[Public-List] Polycarbonate vs Acrylic (was: Anodizng aluminum parts)

[George Dinwiddie]

Lee Hines wrote:
>    In the Hydrographic Survey business we once used plexiglas for
>    underwater "windows" so as to allow the acoustic signals to pass
>    through but to prevent water from shooting up into the transducer well
>    while underway. We left specially placed holes in the glass to allow
>    water to enter but prevented bubbles from entering. The problem with
>    the plexiglas was that it shattered easily from either over tightening
>    retaining screws, impact or just vibration over time. We changed to
>    lexan and the problems went away. If we encountered a direct hit on
>    the lexan heaving up and settling down on the bottom then it would
>    fail but only in this extreme case. When thinking about using it for
>    windows I would think that it would be superior to plexiglas for its
>    ability to withstand impact and flexing that would make the plexiglas
>    shatter. A definite advantage should you be in rough water wanting all
>    things to remain the same as they were when you left. I do not know of
>    any negative when comparing the lexan to plexiglas maybe others do.

There's no question that polycarbonate (Lexan) is more impact resistant 
than acrylic (Plexiglas).  Given that the boats were originally 
outfitted with 3/16" acrylic portlights, going to 1/4" modern acrylic is 
probably plenty strong for coastal cruising.  If you're going to the 
southern ocean, you might consider a polycarbonate shutter over the 
portlights, as the frame itself might become the weak point.

Polycarbonate scratches more easily than acrylic.  It also yellows in 
UV, which acrylic does not.

My point is that either will do fine.  Many people make the assumption 
that polycarbonate /must/ be better because it's considerably more 
expensive.  My opinion is that for this application, polycarbonate's 
advantages are not needed and its disadvantages are a consideration.

BTW, I've seen that polycarbonate can crack from poorly drilled holes or 
rough cuts, also.  Take care with either type of plastic sheet.

  - George

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   When I remember bygone days                         George Dinwiddie
   I think how evening follows morn;            gdinwiddie at alberg30.org
   So many I loved were not yet dead,           http://www.Alberg30.org
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