Scaling Up S&G Offsets

Submitted by KenB on Thu, 05/17/2018 - 09:12

Thinkin' of a new project.

I've always liked the Cunningham Sea Kayaker S&G ... got the plans ages ago ... a couple of pages full of offsets. I wanna scale up the beam. So ... how do I do it?

One idea ... say I wanna add 2 inches to the max beam. This method assumes the angle of the side panel relative to the bottom panel is unchanged.

Bottom panel: Add 1 inch to the offset at the max width of the bottom panel ... take that number and use it to ratio the other bottom panel offsets.

Side panel: Widening the bottom panel lengthens the chine ... so determine the true length of the chine based on the stock offsets ... and the widened offsets ... and use those to scale up the length of the side panel.

Deck panels: Haven't thought much about it ... should be able to riddle out something similar.

I'm not averse to a little pattern making, trial and error, tweaking or whatever.

Anyone have any ideas?





mick allen

Sun, 05/20/2018 - 02:29

If you don't mind making patterns - 1)what about drawing up all the sections overlaid, 2)sending that drawing out to print to get rescaled in width, 3) making some [say 3] evenly spaced forms from those sections and aligning them temporarily, 4) stringing 2 stringers on the each side of the chines of the forms and hot gluing diagonal [or wide] spacers between so the single panel ends up looking like a trussed member.

then use that spiled member to trace on your ply. Use a heatgun to take all apart and repeat for the next panel.  That basic tech has worked for all manner of simple and complex [use more forms] shapes. And actually would be quite rapid too.

Another more simple tech is to use  wide-ish scrap panel material hot glued to each other down the centre part of each panel and then cross pieces at each form out to where the chine should be - then place on the good panel material and batten the cross pieces.  I/ve used that tech many times to great effect on highly complex shapes.

You're just changing the width so whatever offsets are given for the stem/stern forms will be fine.