see the links for some good information... it can be an easy job if you read up and understand the need for good preparation.
I have actually watched the tape method used for the initial install/placement of the windows (5/8" polycarbonate AR), then bolts added with sealer installed around the windows.... it makes it seaworthy and looks great...
no matter what material you use, i would highly recommend you get it with the AR (abrasion resistant) coating.... different manufacturers may call it by another abbreviation, such as the Makrolon brand calls it MR10 = Mar Resistant
I'm guessing the windows, themselves, arent the issue. Albeit they are dark tinted, which I can see replacing with clear.
1) If doing it myself, does plexiglass fill the bill? ANd should I also opt for a thicker panel?
2) I always believed the darker panel provided more privacy, but I'm also attuned to having more light comer in. Sailing Lake superior for just so few months a year, I'm not sure darker is needed. Drapes help.
3) and is it as easy as tracing an outline around the existing panel and cutting New?
4) Because this is an acrylic panel, with a strip frame...it was mentioned that "Dow Corning 795 Silicone Building Sealant", would do the trick. Anyone else?
i would NOT do tinted windows, but the UV coating to help reflect some of the sun helps a lot... as you have said, when you need privacy, pull the curtains. no matter how much privacy someone thinks the dark windows give, curtains give more. the tinted glass doesnt give any privacy when you want it most, such as at night when you are tied to the dock with a light on inside...
and on the gloomy days, is nice to have as much light coming into the boat as you can get....
yes, the dow 795 is good stuff...
plexiglass (acrylic) is good. it is naturally more scratch resistant than lexan (polycarbonate).... but still get it with the scuff resistant finish on it, because you want it to last many years without having scratches in it.
I would go with no less than 1/4"... 3/8" is better but you may be limited on how thick of glass the frames will hold.... thicker is stronger but more expensive.
and you can find either acrylic or poly carbonate with different brand/trade names at a much cheaper cost, that the ones listed above.