: It seems to me that the pupose of running a fillet along the seams on a S&G
: kayak is to basically fill in the corner and to provide some initial
: bonding between the plywood panels.

Sounds about right. I liken this to a cast-in-place glass-reinforced-plastic chine. On older methods of boat construction a chine strip would fill the inside of each joint between panels or boards and provide a surface that the panels or boards could be nailed, screwed or glued to. Frequently the gap or joint between the chine strips and the matching panels would be sealed with a gasket made from a strip of cloth soaked in a marine glue. Fitting these strips was time consuming as the curves of the boat made the panels meet these strips at an angle -- and that angle varied along the length of the chine strip.

Some current designs use a single chine at the joint between the deck and hull, rather than use glass tape and epoxy resin. It may be easier this way, as the builder can do all the work from the outside of the boat. No need to climb inside and try to roll out resin and glass tape!

: The pupose of the fibreglass tape is to provide the strength (Is this so?).

Well, yes. But it is adding strength not to the boat, but to the adhesive properties of the joint. That is, The epoxy has a breaking strength of so many pounds per square inch of area that it covers. If you are working with 1/8 inch thick plywood (roughly 3mm) and you bond two pieces with a simple butt joint then the epoxy will contact an area 1/8th inch wide. If you now cover the top of that joint with a 1 inch wide layer of glass cloth and apply resin, then the resin is working on an area 8 times greater. Do the same on the ottom of the joint and you have your adhesive working on 16 times the original joint area. That makes an incredibly strong joint.

As a comparison, consider a typical scarf joint made by tapering the two pieces to be joined. Typically these joint are 6 to 12 times the thickness of the material. With 1/8 inch material a scarf joint that is 12 times the surface area of the glue joint would be 1.5 inches wide. We know from experience that these scarfs joints (if made with a good glue are as strong as any other spot in the wood. In fact, when made with epoxy, 1:6 scarf joints are frequently as good. (these would have gluing areas of 3/4 of an inch) By contrast, using just 1 inch tape gives an even greater gluing surface area.

Engineers will probably quibble that these are not valid direct comparisons as the forces applied to the surface bonded panels do not come at the same angles as the forces along a scarf joint, but with such thin panels as we use, and with the greater surface area of the glue joint, things tend to work in our favor. In fact, we typically use wider glass cloth, which has even more surface area, and spreads the stresses over a larger area.

: So if there is no corner to fill in (i.e. at the bow and stern ends of the
: keel to side seams and also possibly in the centre of the 2 keel panels
: where the bottom is almost flat) then, would it be better to just place
: the tape straight onto the seam without the fillet.

Yes. Exactly as described above.

: The only problem would be that the tape would be held off the panels by the
: wire stitches so I was thinking of placing short strips of tape between
: the stitches to hold the panels together then removing the stitches then
: apply the tape as usual.

The tape is pretty flexible and fits very closely to the wires. if you want to save some money and get an even more malleable material, cut your own "tape" from pieces of fiberglass cloth. Cut it at a 45 degree angle to the weave, or on the bias, and it is much easier to fit around the curved areas than tape would be.

: These are just random thoughts of someone with too much time to think and not
: enough time or money to do.

I wish I could help you with the time management, but for that I would have to charge you. As for the money, though, head over to the library and get any books you can on boat building. Then pester the librarian to get you hooked into the interlibrary loan system so you can borrow books from even more libraries.

PGJ