To determine the rib lengths for a new kayak replica I start by slicing up some 1/8 thick bending oak and then steam bend the thin strips under the keel by eye. The secret here is to just keep cutting and bending and not overthink things. The whole operation should take about 20 minutes.
Next I clamp the stringers on and spend about 2 hours checking the actual kayak against the drawing with various measuring devices. This is tricky because I have to mentally compensate for the rib collapse in the museum kayak and also how much the ribs will shrink and change shape during the build. It’s not an exact science but I do my best.
Next I remove and measure the test rib lengths and also measure the kayak width at each rib location and subtract that number from the rib length. Next I take those measurements and try to determine if there is any mathematical relationship between them that I can exploit to create “a rib measuring stick” that I can use to find the rib lengths in the future without resorting to exact length measurements. Not only does this make the building process easier, it becomes easier to scale the kayak, the system is more tolerant of errors in the deck shape, I can move ribs if needed, and the hull shape is fairer.
Today I finally cracked the measuring formula for this kayak which is a HUGE win. This kayak was the last ‘non-formula’ boat in our lineup (meaning students got fixed rib lengths) so I’m stoked that we are free of that now.
Next I bend in a set of full thickness ribs without the keel on to proof my rib measuring stick concept, and then it’s back to the dividers, calipers, protractors, and tape measures for a couple hours to check everything again. After noting any errors I will change the measuring stick, cut new ribs and repeat the whole process as many times as necessary.
When I’m done I’ll have a system that lets me cut, measure, and bend in ribs for this kayak design in less than 2 hours.
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