Building the Dory Tender
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We found that the 1/4" plywood was particularly hard to bend at the transom for the garboard strakes. The hull transitions very quickly between the last frame and the transom, and it was a fight. This boat would be impossible to plank, in my view, in any plywood thicker than 1/4" so please take note.
Lining things up was a major hassle, exacerbated because the overall structure was never that well fastened. You can see braces running from the legs of the sawhorse to a large timber on the floor, a batten running from the stem end to the wall, and two battens running from the top of the transom up to the edge of the bench. What we really should have done was have a plywood floor and then been able to fasten the frame ends (leaving them long, perhaps), stem and transom directly to the floor. We had a concrete floor and made do with what fate gave us. Here what I did was clamp a piece of scrap with its straight edge on the centerline of the stem and then I sighted that edge down the centerline drawn on the bottom. Crude but effective.
This is my little gee-whiz jig for laying out reference lines for beveling the edge of the bottom. The bottom edge of the jig is all in one straight line and the cutout reaches around pesky parts of the boat. By laying this on the frame edge I could transfer to the bottom the point at which the garboard would lie. We marked those points and then connected them with a batten. I also used this jig to transfer the marks in the same way from the transom and stem bevels to the bottom plank.
The most important thing about this photo is the unfairness of the plywood planking at the center frame. If you look closely to the left, amidships, you will see that the garboard plywood plank makes a hard turn at the frame. In plywood the grain direction of each veneer is at right angles to the adjacent veneer. This means that in a piece of 1/4" plywood made up of an even number of veneers, only an effective 1/8" of the material is going to have the grain running longitudinally. So this plywood is going to have a very hard time keeping a fair curve past a frame when the hull has a lot of shape (i.e. tubby). Marc and I talked about this and he thought that a high grade marine plywood would have made the difference here but I disagree. As I mentioned before, in this design increasing thickness to 3/8" plywood might have been impossible to bend in the garboard aft. What I suggested to Marc, and he has gone back and redrawn the plans, is to have batten inside the hull supporting every seam. There are a lot of advantages to this: first battens will support the plank edge, not only keeping it fair, but this will also stiffen the edge. Tom found it very tricky to place the plank edges for the next plank. The distance between the transom, stem and between frames is so great that it buckles under the plane. I also think that a batten at every seam will act as a nice clamping pad when gluing the planks at the laps. Finally, it is tough to spile the top edge of each plank because, again, there are so few reference points. Battens let in to notches in the frames will create instant ribbands that will make spiling a snap. You will lay the plywood on the boat and just trace off the shape from the battens.
The best solution I could think of for the unfairness problem was to make the dory's sheer plank out of real lumber and not plywood. I got a piece of Spanish cedar and scarfed it for Tom (note to self and other: do NOT scarf planking that will be varnished using Gorilla Glue. It leaves a light yellow line that is too visible and can't be removed. Epoxy darkens with the wood and the line will disappear with the appication of varnish or a coating of more epoxy). But the cedar plank, planed to just a hair over 1/4", faired very nicely and pulled the plank edge below it into shape. In the end the unfairness in the edge of the garboard just won't be visible with the boat right side up.
Out of sequence, but Tom's scarf joints were quick and dirty, just a pad of 1/4" plywood as a butt epoxied at the joint. You don't need a very long butt block, and if you make it too long it creates a flat spot in the plank when bending.
A boy and his boat. Here is Tom posing with the dory just minutes after she came off the strongback. This action revealed some pretty ugly globs of glue inside the hull, the result of squeeze out when hanging planks that weren't cleaned up. Tom now curses the fact that he didn't spend more time laying in the dirt and sawdust scraping the dripping epoxy (wonder why?). I don't have the heart to tell him that with bent frames, risers, knees, gunwales, thwarts and painting and varnishing all that stuff still to go, he's probably only about half way there. I hope he's not tempted to take the dory to his neighbor's swimming pool for a premature launching.
Eds note: never climb into a small boat on dry land! Easiest way there is to break it.
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Douglas Brooks
August, 2009
Douglas Brooks (www.douglasbrooksboatbuilding.com) is a boatbuilder, writer and researcher specializing in the construction of traditional wooden boats for museums and private clients. He lives with his wife Catherine in Vergennes, Vermont.
© Copyright 2009 by Douglas Brooks
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