Worked on our Alcort Sunfish ZIP's hull, prepping the puncture area for a Letterbox repair. I wasn't sure why it is called letterbox but it appears that this is the type of repair that would have been done to a door that had a mail slot cut into it, a way to repair that slot. Maybe we add 2 mail slots to ZIP and we're finished!
We marked the repair area so that we cut out lines that were parallel and had rounded ends. The goal was to cut away the damaged plywood and as little more as possible past that. We looked around the Carriage House for objects that were about the same width as the puncture and also for objects that had the end circumference that we needed. The items we found were a THIXO tube, a square and a roll of waxed thread. Here's the rough trim before we shaped the ends.
Used the THIXO tube to mark the parallel sides with Sharpie.
Scribed the circumference.
The long repair was about the width of the metal square. The waxed thread roll was used to scribe circumference.
We used the jigsaw to trim away broken bits, cut to the line on the sides and cut just a little shy on the ends. Then we used the Kobalt diamond file to get the final shape on the ends.
Letterbox repair video: https://youtu.be/T82Y48dKooc
Next we needed to plane down some 1/2 inch marine ply to make it 17/64th inches, put it through 12 passes on the DeWalt tabletop planer and used the Dust Deputy to collect the sawdust. Normally for solid wood we'd plane both sides, alternating sides on each pass, but for plywood we kept the good face down and planed only one side, as we knew we'd go through the veneer ply and some glue along the way.
Compared the planed plywood thickness to ZIP's hull thickness.
We made the internal backer plates about an inch wider all around the letterbox patch, marked the hull then transferred those marks to the repair plywood. Our found shop object to mark the 1 inch was our 2 foot level, it is about an inch wide.
The X marks which line to cut.
Repair backer plates cut out, they will be epoxied to the inside of the hull.
We cut 2 of each for the backer plates, and then put one inside the hull to trace the shape of the hole.
One piece of plywood will be trimmed to letterbox patch shape. All of our clamps are named for family and friends, my brother Kirk's clamp held the backer plate in place while we worked on shaping the letterbox patch for the smaller hole.
We cut out the letterbox patch with a jigsaw, to the line on the sides and left the ends a bit proud. Then we used the diamond file to sneak up on the fit of the ends. We do not want the fit to be super tight, as we want a little space around the perimeter to be filled with the thickened epoxy.
Two backer plates and one letterbox patch ready to go, one more letterbox to be cut out and trimmed to shape.
Log of ZIP.
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