Fiberglass layup for hull question

The instructions for my Shearwater say to lay up the fiberglass starting with the full hull piece, the bottom piece, then the bow & stern reinforcements. I'm considering doing the opposite-starting with the small pieces, and covering all with the full piece. Has anyone here done it that way? The reason I'm thinking of this is because although I get good resullts cutting my 'glass with a pinking shear, I'm wondering if little shreds of 'glass will try to pull off the ends of the exposed smaller pieces, and drive me crazy.

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RE: Fiberglass layup for hull question

I've never tried the 'opposite' way but doing the small pieces 2nd is no big deal. Yes you have  a little shredding if you're not careful but it is manageable and it all feathers in quite nicely with a ROS.

RE: Fiberglass layup for hull question

I wondered the same thing, and ultimately chose not to mess with the recommended method. (For the record, I'm just finishing up my 2nd SW Hybrid.) 2 reasons I can think of:

1. Putting down the smaller pieces first may cause the final (biggest) layer to have air pockets along the edges of the smaller pieces. You can probably overcome this when wetting out the hull, but trying to manage the process is grueling enough already.

2. The loose threads are annoying, and look like crap at first, but they sand out pretty easily and completely disappear as you fill/sand.

3. OK, 1 more thing. I figured that CLC specifies this method for good reasons, and maybe I shouldn't second guess them.



RE: Fiberglass layup for hull question

in addition, cut your small pieces on the 45 deg. bias and you'll have little trouble with the threads or getting the glass to conform to the curves of the hull. It's very simple really.

RE: Fiberglass layup for hull question

There actually is a reason to put the full piece on first and layer the progressively smaller pieces on top despite the fact that it seems to make sense to do it in reverse order.  When you layer the fiberglass pieces, you end up with a very small lump/ridge along each of the edges of the smaller pieces.  When you do the final sanding, you want a smooth boat so you sand the ridge out. 

If the smaller pieces are underneath, the only way to get it smooth is to sand through the top (full) layer of fiberglass which decreases the structural integirty of the glass (you've just created a line of weakness with no continuous filaments).  If the smaller pieces are on top, you are just sanding away the edges of those pieces of cloth so it doesn't compromise the strength.  

Hope this helps,



RE: Fiberglass layup for hull question

Kathy, great response!

RE: Fiberglass layup for hull question

Thanks for these very good answers, especially Kathy. I hadn't thought of that.

RE: Fiberglass layup for hull question

FWIW, the ridge lines can also be eliminated with fairing compound and sanding. Either the commercially available premixed compounds or a stiff mixture of phenolic micorballoons and epoxy will work fine. This is only good for painted areas (unless you really like the look of purple streaks on a varnished hull), so go with Kathy for varnished areas.

In addition to Kathy's well-taken points about preserving the integrity of the glass, even if the ridge lines are removed, internally there will be a line of epoxy with less glass in it than the surrounding areas. Technically this adds useless weight and can form a stress concentrator. As a practical matter, for the boats sold here it probably won't even be noticeable, just mentioning it for completeness.

Finally, loose threads can be completely avoided by outlining the area to be cut with tape (I use blue masking tape for visibility, others use clear packing tape). Make the outline a bit larger than the required final size of the glass. Cut the glass down the center of the tape and there will be no loose threads to form glass snot during the layup. Once the epoxy's cured to the "green" stage (leathery, slightly tacky) cut away the taped area with a razor blade and push the edge down with a gloved finger or similar tool. No loose threads.

Have fun,



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