Is this "bottom piece" an extra layer on the bottom? -then place it on the boat first, add the full layer (all dry still), and wet out the two layers together.

you can add little stem glass pieces over the main glass, but there will be sanding involved to clean the edges.

It is tricky to cut fiberglass without ending up with loose fibers.  I've had the best luck using a roller cutter (can find it at a fabric store - quilters use it to accurately cut fabric for quilts).  However, you will still end up with some loose fibers once you dry brush it as you found out.  Just do the best you can, snipping the worst of the loose fibers before you wet it out. If you lightly sand or scrape (use a cabinet scraper) the remaining bumps before the resin gets too hard it's noo too onerous.

You do need to put the full glass layer on first, so it it is underneath the partial bottom piece.  If you put the partial piece underneath the full piece, when you sand the hull at the end you will risk cutting the fibers in the overlying full piece at the resulting small ridge, which will compromise the strength of the fiberglass. 

You can add the stem strips after wetting out the other two layers if it's easier.  Less risk of things moving around as you've noticed. Just lay them on carefully because once they contact the underlying wet resin they will stick and you can mess up the underlying layers if you try to pull the stem strip off to re-position. 

Easiset way to avoid loose threads - cut the piece a bit large, say an inch or so, but before cutting cover the cut line with masking tape. Cut down the center of the tape and there'll be no loose threads from either piece.

Once you've wet it out and it's cured to the green stage - non-tacky but stiff like leather or rawhide and still sticky when you push hard - use a razor to trim it to the final size (which gets rid of the tape). If this leaves a bit of raised glass, push it down hard and rub it with a gloved finger. That will make it stick to the bottom layer with almost no ridge. It may need a trivial amount of sanding or scraping when it's cured, but that would be like a light touch with a sander or a couple of swipes with a scraper. Nothing major.

Been doing this for over a decade, no thread runs or snotballs in all that time.

Have fun,

Laszlo

Thanks for your ideas - I thought there had to be some better ways than the mess I made!

Joel

Laszlo, as you spread and work the glass cloth to tightly conform to the curved surfaces of the hull, I would think puckers would likely form near the edges that are taped. No?

Old Yeller 

Not if you cut it larger than the final shape. The extra cloth provides the material for the curve to take up. On really extreme 3D curves the margin may have to be larger than 1", but CLC boats all have nice smooth curves.

Laszlo