Reprinted by permission of

by Dean Hedstrom

After 20 years, the flush windows in our C&C Landfall 35 had been ravaged by exposure.They were suffering from age. One window had a minor leak that I had been battling for years. Two others had developed transverse cracks. All were deteriorating optically from UV exposure and a patina of scratches.
I consulted several sources and received many differing opinions on materials and methods for installing replacement windows. After sorting through the opinions, all it needed was a few hours in the shop and a weather-friendly day in the marina. I now have clear new windows and some new skills I hope not to use again for a long while. Anyone with modest woodworking tools, some energy, and an assistant can accomplish the same.
The original factory installation fixed the acrylic panels to a rabbeted recess around the window opening with a methacrylate structural adhe­sive. This is a bonding medium only; the windows were sealed with a silicone caulk. The
  methacrylate resin is applied to the opening flange and an accelerant applied to the acrylic panel. The panel is held in place manually for the few seconds the adhesive needs to activate. Think Superglue in paste form.
The methacrylate structural adhesive used in the original window installation, while extremely aggres­sive in bonding acrylic to gelcoat, was very rigid. The difference in thermal coefficient of expansion between acrylic (large) and cored fiberglass (small) created a lot of stress on the bond. The minin1al compliance or flexibility of the adhesive may have contributed to the failures.

Maintenance problem
The silicone caulking used in the original factory installation created a maintenance problem as well. It was difficult to reach the surfaces between the acrylic panel and recessed flange. Thus, after removal of the old caulk, cleaning was nearly get impossible. Sometimes we would lucky and succeed in removing a long strand of silicone caulk. This was a mixed blessing
  because it meant the silicone had not bonded the first time. Most often we could only scrape out small pieces at a time. As you would expect, mold and slime tended to grow in the damp places. It was not possible to adequately clean the surfaces in the gap to assure good adhesion for the caulking. I tried using other materials, but the leaks inevitably returned.

I always washed the windows with clear soapy water and polished them with Meguiar's Mirror Glaze No. 17 plastic cleaner followed by Mirror Glaze No. 10 polish. The elements, helpful guests, and other hazards took a toll on the surface finish of the win­dows that Mirror Glaze was unable to combat. Our outlook from belowdecks took on a permanent haze. The crack­ing may also have been a sign of age embrittlement. Since losing a window completely would endanger the vessel and her crew, it was time to tackle window replacement.

I spoke with several boat yards,

Author Dean Hedstom's C&C Landfall 35 with aging ports.
First remove the old ones and then secure new ones while the sealant cures.