Reverse order of fiberglass Layup?


I'm building a Shearwater 14 and the suggested fiberglass layup is one layer that covers the bottom and sides, one layer that just covers the bottom with a little overlap onto the sides and one layer just at the bow and stern.  Blending the various layers into eachother took quite a bit of sanding to make it all look seamless.   I was looking at the inside "floor" of the kayak where the glass cloth overlays the fiberglass tape of the puzzle joint and noticed how the transiton looked pretty good.  It got me thinking..what if I reversed the order of fiberglass cloth layup such that the bow and stern pieces were covered by the bottom piece which would be coverded by the bottom/side piece.  In this way each layer would cover the trasition of the cloth below it.  I'll have to do some experimentation but it seems like the transitions would be much smoother and possibly made invisible by subsequent fill coats, thereby eliminating lots of sanding.   Any thoughts on this?


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RE: Reverse order of fiberglass Layup?

Hi windsurfer 18, 

the advantage of doing it the original way is to ensure you have the longest pieces and dont, in your sanding, take long runs and cut them into shorter runs....which degrades the strength a tiny bit. (btw i don't take credit for this analysis, but read it in a book discussing glassing technique and why the order is the way described and not reversed)

it can also be challenging to properly fill/wet out pieces that are going over shorter pieces becuase now there are little shelfs the bigger peice has to work over when it gets to the edge of the smaller piece. bending over those little shelves are also a negative for strength - to the extent possible, you want the straightest fibre runs possible.

finally, i am not sure you would find that you would save a lot of time in sanding.   the best way to save sanding time is careful, neat, glass work and some tricks like cutting pieces to clean lines when it is plasticy vs messy work that is allowed to fully cure.

all that said, i highly encourage folks to experiment and see if there is a better mousetrap.  but there is a lot of accumulated experience on this particular point that i think explains why it is the default approach.


RE: Reverse order of fiberglass Layup?

Howard's right. The edge transitions have to be smooth or there is the chance of voids which would be the starting points for delamination or leaks, or blobs of epoxy which could float the cloth. You need to either feather the edges or fair them before applying glass that spans the transition and you have to do it for every layer where larger glass covers smaller. Whereas you can have multiple layers of smaller over larger and only need to fair once upon completion, so it's actually more work putting larger on smaller.


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