We cut out the plug from 1/4 inch thick AB marine grade plywood. The masking tape was used to make the pattern, and we cut the plug a little big so we could sand fit it to final shape on ZIP.
The backer plate had to be cut into 4 pieces to fit around the internal stringer and frame.
We used TotalBoat THIXO Wood to fasten the backer plates to the inside of the hull. THIXO is a 2 part thickened epoxy and hardener that comes in a caulk tube and mixes in the mixing tip. A 18:1 High Thrust caulk gun makes disoensing the product easier.
Lots of clamps with light clamp pressure until a small bit of epoxy squeezeout is seen. Too much clamp pressure can squeeze all of the adhesive out of the joint.
Even though it is a different piece of plywood, we are trying to keep the grain running the same direction on the patch as the it is on the deck. We marked the grain on ZIP onto a sheet of poly, then moved the poly over to the plywood sheet to align the blue tape pattern with the grain on the plywood where we would cut the plug from.
Skipper's new DeWALT 24V XR cordless jig saw, wow it is nice! More on that tool later.
We cut the plug just a little outside the pattern line so we can do the final shaping on the boat.
Pulled the screws and washers from our 1953 Alcort Sunfish ZIP. Mixed TotalBoat THIXO Wood, a thickened epoxy adhesive through the mixing tube and dispensed it into a syringe, then filled the screw holes with the THIXO. Also built up a few low spots around the repair area with THIXO, we'll sand that and do a light fairing over the area with TotalFair. We don't want it too smooth, we want the area to retain its wood grain satin finish characteristic vs be smooth and shiny like gelcoat.
THIXO Wood 2 part resin and hardener flowing through the mixing tube.
Filled the screw holes so that ZIP won't have a subsonic whistle. Supersonic whistling okay.
Filled in a few low spots with THIXO, but not too much. We'll sand that and the fair it just a bit with TotalFair fairing compound, but work to retain as much wood grain as we can. Might even mold some in.
Held the backer plate in position with deck screws and fender washers. The washers keep the screws from pulling through the deck as the backer plate is pulled tight.
Pulled the letterbox plug tight with a deck screw and fender washer.
Used some cord to pull the backer patch tight until screws were installed.
We'll let the THIXO dry for 24 hours, then remove the screws and fill the screw holes with more THIXO.
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.
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.
