What's the thickest polycarbonate in your opinion would be allowable or practical for a cal cruising 46. This added weight no doubt changes the righting arm and center of gravity of the boat
I can't answer that question about the center of gravity. I think a supported one piece panel spaning across all the windows on each side (on the outside), should be stronger than the individual windows themselves. You're concern is that a wave hitting from the side will blow a window inward, since these windows are not really supported that good against sideways forces. One large panel across all the windows will be much stronger, and almost any panel thickness will be better than no panel...but I would say at least as thick as the window is now.