it alone for several weeks, to harden up well. Then you can put any colour you want over it , including white, and it will not bleed thru .
For commercial boats, where the epoxy is constantly getting knocked off, sandblasting and a buildup of zinc primer will not get knocked off, and can be overcoated with more zinc primer any time.

Waser makes good zinc primers.
Origamiboats, being as fair as any fibreglass hull, need no fairing, but if you have a hull you have to fair, then fairing is best done from the inside , with a hydraulic jack on a telescoping pole. Where the hull is dished inwards, you tack a length of flatbar on the inside of the bulge, then force it out with the jack ,and put several tacks along it. When you release the jack, it will stay fair, far more permanently that any filler. You can find the hollows with a flashlight, shone along the hull after dark. Do the whole inside of the hull this way, wherever there are hollows. Dont worry about what it looks like inside, that will be covered with many coats of epoxy tar and sprayfoam, and never seen again. It's the outside, and minimizing filler which counts.
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Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"

Last edited by Brent Swain; 07-16-2013 at 01:19 AM.
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