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Adjustable ribs in action

Posted by Sandy 
Adjustable ribs in action
February 08, 2021 01:59PM
I've talked a lot about using "adjustable ribs" in the boat design process. Software and model making are part of the process too but they only get you so far. To nail down gnat's ass dimensions you have to work full size. You do have to make a few educated guesses about side panel length, and height, but after that you can totally wing it with adjustable ribs. I fiddle with widths and side angles until it looks right. And then I call it a boat. I usually build a male mold first, out of cheap construction plywood, and then build the finish boat on top of that. But male molds are not a requirement.



FWIW It is possible to design carefully in something like Sketchup, using even increment dimensions at carefully chosen locations, and then blow that up into full size. And then build with plywood. But no matter how good it looks on a computer screen you never really know exactly what you are going to get until you make a full size version. And for me I need the ability to make last step full size adjustments. For any kind of dory building adjustable ribs just what the doctor ordered. You get to have your 3D cake almost the way you want it, and then to perfect it with minor adjustments. And then eat it too.
Re: Adjustable ribs in action
February 12, 2021 02:54AM
Whats going on with the sliding mechanism? Route a channel in one side then screw a strip of wood in it's mate?
Re: Adjustable ribs in action
February 12, 2021 01:15PM
Yes rout or table-saw-slot a channel on both sides, 3/8" deep for a 3/4" inch spline. That spline can free float in the channel.

Then you can slide the bottom in and out to adjust width while still keeping it all in a straight line.

Keeping an even angle on the sides almost happens automatically, once both sides are (temporarily) fastened, at each rib with two drywall screws, one down near the chine and another up high, in a spot that will likely get covered by a gunwale in a much later step.

Those angles will need fine adjustment at some point, to guarantee they are the same on both sides. I made a 24" inch bevel square out of oak 1x4. I've had it for over 30 years now.
Re: Adjustable ribs in action
February 12, 2021 02:50PM
Ah. Another tid bit. You want the rib on the left side to be the same distance from either end as the rib on the other side. So on one side but not both you need an extra 3/4" inch spacer at the hinged bolt spot near the chine. I don't have a picture of that. I haven't been in the shop in two weeks. It was 19 below zero this morning.

I do have heat out there. I'm just retired. Taking it easy. Writing code. Tying flies. I'll make that picture today. If I remember.
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