Join Date: Apr 2006
Thanked 248 Times in 243 Posts
Rep Power: 15
Re: Where to get new portholes....material?
Once a piece of glass has been tempered (usually by heating it in a particular way and time) it surface hardens, and the "skin" of the glass literally contracts to squeeze the entire piece of material. The same thing is done to automotive brake rotors. If that tempered surface is penetrated in any way, by drilling, slotting, cutting an edge off, etc. you wind up with the equivalent of taking the cap off a toothpaste tube: Something is going to come out. (Shatter from the uneven squeezing, actually.)
There ARE places that have their own annealing ovens, and they can cut and machine glass to your specific needs and THEN anneal it afterwards. Those places are hard to find and usually not cheap. I wanted to replace the glass in a scuba mask because the RX lenses that were epoxied to it (optical epoxy is forever) and replacement lenses are no longer made. Well, there's one shop that specializes in this stuff, they said no problem, they'd cut matching new glass and temper it, they do it every day. Everyone else? Says it can't be done.
So it very much CAN be done. But acrylics (Plexiglass) or polycarbonate (Lexan) are generally going to be way simpler to work with and way stronger. Each of the major manufacturers makes one to three DOZEN different grades of each of these. The stuff in the plastics store is usually cheap, suited for napkin holders. The good stuff, which is designed for exterior structural glazing, has less thermal expansion (so less crazing down the line) and UV protection and scratch resistance. And all of that can easily double or quadruple the cost of material.
What Mark Plastics usually supplies are exact OEM replacements. Which are usually designed to keep out spray and rain. If you consider that on a really bad day, you may have a fully loaded spinnaker pole come stabbing into a portlight...then 1/4" or thicker polycarbonate becomes way more attractive than the typical 1/16" acrylic. You can beat on the polycarbonate with a sledge hammer, it is probably as strong as the hull. The acrylic? Swing a plain hammer from your elbow, it will shatter right through.
Proper cleaning (always with a rinse & moist cloth, never petrochemical or ammonia based cleaners) and using a good plastic polish every year or two, should keep plastic in top shape for a long time.