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hellosailor · 21-12-2007, 15:50

""scratches in Lexan(polyC) can presipitate failure". "
GE, DuPont, Rohm & Haus, everyone who make acrylic and polycarbonates as either resins or "structured" (i.e. pre-cast sheet) forms, will tell you the same thing. Crazing is a structural failure starting in the material, whether it is acrylic or polyc. Crazing can come from improper installation (which causes stress crazing) or from excessive UV exposure (and there are hundreds of varying grades of material, with and without UV resistance ratings or UV protective layers) or from exposure to common chemicals.

Used any wax on the boat? Odds are it has a naphtha solvent base. Get it on the plexi, or polyc, and congratulations you have started failure modes. Neither of those plastic families should be exposed to petrochemicals of any kind.

It is all well documented, and the different source makers all pretty much agree in their recommendations and precautions. Polycarbonate ranges from roughly 10x to 100x stronger than acrylic, in the same thickness. If you want a deck hatch or portlight that can withstand the extreme impact of green water breaking off a 50' wave, or your boat pitchpoling, you will want polycarbonate and you will gladly pay 4x more than acrylic costs. And then pay 4x more again, to get the highest UV-resistance and scratch resistance in the material. You'll find the same thing in acrylic--that you pay more for UV and scratch resistance. You'll just wind up with a sheet 10x thicker to begin with, and still only a fraction of the strength.

21-12-2007, 15:50	#39
hellosailor Registered User Join Date: Apr 2006 Posts: 3,997	""scratches in Lexan(polyC) can presipitate failure". " GE, DuPont, Rohm & Haus, everyone who make acrylic and polycarbonates as either resins or "structured" (i.e. pre-cast sheet) forms, will tell you the same thing. Crazing is a structural failure starting in the material, whether it is acrylic or polyc. Crazing can come from improper installation (which causes stress crazing) or from excessive UV exposure (and there are hundreds of varying grades of material, with and without UV resistance ratings or UV protective layers) or from exposure to common chemicals. Used any wax on the boat? Odds are it has a naphtha solvent base. Get it on the plexi, or polyc, and congratulations you have started failure modes. Neither of those plastic families should be exposed to petrochemicals of any kind. It is all well documented, and the different source makers all pretty much agree in their recommendations and precautions. Polycarbonate ranges from roughly 10x to 100x stronger than acrylic, in the same thickness. If you want a deck hatch or portlight that can withstand the extreme impact of green water breaking off a 50' wave, or your boat pitchpoling, you will want polycarbonate and you will gladly pay 4x more than acrylic costs. And then pay 4x more again, to get the highest UV-resistance and scratch resistance in the material. You'll find the same thing in acrylic--that you pay more for UV and scratch resistance. You'll just wind up with a sheet 10x thicker to begin with, and still only a fraction of the strength.