dealers, and technicians on methods and materials for
replacing the acrylic glazing. One suggested polyurethane, such as 3M
5200. The technical data sheet on any of the 3M polyurethane products
specifically recommends against using these products for glazing without
mechanical fasteners. An inquiry to 3M's technical support for an
alternative product recommendation was unsuccessful.
One dealer uses Dow Corning 795 silicone with fasteners every 8 to 12 inches around the periphery. He cautioned that large clearance holes need to be drilled in the acrylic to avoid cracking from the thermal expansion stresses. I was reluctant to deviate far from the builder's original intentions. Perforating the cabin trunk with holes for fasteners seemed like an invitation for leaks and long-term maintenance requirements. Moreover, we did not think the "industrial" look of closely spaced fasteners would enhance the lines of our boat.
South Shore Yachts offers a large selection of replacement parts, including windows, for old C&Cs. They recommend a methacrylate structural adhesive manufactured by ITW Plexus. Plexus MA320 is a two-part adhesive with a modest open time and relatively short cure time. More importantly, the cured resin will stretch 100to 140-percent before it breaks. And it has
exceptional adhesion to acrylic, fiberglass-reinforced polyester, epoxy, and gelcoat. It serves as both a structural adhesive and a sealant. I discussed the application with the regional manager for ITW Plexus, and he agreed this was the proper choice.
The final decision was choosing glazing material. The original windows were tinted 3/8-inch thick acrylic, commonly called by its trade name, Plexiglas. I considered using polycarbonate, trade name Lexan, which has superior strength. If the windows were large, I might have felt more comfortable with polycarbonate, but the Landfall 35 windows have less than 10 inches of unsupported span. Acrylic is much more scratch-resistant and somewhat easier to fabricate. I requested quotes from plastics distributors and South Shore Yachts on cut-to-pattern, cut pieces, and full sheets. I decided to purchase a full sheet from a local distributor and fabricate the panels myself.
Made a tracing
South Shore Yachts will fabricate finished
replacement windows from patterns. For a while I was contemplating
this alternative and made a tracing of the window on drafting vellum.
I nsed this pattern to fabricate one panel in my shop by carefully following
the outline with a band saw and finishing with a horizontal belt sander. It
did not fit exactly; I had to sand and trim the panel before it would fit the
opening. I recommend using the original windows as
I rough-cut four pieces from the 4 x 8 sheet using a 4 1/2-inch PorterCable trim saw. A saber saw could also be used, but it would be slow and tedious work. I purchased a special acrylic plastic blade for the trim saw which, according to the marking on the blade, is supposed to run with the teeth backward. I challenged the factory on this and was assured this is the correct rotation. The blade performed equally poorly running in either direction. The teeth appear to have insufficient set, thus the kerf is too narrow and the blade overheats. I switched to a fine-tooth carbide wood blade and cut the remainder easily. One caution: narrow strips tend to chip and shatter. Try to leave at least 1/4 inch for trimmings; it will have less tendency to shatter.
Two router bits
I also purchased two carbide router bits with ball-bearing followers on the end. One is a straight bit, sometimes called a laminate trimmer, and the other a 45-degree chamfer bit. You might save a few dollars using high-speed steel router bits,
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