Rounding over or chamfering the openings (both faces) before varnishing or epoxying will protect the face veneer from snags. Varnish will (with enough coats) seal the exposed edges; epoxy will actually plasticize the wood fibers, improving them structurally. As Peter notes, a strip of light weight glass fabric or tape would be invisible if fully wetted out.
You can buy a bendable edge channel slightly less ugly than the original metal product:
http://www.trimlok.com/prod/Rubber-Lok/ ... ok_81.aspx
Many new boats are delivered with TrimLok edge channel. It is quick and easy and can be removed if/when you want to try something fancier. TrimLok has products for every application.
For a wood trim, you might find a local woodshop that will make corner pieces and straight runs for you. They may be cheaper than catalog teak. Access to a pin router makes the job faster and less scary; as a cabinetmaker, tooling small parts is one of the most dangerous things I do. And you can spend more time building jigs, templates, and safety devices than actually running the parts! That's why they are so expensive. A retired or hobby woodworker might make them less expensively than a busy professional shop.
Do you have access to certain tools, like a tablesaw or router? There are a few trim solutions you could do with simple tools, fairly safely. The easiest is to buy or make a bunch of angle (L-shape) trim; square your openings, and glue the angle onto the outside face like a picture frame. You can plane or sand away any overhang on the inside face. You lose the rounded corners, but this is the quickest approach. If you want to complicate matters a little, you could make angle with the short leg half the ply thickness, then aplly one 'frame' on each face of the ply, gluing the seam where they meet. Or, if you really want to get fancy, you can make two 'frames' out of flat material, perhaps 1cm thick. Miter the corners & round them to match the corner radius but make the inside cutout slightly smaller than the plywood opening. Glue one frame to each face of the plywood so the frames form a channel, then fill this channel with epoxy (Six10 is perfect for this.) Very strong & maintains the rounded opening. I'll post drawings of the three methods later today. All can be done with simple tools.
That is good to know, Jan. Because it appears a previous owner of Fionn hit something hard with the keel, and the aft keel-to-hull transition was sloppily repaired. Also, the cabin sole is soft at the bottom of the stairs, and the foam under the floor has gotten nasty. So I will be pestering you for advice when summer comes!:) (Now if only I could get the mast step bolts loose....)
Great drawings, I'll keep them for upcoming projects 
