Replace Hatch Glass

11/02/2017

Dropped a snap shackle onto the foredeck hatch and put a nice hole into the Plexiglass! Rather than buying a new $2500 hatch, here’s how to just replace the glass.

Take measurements for the replacement piece, or just keep the old piece to copy.
Batten the hatch so the rain won’t get in. I put some waterproofed Sunbrella I had laying around and tied a rope around the hatch to secure it.
Pry off the old glass.
1. Use a knife to cut the old glue
2. Slide a putty knife into the edge and work it’s way around, loosening more of the old glue
3. When the gap is large enough, fit a large screw driver to help pry the old glass up while continuing to work the putty knife around
4. Eventually, the while thing should start to unstick and hopefully come out in one piece.
5. I got a little greedy and pulled up on the glass before working the putty knife all the way around and broke the old glass in half. Bygones.
6. Keep the old piece to match the new piece exactly. The new glass must be within a few millimeters to fit perfectly.
Find a replacement window.
1. You have a selection of materials.
  1. Cast Acrylic is strong, stays clear the longest, and requires the least maintenance. Good UV resistance. However it can crack (as mine did when hit with the heavy snap shackle).
  2. Do not use Extruded Acrylic. It will not last.
  3. Lexan is also a well-known product which is stronger and “bouncier” than Acrylic. The dropped snap shackle would probably have bounced right off. However it scratches and fades quicker than Acrylic. It’s also about 35% more expensive than Acrylic.
  4. Do not use glass. It is 17 times weaker than Acrylic and is brittle and sharp when broken.
2. I replaced mine with the original material, 13/16″ Grey Tinted Cast Acrylic, custom cut by Min Plastics on Oahu, Hawaii for $63.
3. 13/16″ is fairly thin, but my hatch frame has 3 support beams to provide extra strength so you can stand on it.
Clean the hatch frame.
1. Try scraping with a paint scraper, dremel with brush attachement, metal brush (don’t use a steel brush on aluminum or the bristles could introduce some galvanic corrosion over time), rags and Acetone or whatever else you can think of to make the hatch clean.
Glue in the new glass
1. Again, you have a few products to choose from to adhere the glass to the frame
  1. Sikaflex 290UV.
  2. Dow Corning 795 Silicone Building Sealant.
  3. 3M VHB 4991 1/2″ wide double sided tape.
  4. Do not use 3M 5200. It will harden and may crack the glass. Also, Acrylic attacks the 5200 glue, weakening it over time.
  5. Do not use 3M 4000UV. I tried it and it lasted a week.
2. Follow the instructions of your product EXACTLY! No shortcuts. The goal is perfect adhesion and no leaks.
Clean up and you’re done. Here’s to 30 more years of leak free star-gazing from your V-berth!