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Old 19-10-2021, 12:15   #1
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Fixed portlight replacement

Im planning on replacing the fixed portlights on my 30 1992 Sabre MKIII. They are some sort of plastic. Other than cost, what would be the downside to replacing them with tempered glass?
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Old 19-10-2021, 17:27   #2
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Re: Fixed portlight replacement

Tempered glass is not "bulletproof" or anything like that. It's great stuff, until it isn't. Favorite tempered glass story: Many moons ago I worked in what was then the second largest tropical fish store in the US. We'd just received the latest and greatest fish tanks, made out of tempered glass. One of the owners set up a 55 gallon tank in the front of the store. Any time a good customer would come in, he'd take them over to the tank, pick up a hammer, and wack the front of the tank. It really was impressive. Every Tuesday night, after we got in a fish shipment, our very best customer would come in. He was... Well, everyone in the world would recognize his name. Lenny couldn't wait to show him. The 2 of them stood in front of the tank, Lenny wacked the tank with the hammer. Yup. Tempered glass only holds up to abuse for so long. 55 gallons of water poured out of the tank, soaking them both from the waist down. Well, Lenny from the waist down. The dude was huge. Thighs down.

So, no. I really wouldn't recommend it. Cast acrylic (NOT poly carbonate). If it's mechanically fastened, use butyl tape. If it's "glued" in place, use Dow 795 (make sure it's in-date).

Good info here: www.hatchmasters.com
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Old 22-10-2021, 06:18   #3
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Re: Fixed portlight replacement

By way of amplification of Bill Streep's excellent advice: Acrylic is plexiglass, poloycarbonate is Lexan. Acrylic is much harder, but relative to polycarbonate not as strong. Acrylic will splinter where polycarbonate will bend. Polycarbonate will scratch where acrylic will not. The usual answer is thicker acrylic. Evenually it will craze, like the acrylic lens on your car's headlights, so butyl tape is a good idea.

I actually use polycarbonate on ports where I don't need clear vision and do need strength, but in the general case, no, go with acrylic.
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Old 22-10-2021, 09:11   #4
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Re: Fixed portlight replacement

Great advice above, too. The biggest problems with polycarbonate (Lexan) are: 1) soft, 2) very flexible, sometimes too flexible - it doesn't make a good hatch cover because it will flex enough that someone could step thru it 3) it doesn't like UV. After a year or so in the sun, it's strength will be down to that of cast acrylic. They do make some UV stable polycarbonates.
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Old 22-10-2021, 10:56   #5
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Re: Fixed portlight replacement

Quote:
Originally Posted by bstreep View Post
Great advice above, too. The biggest problems with polycarbonate (Lexan) are: 1) soft, 2) very flexible, sometimes too flexible - it doesn't make a good hatch cover because it will flex enough that someone could step thru it 3) it doesn't like UV. After a year or so in the sun, it's strength will be down to that of cast acrylic. They do make some UV stable polycarbonates.

Can you put any sort of UV reflective film over either Lexan or Acrylic to protect against the crazing and breakdown?
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