Jude,
The material names you refer to are either Polyacrylate or Polycarbonate. Of
the two, polycarbonate is the strongest. There are three grades of
polycarbonate, uncoated, coated on one side and coated on both sides. Of the
three grades the double coated variety is the most expensive and the only
choice I would make. It does not scratch easily and is much more resistant
to UV damage. Secondly, do not use silicone for a bedding material, it is
inferior in both adhesion and durability in the marine environment. You
should use a polysulfide rubber compound that is designed for this
application, like Sikaflex 292 (I think). You need to allow at least 6mm of
gap all around, as the expansion rates of the materials are different.
Steve

"Jude Douglas" wrote in message
...
I sure hope I don't get a war of words going, but I would like get some
recommendations on which sheet material to use for our sliding main
hatch: polyacrylate (Plexiglas, Lucite, Acrylite, Perspex, etc.) or
polycarbonate (Lexan). I know Lexan scratches easily but it is very
impact resistant (falling winch handles or a whipping snap shackle). I
know Plexiglas is a bit cheaper than Lexan but it is not a concern for
such a small size of project. To reduce temperature expansion stresses
and drilling difficulties, I plan to just use a flat sheet with a
squishy bedding (silicone?) and a sort-of loose oak frame with a
retaining bracket.
Can anyone offer some suggestions as to which is a better choice
material?

Jude and Randall