Stitch and glue building is the name given to boat building using plywood sheets held together by copper wire, string, cable ties, or some other method. The joint is then glassed over – on larger boats the copper wire may be left in, but on smaller craft it is usually cut out. An epoxy fillet joint is usually made on the inside of the joint on smaller boats, and the outside is taped over with fiberglass tape. On larger boats both sides of the joint are usually coated with fiberglass tape epoxied over the joint. The method provides for a very strong joint without the need to cut chine logs or other difficult to shape rabbets.
Here’s a brief overview of the process:
First, you’ll need to cut out the plywood and drill holes along the sides to be joined together. In general, the holes will be three to five inches apart, although in some cases you might make the separation a little wider. Depending on the thickness of the plywood, the holes will be quarter inch to one inch in from the edge of the plywood. The hole diameter should be just large enough to take the copper wire or cable tie. When you buy a kit, the plywood is precut and predrilled in most cases, cutting down on the amount of work that you need to do.
When all the wood is cut and drilled lay it out in a suitable area with the edges to be joined next to each other. Check that the pieces are laid out properly and that the holes are aligned. Check the hole alignment a second time. It is a real pain to have to undo all the ties and redo them because you misaligned the first hole. With thinner plywood pieces there is no need to bevel the edges to get a good fit, but with thickness over 3/16” many builders find that they get a better fit if the edges are beveled.
Join the plywood by passing a length of copper wire or a cable tie through the holes in the plywood and either twisting the copper wire to pull the plywood sheets together or pull a plastic cable tie tight and snip off the end. As you work the boat will start to form the correct shape, but it will be quite wobbly.
At this point you have a couple of options. You can mix a little epoxy and thicken it with glue powder or cabosil. Pull the hull to the shape that you want and glue the parts together with a small glob of epoxy. Don’t use a big glob, if you have misaligned anything you want to be able to break the joint and realign the panels. The other option is to continue wiring the panels together and just let it wobble.
Once all the panels are wired, you will want to start epoxying the pieces together. Some builders find it best to apply small globs of epoxy across the joint to hold everything tightly in place before they tape the seams together along the joints. Another way to work is to cut short pieces of fiberglass and tape them in place between the wires or cable ties. As you start to tie the panels together with tape, the entire hill will become stiffer and fixed in shape. When the fiberglass tape is set hard, you can either cut the cable ties or copper wire and remove it, or you can leave the ties in place and glass over them. Most people remove them entirely and with the boat held together with tape the final glass work can start.
To do the fiberglass work, make up a mixture of epoxy and brush it onto a seam. Lay the fiberglass tape over the epoxy and then brush another layer of epoxy over it until the entire surface is wetted out. Some builders use a plastic squeegee to squeeze out excess epoxy, although that is not necessary. Let the epoxy set up hard over at least a 24 hour period before you continue taping until all the seams are fully taped. When taping, try to make the seams as smooth as possible or you may have to grind off fiberglass when you are smoothing the hull.
With the entire hull taped, the next stage is to make fillet joints around the interior of the hull. With the interior filleted, the exterior taped, the next stage is to make sure the hull exterior is smooth. If the hull is not smoothly taped, you will have to apply layers of epoxy thickened with filler. If the hull is smoothly taped you may want to coat your entire hull with fiberglass or simply smooth the seams before applying epoxy sealer.
The epoxy needs to be thickened to the consistency of peanut butter and applied to the hull to make it smooth. Build up the layers by applying thin coats of well-mixed epoxy. Let the layers dry and smooth them before applying more epoxy. With the hull smooth you will need to apply an epoxy sealer. Smooth the sealer with 120 to 150 grit sandpaper and apply a primer coat. At this stage many builders finish the interior of the boat before applying a top coat. If you decide to finish the exterior, sand the primer coat with 320 to 400 grit sand paper and apply the top coat.
When finishing the boat’s interior, you will need to make allowances for the fillet joint in the interior corners and will need to make new fillets for any interior frames or structure. If your fillet work is done neatly, you can usually finish the interior with a sealer or with a layer of epoxy, brushed on, or coated with a layer or two of polyurethane varnish.
Roger Marshall is the North American Editor for the Yacht Report, former Technical Editor for Soundings, and a Director and the immediate past President of Boating Writers International.