June 1, 2009

Build a Dinghy: Part 14

Last time, I detailed how the oversized bottom was dry fit and cut to size. Here, you see the results of all that planning, marking and measuring. After buttering the chine logs, the stem and the transom with straight epoxy adn letting it soak in for a few minutes, I next applied a thickened glue mixture containing colloidal silica and milled wood fibers. ( The silica spreads out smooth, a charachteristic I'll appreciate when tooling the squeeze out into beads, called filets ( fill-its) along the chine and bottom. The milled fibers offer greater adhesive strength. So I mixed the two to take advantage of the best properties of both.
After the glue was set, I used a putty knife ground to shape to make my filets and a another putty knife, this one filed knife-sharp, to scrape excess squeeze out. If you catch epoxy at just the right time, you can scrape it smooth. Its way easier than sanding. After the glue fully cured, I used a plane, and then sandpaper, to round the chine and transon/bottom joint so it will take fiberglass better. Glass cloth reinforcement doesnt like sharp corners. I'll be applying +/- 45 6-0z biaxial cloth. Since its not woven, the individual strands dont make all those in and out bends, which is weaker. Additionally, the +/- minus business means the fibers run at a 45-degree angle to one another, instead of at a right angle. When laid across the chine, all the fibers will contribute to strength. With woven cloth, only half the fibers are working, the other half are just along for the ride. Knitted fabric is great. I'll be using peel-ply to provide a smooth finish.
In these pics, you see the chine joint after glueing, scraping, planing and sanding. Looks great, right? Also shown are two views of the dry fit stem. this was machined from VG doug fir, 3/4" x 1." Its glued, and screwed onto the boat with 1-1/2" silicon bronze flathead, square-drive, wood screws. You can see the counterbores I made along its centerline pretty clearly.
The keel adn skeg are next, then the boat gets turned over to work on inwales, outwales, breasthook and quarter knees. Joinerwork--real fussy stuff. But very rewarding.

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