> For us novices out there...could I have that in layman terms? When you say
> 1/4" radius, should the joint stick out at least that much?

No, I think he means you need to remove hull (or deck) material so that the 'sharp' edge is rounded off such that a 1/2" diameter ball set 'inside' the corner would be tangential to the planar surfaces, and a part of its circumference would form the rounded corner.

With strips you can spread the curve even wider. With 4mm marine grade plywood you have the full 1mm top layer to work with plus the gap itself which is filled with stuff. With luan plywood the top layer is very thin, maybe too thin to sand at all, so you might be stuck there with what you can get out of the gap fill material.

"Smoother "is" better, or not? "

Smoother is better, yes. The wood is already smooth, hopefully, and you want the glass to lie flat right against it everywhere, with no lifting in wrinkles or bulges. The factory pros use vacuum bagging partly for this reason. You approach the higher, desired, glass-to-epoxy ratio in the end product.

The glass doesn't want to crease (and you probably don't want to crease it, even if you can) over the sharp edge, so unless it's forced down it will hold itself off the wood surface on one or both sides. This manifests itself by bulging or slackness. If nothing is done about this, then the epoxy ends up filling in beneath the bulges and holds the cloth away from the surface. Then, when you come around to sand, you either cut through the cloth where it's high to get down to the flat wood surface, or you have to add more epoxy to fill in the low spots, and that makes the boat heavier.

Sometimes you can hold the cloth tight with tape or clamps or clothespins. Fiberglass doesn't act like normal fabrics when stretching it tight, so this can be a little tricky; it's like you are pulling on the individual threads, as they can slip by each other.

The rounder the edge, then, the better the glass can be conformed to, AND LAY FLAT AGAINST, the wood surface.