Kingfisher Drift Boat Build: Scarfing the Side Panels

The next step for the Kingfisher build is to make one 3/8″ x 4′ x 18′ long plywood panel out of 2 sheets of 3/8″ x 4′ x 8′ and one piece of 4′ wide x 2′ long. You do this by “Scarfing” the two panels together. It can be described simply as joining two pieces of plywood to make them longer. This is done by beveling two ends of the plywood in the 4′ dimension to roughly a 7 to 1 ratio. This means that the length of the bevel will be 7 times the thickness of the plywood. In my case the sides are constructed with 3/8″ Okoume Mahogany Plywood, so the length of the scarf will be 3″.

Getting Prepared

To do this I’ll need to gather up and prepare the following items:

  • Two sheets of 3/8″ x 4′ x 8′ Okoume Plywood. Check!
  • One sheet of 3/8″ x 4′ x 2′ Okoume Plywood. Check!
  • I’ll need to prepare a working surface/table to work on the scarfing and epoxying process. Check!
  • One sheet of 3/4″ x 4′ x 8′ plywood to use as a sacrificial sheet. Check!
  • Screw gun and some 1 1/4″ screws. Check!
  • 4 foot straight edge. Check!
  • I’ll need a sharp block plane or low angle jack plane. Got both and they’re sharp. Check!
  • 12″ straight edge. Check!
  • I’ll use my 4″ x 24″ belt sander to rough in the scarf joint. Check!
  • 80 grit and 100 grit sanding belts for the 4″ x 24″ belt sander! Final Check!

I’ve got everything I need.

Scarfing the Panels

Table BlocksI’m going to use the 5′ x 16′ table I assembled to do the scarfing procedure. I built the table to be 24″ tall and also built plywood blocks out of scrap so I can raise the table to 34″.

To do the scarfing I’m going to raise the table to 34″. I’ve raised it and it is solid as can be.

Preparing the Okoume Plywood to be Scarfed

Lining Up the Edge 2First I’ll place my sacrificial piece of 3/4″ plywood on my 34″ tall table.

1st Sheet Lined UpNext I’ll take one sheet of the 3/8″ Okoume plywood and lay it on top of the sacrificial sheet. I’ll make sure the long edges are aligned perfectly and I’ll match the end of the Okoume plywood exactly with the sacrificial sheet. The Okoume should be on top of the sacrificial sheet and aligned with one edge and one end.

Line MarkedMarking the scarf line. Next I’ll measure 3″ from the aligned 4 foot edge and mark it. I’ll draw a line across the sheet in the 4 foot axis.

Adding the second sheet. Next I’ll place the second sheet of 3/8″ of Okoume plywood on top of the first sheet. I’ll align the same edged as the previous sheet and line the 4′ axis up to the line I’ve drawn 3″ from the end of the 1st sheet.

As a note: The side that faces up will not be the side be up when you glue it up. This sheet will be flipped over. If you are grain matching the matching side will be facing down.

I’ll make sure everything is aligned properly and then place a couple of screws along the long edges of the sheets. These screws want to go though both 3/8″ Okoume plywood sheets and into the sacrificial sheet to hold everything flat.

Next I’ll mark and draw a line 3″ back from the 4′ axis of the second Okoume plywood sheet.

2nd LineNow I need to make sure the sheets are laying perfectly flat and are tight to each other. If not, I may need to clamp a scrap piece of wood across the sheets.

If necessary this wood piece must be held far enough back from the 3″ scarf line to work on the scarf. I’ll check it with the straight edge.

The second sheet piece will have to be screwed down through the two sheets of Okoume plywood and also into the sacrificial sheet to hold it in place during the scarfing procedure.

Scarfing the Panels

Sanding the ScarfNow it’s time to let the sawdust fly. Turn on the air filter. Turn on the fan. Put on the dust mask and get after it.

I’ll put on an 80 grit belt on my belt sander and start working across, back and forth to start taking off the wood between the pencil marks and the ends of the Okoume plywood. Creating the bevel.  The bevel will end up being about 6 inches long because I’m beveling two sheets at once.

As I work down through the layers the interior plies of the wood will start to reveal themselves in straight lines. I’ll use these lines as a reference to keep the bevels straight.

When I get close to the pencil lines I’ll have to slow down and start checking the bevel with a straight edge. The bevel needs to be straight and uniform.

As I get close I’ll transition to my block or jack plane to finish the bevel.

When the bevel gets close to “feathering out at the edge of the sheets I’ll switch to a flat block of wood with sandpaper to remove any final high spots. Do the final fine tuning by hand.

The scarf should look straight , be flat and when checking it with the straight edge it should be flat in all directions.

This needs to be as perfect as possible as the better the scarf the stronger the joint.

Adding 3mil PlasticDone with the scarfing. Here’s a photo of the sheets laid out on the table.

The sheet on the left will get flipped over and epoxied to the sheet on the right.