May 28, 2009

Build a Dinghy: Part 13

After installing the chines and sanding/planing them flat as detailed in last post, its time to dry fit the bottom. The bottom is built oversized. I had already marked centerlines on the bottom, as well as on the transom, the frame and the stem of the boat. So after laying the rough cut bottom atop the upside down boat, I crawled under and lined everything up. Then I came "topside," checked everything again, and tacked the boattom to the chines, transom, stem and center frame with brad nails.
Next, I traced around the bottom overhang. I sanded a pencil flat to make this line as close as possible. Then I removed the bottom and clamped it to a scrap sheet of plywood. I set my circular saw for a shallow and cut out the shape just outside my line. Then I placed it back on the boat, and used a plane and sandpaper to bring the bottom to its exact size, rounding it somwhat at the chine so it will take fiberglass cloth better.
Next, using a shop-built spacer gauge, I pre-drilled the holes in the bottom through which the 1/2" screws into the chine would go. This gauge was the designers suggestion and a good one. Another tip I got from a friend, was to "knock down" the little bumps left by the drill with sandpaper to ensure a flatter fit on the chine ( Thanks Bob!). Finally, I applied a straight coat of expoxy, followed by a thickened mixture and screwed the bottom on. Check back to see the results--I've got squeeze-out to manage!

May 20, 2009

Build a Dinghy:Part 12

Well, spring is here, and with it, yard work and two fishing boats to get into the water. Slowed my progress a bit for awhile. Got back to building and dry fit the chines.Had a problem in that I overcut the notch in the frame. You can see it in the photo. I made the depth OK, but was too wide. I used a short piece of chine as a marker to make the cut, but unfortunately, that little cut-off was thicker than teh rest of the chine. Sloppy dressing on my part. Oh, well. I'll fill it with thickened epoxy adn move on. You can also see here where the chines butt against the transom an stem. Those fits came out great. I used the technique of clamping the pieces in position and then running a saw through the joint several times to make a perfect fit. The idea comes from Greg Rossel's book, "Building Small Boats."
When I had the chines clamped in position, I drilled and countersunk for the 1/2" silicon bronze screws. The chines are glued with epoxy and screwed. (The designer calls for nails, but I chose screws for the additional control in such long skinny pieces. I countersunk them just a hair, as the plywood is only 6MM, or 1/4". Though I have drills and power drivers, I drove the screws with a manual screwdriver, loaded with the appropriate size squre drive tip--better control. Also, note how I taped the handle so as not to befoul it with epoxy.
After screwing and gluing, I cut the excess chine nearly flush to the sides with a pull saw, then a cheese grater( surform tool). Final dressing to flat was done with a low angle block plane, using a level to make sure I was flat to provide maximum gluing surface for the bottom, which goes on next.

May 5, 2009

Build a Dinghy:part 11

Business travel, spring yard chores, building docks and getting my big boat ready have taken most of my spare time. Today, I dry fit and glued the major parts together, converting a pile of wood into a boatlike object.
I used plywood pads and machine screws to assmble and test fit. The pads prevent the head of the screw from creating a bigger hole to fill later. I attached the stem at the bow, using a length of cord wrapped around the planks to bring them together. I then attached the frame. Moving aft, I used more cord to pul the planks against the transom sides. Doing so revealed that I needed to bevel the sides and bottom of the transom some more. So I dissassembled adm reassembled 2 more times, shaving the bevel with a fine set plane til I had good mating surfaces. Epoxy is great and fills gaps, but good wood to wood fits are hard to beat.
Once the fit was right , I drilled pilot holes for my permanent fasteners. I dissassembled everything again and coated the surfaces to be joined with epoxy. This soaks in to the wood, so that my subsequnet thickened mixture doesnt soak in and starve the joint. I let that gel, then I applied the thickened mixture and re-assembled everything, this time with silicon bronze ring nails (transom and frame) and silicon bronze wood screws (stem.)
It was 50-degrees F tonight. Using the fast hardener gave me about an hour to do all the gluing, reassembly and clean up of drips, spatters and squeeze out. I masked the permimeters of the joints with packing tape (epoxy doesnt stick to it) which made cleaning easier.