And Glue

Here is the answer to the second half of the question "Why is it called stitch and glue boat building?"

Gluing is applying epoxy and fiberglass to the inside joints after the boat panels are stitched together.

After stitching the boat panels together with wire, boat plans typically call for temporary spreaders to spread the side panels and achieve the boat's final shape.



Spreaders in Sea Scull hull

I have two spreaders in this boat. One is midship, to produce the widest beam possible without creating rocker in the bottom panel. It turns out that the widest beam possible is 40 inches. The other spreader is to simulate the transom since I am ready to glue but have not installed the transom.







Epoxy thickened for gluing 

The glue is epoxy thickened with silica and wood flour. I add enough silica and wood flour for the mixture to have the same consistency and flavor as peanut butter.










Kitchen spatula for rounding thickened
epoxy

I start by applying the thickened epoxy on the inside of the joints. I gob the epoxy into the joint then smooth it with the round edge of a kitchen spatula, creating a fillet. Anything rounded will work. I have used pieces of scrap wood with round ends when I could not find a spatula or stir stick with the desired radius.

Filleted epoxy



Epoxy-saturated fiberglass tape over fillets

Then I apply epoxy-saturated fiberglass tape over the epoxy fillets. The tape extends out onto the bottom panel and up the side panel, beyond the fillet.

Smaller boats use 9-ounce fiberglass tape. Such lightweight tape can be installed using the dry method (stop drinking, apply dry tape to the joint, saturate the tape with unthickened epoxy, start drinking).

3-foot segments of saturated biaxial tape

I used 17-ounce biaxial tape on this boat. Such heavy tape is difficult to saturate once it is applied to the surface. So, with the heavy tape, I installed it using the wet method (start drinking, saturate the tape with unthickened epoxy, apply wet tape to the joint, stop drinking).

One of the challenges with the wet method is handling the fiberglass after it is saturated with epoxy. When I built the Nemah, I saturated 15-foot lengths of 17-ounce biaxial tape. In order to fit the 15-foot length of tape on the work bench for saturating, I would saturate a few feet of tape, roll the saturated portion, saturate a few more feet of tape, roll some more, so on and so forth. It took so long that the epoxy began to kick-off (cure) before the tape was applied to the boat. I could feel the heat from the curing.

For the Sea Scull, I decided to install the tape in 3-foot segments. I filleted 3½ feet of the joint, saturated and installed 3 feet of biaxial tape, filleted 3½ more feet of the joint, saturated and installed 3 feet of biaxial tape, so on and so forth.

Always using small batches of epoxy.

I use my fingers to smoosh the tape to the surface and sqeeze out all air bubbles.

I stopped short of the transom and will finish gluing the stern when the transom is installed.

Gluing is easier said than done. If you use a blushing epoxy, it is best to complete the entire boat in one session with no epoxy curing between the fillet and the tape applications. This can make for a long day but it avoids sanding of the fillet.

If blushing epoxy is used for the fillet and the fillet is allowed to cure before applying the tape, a wax will form on the surface of the fillet. The tape will not stick to the wax so the wax must be sanded off before applying the tape.

Sanding cured epoxy in a convex surface is more painful than hitting your thumb with a hammer.

So, either glue the entire boat in one session or use non-blushing epoxy.

That's it. Gluing a stitch and glue boat.