Hey Dave,
Not only would Gramps be proud, he would also be very impressed, as I am!
It's nice to know, that I, thanks to my Gramps, have finally contributed some useable info to this site, instead of taking it all the time.
It didn't occur to me to make them out of fiberglass but I'm sure they're just as strong, and will probably outlast ours...we have 30 years so far:P Seriously though, great thinking and excellent work! It's tough to tell in the pics but is the forward edge of the lower panel, curved upward like ours? I think that's important to ensure no water forcing downward on the plate.
Also, it's great to hear your comparison, with and without. I have never operated ours without, but I can see by your experience, my minimum planing speed would be much higher, and sensitivity lower as I had anticipated. I'm glad Gramps was on top of that!
12 mph is pretty darn good!
Nice work!
Brandon