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Installing Fixed Windows: A Different Approach

July 2, 2019

I knew I was in for some work when I purchased my 1978 Columbia 10.7 (10.7 m/35’) “meter” boat. I didn’t realize how much until I started to replace the fixed widows in the cabin side. The window openings were simply cut through the cabin top, exposing the plywood core in the center. The plastic windows were the sealed with sealant and held in place with plastic window frames.

 That might have worked well for the first five to ten years of the boat’s life, but by the time I purchased her, the sealant had failed. Water had leaked into the plywood core, rotting it. Water had also leaked inside the boat, water staining and delaminating the plywood panels on the inside of the cabin. The windows themselves were cracked and crazed from years exposed to the sun’s UV rays and the plastic frames were history.
I would have to replace the rotted core in the cabin sides, install new windows and then replace the interior paneling. I had previously replaced the windows on my Matilda 20, using stainless steel screws and barrel bolts. Simply bolting the new windows in place would leave the fastener heads proud of the interior cabin sides, interfering with the installation of the new paneling. I could drill through the cabin sides and then through the interior paneling but that method left entirely too many possible leakage paths for my liking.
So I came up with a different approach to mounting the new windows, using one of my favorite pieces of hardware, the Tee Nut.
The first step in the process was to clean out all the rotted core plywood from between the inner and outer fiberglass skins of the cabins sides. I use a variety of tools, from saws and scrapers to chisels and a Dremel tool. Once the rotted core was removed, I filled the void with epoxy filler. The solid epoxy filler would form a waterproof plug preventing water from reaching the remaining plywood core.
I then traced the window opening onto a sheet of cardboard and used that to lay out the window opening on my sheet of plastic. The plastic comes with a protective layer of paper, ideal for laying out the window. With the window opening marked, I then drew a second line 1-1/2” outside the window opening line. This would form the overlap of the plastic on the opening and allow for fasteners. I drew the centerline for the fasteners and then spent some time laying out the exact location of the individual fasteners. I reworked the locations until I had uniform fastener spacing around the periphery of the window. Take your time here; nothing looks worse than unequal spacing between the fasteners.
After cutting out the new windows, I spent time finishing the edges of the plastic. This is important as any scratches left on the edges could form cracks in the future. I sanded the edges with progressively finer grits of sandpaper, ending up with 600-grit. I then used toothpaste to give the edges a final polish (toothpaste is a mild abrasive). The edge should be as shiny as the surface of the plastic.
I drilled out the fastener holes with a drill especially prepared for drilling plastic. A standard drill bit will “grab” and crack plastic. Use either a special bit for plastics or dull the cutting edge of a standard drill bit. The holes are dilled oversize as the plastic expands and contracts at a different rate than the fiberglass cabin sides.
I had a helper on the inside of the boat make sure the new window was properly aligned, and then I drilled all the fastener holes through the cabin walls. Now comes the interesting part. With the window again off the boat, I counterbored all the fastener holes from the inside of the boat. I used a hole saw and a spade drill bit large enough to accommodate the flange of a Tee Nut and drilled through the inner fiberglass skin and through the core but didn’t touch the outer skin.
I now bolted the new window in place. Instead of a nut, I used a Tee Nut in the recess, with the flange of the nut toward the inside of the cabin. Tee Nuts are available with various barrel lengths; make sure yours are short enough to be completely imbedded in the cabin wall. I used stainless steel Tee Nuts to avoid any future corrosion issues. After sealing the end of the Tee Nut with a small piece of tape, I then filled the recess with epoxy filler, sealing the Tee Nut in a solid epoxy plug that was flush with the inside cabin wall. Work the filler around the Tee Nut to eliminate any air pockets. The window would then be bolted in place with not one fastener penetrating the cabin wall, eliminating a vast number of potential leaks.
To finish the installation, I peeled off the band of protective paper between the outer edge and the window opening. This would be where the new window overlapped the cabin side. I roughed up the surface with 80-grit sandpaper and then painted the surface with polyurethane paint matching the color of the cabin side. This would hide any trace of sealant or fasteners under the window.
To finally fasten the window in place, I placed all the fasteners (pan head stainless steel screws and stainless steel flat washers) in their holes in the window and then placed a neoprene rubber washer on the fastener. This served two purposes; first of all, it held the fastener in place while I was trying to install the window. But more importantly, it served as a spacer for the sealant. Most sealant joints fail because they are too thin to allow for the constant expansion and contraction of the items it is trying to seal. The rubber washer provides an adequate sealant thickness; you tighten the fasteners down on the washers, not the sealant.
Before applying any sealant, I taped off the area surrounding the window and the window itself with plenty of blue masking tape. The tape contains any sealant squeeze out and make clean up a minor chore.
With a healthy bead of sealant applied to the window, I could then fasten it in place. I alternately tighten the fasteners a bit at a time to avoid over-tightening any one fastener and distorting the window. Once the fasteners were tight, it was a simple matter to scrape off the excess sealant, clean up the joint and remove the masking tape. Done carefully, there is no sealant mess and almost no clean up.
The last step was to install new ash veneer plywood paneling inside the cabin. The light ash panels made the interior light and much less like the teak cave the cabin used to be.


 

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