: My three biggest concerns are leaks, scratches, and overall
: strength of the kayak.

: I had an idea that might help address all of these concerns. I'm
: still laying the strips for the kayak I'm making. What if I
: install a plastic window when I'm done the strips, and then put
: one big piece of fiberglass over the hull, including the window?
: That should prevent any leaks, help prevent major scratches, and
: improve the strength.

Ignore the worry about scratches on the outside of the boat. Water fills them in and they are invisible when wet. Keep the inside free of scratches by covering it with a clean towel when not in use, and take care brushing out sand which gets tracked in.

fiberglassing over the plastic window is a waste of time. It won't solve leak problems or scratching, and it won't be clear enough. It wil also cost you more time and oney for the wasted materials.

Get lucite, plexiglas or other acrylic glazing materials from your local hardware store or supercenter. You can cut it yourself, or have them cut it to size. one or two pieces should do. A 20" by 20" piece can be cut in half to give you 2 10" x 20" windows--one for each side of the hull. That way you can keep your center strip or three strips, to keep the keel area of the boat strong and continuous. Put the window areas on either side of the keel.

You will put the window plastic in place just like you install a deck hatch. Put a lip on the inside of the hull, After the boat has been glassed, add something for a gasket, place the plastic over the lip and screw it down, or glue it in with a marine bedding compound like 3M's 5200. Don't expect the plastic to bend. plan to put the windows on flat areas of the hull. by not bending the plastic over the keel you should be able to find relatively flat areas on either side. If you use closely spaced bronze or stainless steel bolts to hold the window tight against the gasket you'll be able to replace the plastic every few years when it gets too scratched. You'll probably want to pull it out when sanding the boat, too.

If it leaks, redo the gasket. Or live with it. At a depth of less than 6 inches, the water pressure on the gasket is going to be less than 1/4 psi, which is pretty easy to deal with.
A bead of household caulk would do well. so would a strip of closed cell foam insulation. Cut the ends at a long angle and overlap them.When you tighten down the window the pressure will pull the joint tight together and keep out leaks.

: I've never fiber glasses before. Do you think it would adhere to
: the plastic? Would the fiberglass be likely to crack at the
: transition between the wood and plastic? I know that when you
: put the fiberglass over wood you basically can't see it. It is
: clear and you can see through it to the wood. I assume
: fiberglass on plastic would also be clear, but would it distort
: the view too much?

Definitely give you way too much distortion. It looks clear on wood because it is sitting right on top of the wood.

: What do you think?

I think the first postings I did on this list back in the early to mid 1990s were on this topic. Might want to check the archives for some (really) older posts on this topic. it keeps coming up.

Hope this helps

PGJ