It is much easier to find and buy 4x8 foot plywood than a 4x16 foot. So for each boat we buy 2 pieces of 4x8x1/4 marine fir plywood, and scarf them to (almost) 16 foot length. This is quite easy to do provided you have a bit of skill with a block plane or power planer. We use the latter. Plan on an hours work per scarf for two people. We do this a couple of evenings before the actual Festival.

First you must build a "Scarfing Press", which is simply a wooden frame 50 inches wide and 10 inches high on the inside.

The press is mounted on a sawhorse. Two other sawhorses the same height are arranged 5 feet either side of the press. Call these sawhorses S1 and S2.

Two sheets of plywood are placed on sawhorse S1, and passed through the press opening. If you have AB or AC plywood, then one sheet must have the A side up, and the other must have the A side down. Draw lines 2 inches from the end of each sheet. Arrange the bottom sheet to be right at the edge of the press table, and the top sheet on the 2 inch line, step fashion. Clamp them down to the table with the clamps out of the way of the work area. Make sure the plywoods are flat, not springing up in the air, but firmly on the table and each other.

Now using a block plane or power plane set to 1/64" start feathering both ends simultaneously. Plane off wood up to but not beyond the lines. Plane until the bottom ply of each sheet has a feather edge. As you remove wood you will expose the glue lines between the plys. Those are your friend. The goal is that all glue lines are straight, and parallel to the end. If a glue line sags toward the feather edge remove more wood there. The sag will gradually straighten up.

A bit before reaching the feather edge switch from power planer to block plane. I use a little 5" block plane that fits nicely in the palm of my hand. You can also switch to a belt sander (be gentle), or an orbital sander. As you approach the finish, be less aggressive. You are done when both bottom plys have feather edges, the glue lines are straight and parallel without sags, and the removed wood just touches those two pencil lines.

Now you have two choices depending on how many sheets you are scarfing.

Unclamp the sheets. Slide the sheets back a few inches on the table and lay down a 50 inch sheet of wax paper under the presses top beam. That is your parting agent. Slide the sheets back into the press frame on top of the wax paper until the bottom scarf is exactly under the 2x6 top beam. Mix epoxy glue with thickener the consistency of mayonaise, and spread on the exposed 4 inches of scarf, both sheets.

Without disturbing the bottom sheet, remove the top sheet and flip it end-for-end. Here is where you need two people, and lots of room. The sheet you have flipped now has its glue on the bottom, and the two feathers are matched up. That is why the third sawhorse (patiently waiting all this time) is needed. Match up the two feathers. The feather of the flipped sheet should just touch whatever is left of the pencil line on the other sheet. And the joint should be right under the press beam. Double check the total 16 foot length is straight.

Now put down a second 50 inch length of wax paper covering the joint area. And on top of that put the pressure plate. Using the 4 or 5 wedgies, wedge the pressure plate downwards pressing the glue area together. The wedgies go vertically from the pressure plate to the top beam. Just bop them with your fist.

Check once again all is aligned, and straight. You have finished your scarf.

I have done up to four sheets. First do all the planing. Remove the sheets and stack them carefully to one side. Be careful not to harm the feather edges.

Then when the last pair is planed, proceed as above under "One Sheet." Flip, align, wax paper, but not pressure plate. Instead bring over a pair of planed sheets and lay them on top, carefully not disturbing the already glued pair. Spread glue, flip, align, wax paper, another pair. Don't forget that wax paper. Leave that out and you've really got a mess on your hands.

Than at the end, one more wax paper, pressure plate, wedgies, bop, bop, bop. You are done.

So some math. If you make your wedgies 8 inches long, then because of the two curves in the ends it is actually adjustable from 7 inches to 8 inches. In fact the middle of this range is practical, 7-1/4 to 7-3/4. The frame gives us 10 inches, and we used 1-1/2 for the table and the pressure plate. That leaves 8-1/2 for the plywood, and the wedgies. So an 8 inch wedgie is perfect for four sheets of 1/4 inch plywood, works fine for 3.

I also have a set of wedgies 8-1/2 long. That is perfect for one or two sheets. I would not try to do more than four sheets at once.

Happy scarfing!

Tom Gibson
February 25, 2007