one spring back formula

Posted by BobE on May 25, 2005

I've seen others, but here is one I found quickly:

I found the formulas too accurate for the materials and shapes involved with the hatches and guessed at the radius to use for the assembly jigs. I have two 3mm decks with flush hatches. Both kayaks have 16” forward decks, though the dimension of each hatch is larger than standard. Aft decks are 48” and 60”. Hatches are made from double 3mm. All three assembly jigs are made to a tighter radius – 15”, 47”, and 58” respectively. My brother Dave built similar jigs for his 4mm boats. They all experienced a bit of spring back compensated for by the jig.

The difference in radius between 58” & 60” is small and could well be deflected by your latching mechanism. Some folks have used heat and creative pressure to remove warps created by the jig or even the grain of the plywood. Dave learned an 8mm hatch is plenty strong to handle the tension from Moby latch bungies without add-on ribs.

Leave the additional layer long toward the sheers to have additional clamping room on the jig. Keeps ‘em from flattening out at the edges. The seal may take a little time to compress enough for the hatch to be flush or you can experiment with thinner foam.

In Response to: Re: spring back of flush by George K on May 25, 2005


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