:. . . needless to say no epoxy was used
: just nails. It has steam bent oak ribs and cedar strip planking.

: The customer wants me to epoxy-fiberglass the hull to make it watertight.
: there are large cracks between the very dry planks and some gouges and
: rot. I will need to fill (with thickened epoxy) the cracks etc before
: glassing.

If the gaps between the planks are about 1/16th inch or larger it sounds like they were left there on purpose. Frequently joints would be caulked, or sealed with a fibrous material like cotton or oakum before being painted. The caulking material was somewhat flexible and compressible. As the boards would swell from absorbing water, they would pinch this caulking even more tightly, providing a clamplike seal along the joint. It worked fine as long as the boat stayed wet. When the boat would be pulled from the water for winter storage the boards would shrink back, so recaulking joints was a regular maintenance task.

Regardless of their origin, why not use thin strips of wood to fill these gaps, instead of using thickened epoxy?

I'm thinking that the thickened epoxy is going to be rather translucent, and you'll have some long gaps that will be distracting.

You could probably clamp a board parallel to the gap and use it as a guide. Then run a router, or a Dremel mototool along the gap to square it up. An 1/8 inch, or 3/16th bit should give you a nice straight-edged slot that you can tap thin cedar strips into. Sand them flush and it should look beautiful when you coat with the epoxy and glass cloth. No need to use very long strips, so you can probably use up a lot of scraps. If you cut the strips with a slight taper they will fit into your routed slots like corks in a bottle. A couple spots of glue and tap them in with a mallet. No clamps needed!

: The question is, should I seal the entire boat-hull with epoxy inside and out
: or is varnish inside sufficient to keep the wood from absorbing water?

I second the idea of just using the glass on the outside. You probably only need 4 ounce cloth as it is just going to serve as minor ding protection. You do have to use epoxy on both sides of the wood. Epoxy on the outside and just varnish on the inside is a recipe for problems.

The idea of using a penetrating epoxy sealant on the inside sounds good. Regular epoxy should soak in, but the sealant is a thinner material and it might soak in better. If it works right it will soak in and completely seal the wood against moisture. I'm concerned though, that the wood was already been finished years ago (and probably refinished amny times) and the previous finish might hamper the absorption of this epoxy sealer.. If that is the case then it won't soak in very deeply, and you'll have to rely on whatever is on the surface to provide the necessary protection, so try not to sand completely through this coating later on. Fisnish with varnish for the UV protection, inside and out, unless the outside is going to be painted.

: Any other suggestions?

I'm guessing that the strips on this boat were somewhat wider than the 3/4 inch ones we currently use. This may sound like exta work, but if you are planning to take measurements from the hull, why not measure the width of each of the strips at 2 foot intervals. Some of the strips may be long rectangles, but I'm guessing a lot of them had to be fitted into curved spaces. Im sure there are more strips than panels on a stitch and glue design of a similar size, but the concept of copying the shape of each part is the same. Pop the numbers in a spreadsheet and you should be able to practically redraw and cut any part on that boat.

Good luck with the project. Post a few pictures when you get a chance.
PGJ