This step is necessary, because the lines of the boat as shown on the plans, which I'd drawn out full-size, define the shape of the outside of the hull. The frames (or, colloquially, "ribs") of the boat, however, lie on the inside of the hull planking, and hold it all together. I therefore had to subtract the 1-1/4" thick planking before I could accurately build the frames.
But really, it's more complicated than that.
If the hull did not taper in the fore-and-aft direction (that is, if it were a rectangle as viewed from above) then applying the correction would be a simple matter of subtracting 1-1/4 inches from every cross-sectional slice on the lines drawing, and making the frame. In real life, however, the boat tapers from a point at the bow, broadening amidships until frame 14, then narrowing again from frame 15 to the stern. The magnitude of the deduction varies accordingly - at the bow, where the hull converges sharply, the 1-1/4 inch thick planking is laid on at such an angle that, when viewed in cross-section, the planks are almost 2-1/4 inches wide. Conversely, at frame 14, the angle of the planking is nearly zero, and the cross-sectional thickness of the planks is approximately the same as their nominal thickness.
But really, it's more complicated than that.
The above discussion neglects the fact that in addition to changing along the length of the boat, the angle of the planking also changes vertically along each frame section. It's not enough to compute a planking angle for every 24 frame sections. I had to compute fourteen planking angles (from the very bottom of the keel up to the top of the deck sheer) for every 24 sections, then convert them to thickness deductions, and then interpolate between them (using the flexible batten in the photo above) to define the shape of each finished frame.
It was boring and tedious and I hated it, but I got it done, and just in time, for no sooner had I done so than the temperatures plummeted and winter arrived for real:
So in January, I retreated indoors and used the deducted lines from the plastic in the top photo sheeting to create plywood patterns for each frame, like the seven shown here:
Then in February, I took nine Black Locust flitches that Dad, my friend Selwyn, and I had sawn out previously, planed them to thickness, and made two complete frame pairs out of them:
That wood had been seasoning for years, and I'd intended to use it to frame the entire boat. There was only one problem - until now, I'd had no idea exactly how much I would need. The boat contains 24 frame pairs. I'd just made two of them, and used nine flitches to do so. There were around 21 flitches left.
I didn't have nearly enough.
