Porthole Glass

[Dan Cavins]

Hey folks. Wondering what you have used for porthole glass? I know Lexan is good but how about that plastic stuff you can get in the hardware stores? These will be small, about five inchs wide, cateye-style. They are fixed (closed)and will be on a sharpie that will spend most of it's days on the trailer. If the plastic stuff works, great. If not we'll move up. Thanks, Dan.

[Mike Keers]

Dan,
The stuff at the hardware stores is most likely Plexiglass, under that or another name. It's fine for ports, but not as scratch resistant as the much more expensive Lexan, so go easy on the cleaning.

I've always gone for ther heavier stuff myself, but some 'authorities' in the boatbuilding books say 1/8" is plenty thick enough for a small port like you're planning. This stuff is sold most everywhere as replacement panels for screen/storm doors.

Personally, I'd go for 1/4" in a smaller port like yours (but it might be overkill), and 3/8" to 1/2" when they start getting really large. But then I observe the "too strong never broke" theory. Still, if 1/8" is OK for something as large as a two foot square door.....should be fine for your little deadlights.

There are a few ways to mount the stuff, detailed in many books, but clear silicone is a great bedding no matter what. If you go with screws or bolts, drill the holes oversize, and use pan head screws or flat washers against the glass, not flat head (countersunk)--the stuff expands and contracts with temperature, and if you fix it too rigidly it's likely to crack from the holes out to the edges. Of course 1/8" is a bit thin for countersinking anyway, if you had a mind to in the first place.

I've made many ports like this, the largest over five feet long and 16" tall, and never had a leak or one crack, by bedding well in silicone and using the oversize hole, flat washers, and not overtightening the bolts--I use Nylocks and just snug them up.

But different oars for different long boats--I'm sure you'll hear alternate suggestions once we get the ball rolling.

Got any pics of the boat? Tell us more about it!

[Dan Cavins]

Thanks Mike. Your plan sounds pretty much like what I was thinking. No sense in complicating those little things which will go on a nice but simple boat. Mike it's an NIS-23 and the story is at http://www.norwalkislandssharpie.org if you care to look. It's almost current. Don't think I've killed the boat yet. Thanks, Dan.

[Steve Lansdowne]

Down here the BIG ORANGE store carries small pieces of Lexan along side their plexiglass. It is more expensive, but for the small amount you'd need that might not amount to much.

[imported_Conrad]

I'd take the time to find some lexan or other proprietary hardened brand- the regular stuff will scratch just with washing it with a car brush, heck, even the lexan is really pretty soft compared to glass. I think a bit of extra effort will pay off- the expense isn't even worth talking about for the amount you'll need.

[John Blazy]

MR-10 Lexan is what you want. GE is a leader in hardcoat technology, and the scratch-resistant (AR designation for abrasion resistant) coating on the MR-10 product is revolutionary. I cut it bare surfaced on my tablesaw, and still see no scratches. I use it all the time in the laminates I make and market, as well as "glass" viewing bottoms for my boats. Lexan is a trade name for Polycarbonate (which is far tougher than Plex, i.e. acrylic sheet), and other AR polycarbonate brands include Hyzod AR, and Cyro's Cyrolon AR. Many plastics distributors will sell cuttoffs or scrap by the pound and that is where I'd start cuz its expensive (5 bucks psf). Look up GE polymershapes on the web for distributors, or look up Curbell plastics. - JB

[Nicholas Carey]

Why not go to a glass store and order tempered safety glass cut to the proper shape? It will last longer and not scratch or yellow from UV damage.

[Ron Williamson]

If you to use real glass in a boat bottom it should be laminated, not tempered.
Tempered glass,while very strong,will shatter into tiny little bits if struck by something pointy.
Laminated glass has a layer of clear plastic laminated(hence the name)between two sheets of regular glass.It will crack and spiderweb but still be water-tight.
Around here they all(including DECENT plastic) cost about the same per sq.ft. except that tempered glass has a 4sq.ft. minimum.At $8/sq.ft.,that hurts.
R

[Mandoliniment]

In my experience, the Lexan is much less scratch resistant than Plexiglass, but is, for all intents and purposes, shatterproof. At the children's museum where I work we generally use plex expect for flat surfaces that might, say, have someone stand on them - there we use the much stronger lexan. Stronger, but much softer, and quickly looks "fogged", while the plex remains pristine.

We took an old sheet of Lexan and smashed it with a bowling ball many times; no breaking. Folded it in a vise; it was happy. Bent, but happy. crazy strong stuff.

My impression is that Lexan is used in boat windows because it won't break when hit with a big wave, glass or plex certainly would. I'd think with a small window this wouldn't be a big issue.

One final note - cutting and drilling plexiglass requires special tooling; ask your plastics dealer what you'd need. Lexan works fine with regular woodworking tools.