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New Lights For Old Ports and Windows by Bob Biles [excerpt from Good Old Boat magazine]

Seaworthy Goods' Good Old Boat article about plastic for boat ports and windows

For decades, most recreational boats have been built with
hatches, windscreens, and ports made of rigid transparent
plastics. Clear plastics have replaced glass because of their
toughness, cost, ease of fabrication, and durability. Despite
these great qualities, there comes a time when any good old
boat needs to have some not-so-good old plastic replaced.

The two transparent plastics most commonly used on boats
are acrylics and polycarbonates. Acrylics, known
commercially by familiar names like Plexiglas and Lucite, have
a longer history in the marine industry than polycarbonates,
which are sold under trade names such as Lexan and
Makrolon.

Both types of plastic come in a wide variety of formulations
and tints. Each is available in a range of thicknesses with
those in typical use on boats being from 0.06 inch to 1 inch.

Physical Properties
Clarity -- Both acrylic and polycarbonate are available in clear and a range of transparent tints. Either plastic has
visible-light transmission values that approach or exceed 90 percent, which is comparable to glass. Clarity is most often
affected over time in both plastics by surface abrasion (scratching or scuffing) or prolonged exposure to ultraviolet
radiation in sunlight.

For many years, acrylic was the preferred material in marine applications because polycarbonate, in its natural form, is
much less resistant to UV. Old acrylic too long exposed to the sun usually develops crazing that goes right through the
plastic, but this could take decades to happen. Overexposed polycarbonate takes on a yellowish cast and the surface
becomes hazy. In subtropical climes, this could happen in a year or two. Chemists went to work and developed additives
and surface coatings for special grades of polycarbonate that increased UV resistance so it's now comparable to that of
acrylic. ...

Acrylics and polycarbonates are very different plastics.
Whether you're replacing old parts or planning a new project
to make your boat even better, understanding their relative
strengths and faults will help you determine the better
choice for the job.

For Bob's entire article, get a print copy of the March/April 2010 issue of Good Old Boat. For his online info about
polishing marine acrylic and polycarbonate, go to the GOB reader services section.