I replaced all the fixed windows last year. Before doing so, I checked with several "experts" and nearly all said, in places where a wave could hit the window, I should use Lexan made by GE. As I recall, it cost about $150 for a 2''x4'' sheet 1/4" thick. I was able to cut all four windows from one sheet, with a bit left over.
~ Happy sails to you ~ _/) ~