Stretched Acrylics
Stretched acrylics are increasingly being used in boat windshields and it's about time. This version of acrylic starts off as a cast acrylic block that is heated and machine-stretched biaxially. The result is an enormously tough and rigid sheet that is used in some high performance fighter jets, such as the F-18. Also all exterior windows on passenger jets are stretched acrylic.
The pluses for stretched acrylic (MIL-PRF-25690) are rigidity under impact, toughness and perfect optical qualities. The cons are the elevated cost not only of the sheet but also the tooling.
Stretched acrylic is very hard to form because at above certain temperatures it goes back to being a block. Acrylico has a great deal of experience with stretched acrylics at our sister company, Control Logistics, where we manufacture almost exclusively from this material.
Polycarbonates
When it comes to competition and performance boats, polycarbonate windshields are necessary due to their superior impact resistance.
Polycarbonate windshields do have their shortcomings, however. Their enormous flexibility means that apertures have to kept to a minimum and a great deal of thought must be given to their attatchments. The other problem with polycarbonate is that it's extruded and the extrusion lines make optical quality a challenge.
Polycarbonate windshields and canopies also scratch very easily and are vulnerable to UV, so they have to be hard-coated after being formed.
Hard coating has come a long way. The best place to see hard coatings is on the headlights of modern cars. In the late 80's they began to make headlights out of polycarbonates and a couple of years later they turned yellow. In the mid 90's they began hardcoating and now you see crystal clear headlights...