So why don’t boat manfacturers use automo type glass instead of lexan that crazes like crazy? Engineering the window area / hatch covers so that it doesn’t flex much? Just asking...
Windows - really?
- Thread starter PGUTIERREZ
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That, and the fact that most port and hatch windows have a slight curvature which would be hell to bend glass upon.
It's a question of money. Most of the windows on super yachts are glass. I have glass windows on my Shannon motorsailer. After 8 years they are clear as when new - as you'd expect from glass.
If you do plastic - Lexan crazes and scratches much worse than cast acrylic (e.g. plexiglass). I think all standard boat hatches are cast acrylic.
Steve Dashew uses 3/4" thick toughened safety glass in his ocean going powerboats. I'm not sure you could break 3/4" toughened glass with a hammer SetSail FPB » Blog Archive » Glazing
One of the big producers of marine glass is Gariboldi Glass in Vancouver. Besides yachts they do pilot boats and many CG patrol boats. Glass Supplier, Glass Contractor, Ceramic Frit
If you do plastic - Lexan crazes and scratches much worse than cast acrylic (e.g. plexiglass). I think all standard boat hatches are cast acrylic.
Steve Dashew uses 3/4" thick toughened safety glass in his ocean going powerboats. I'm not sure you could break 3/4" toughened glass with a hammer SetSail FPB » Blog Archive » Glazing
One of the big producers of marine glass is Gariboldi Glass in Vancouver. Besides yachts they do pilot boats and many CG patrol boats. Glass Supplier, Glass Contractor, Ceramic Frit
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The lens on ports and hatches needs to be able to take a "green water' wave as well as an errant human-propelled boot.
While Acrylic will do a pretty good job and, depending on initial product quality, will also resist UV for many years, for real impact protection designers prefer polycarbonate ("Lexan").
Safety glass is also great, until you whack it with a block or a handle and crack the surface, but can only be formed for the normal curvature of boat cabins with *very* expensive molds. I saw the set of new fixed ports for a 50 foot motor yacht recently that were custom formed, and each shape (appox. 4' X 2.5' in general size but curvy) was $2500. delivered. (!)
There is a slight curve for the four fixed polycarbonate fixed ports for our particular boat. I previously replaced them in 1995, and the lens surface (even with extra layers of UV resistant surface material) was badly hazed after 25 years. New ones going on soon.
Note that our boat was designed for extended offshore sailing, and that's a reason that this material was specified. Ours are fastened with screws and also adhesive.
Things like this are specified by the design brief, and you have to choose your level of design and level ($$) of build quality according to your needs.
As nice as glass can be, it is just not always the best material for the task...
While Acrylic will do a pretty good job and, depending on initial product quality, will also resist UV for many years, for real impact protection designers prefer polycarbonate ("Lexan").
Safety glass is also great, until you whack it with a block or a handle and crack the surface, but can only be formed for the normal curvature of boat cabins with *very* expensive molds. I saw the set of new fixed ports for a 50 foot motor yacht recently that were custom formed, and each shape (appox. 4' X 2.5' in general size but curvy) was $2500. delivered. (!)
There is a slight curve for the four fixed polycarbonate fixed ports for our particular boat. I previously replaced them in 1995, and the lens surface (even with extra layers of UV resistant surface material) was badly hazed after 25 years. New ones going on soon.
Note that our boat was designed for extended offshore sailing, and that's a reason that this material was specified. Ours are fastened with screws and also adhesive.
Things like this are specified by the design brief, and you have to choose your level of design and level ($$) of build quality according to your needs.
As nice as glass can be, it is just not always the best material for the task...
i just did cast acrylic flush mounts in my boat a few weeks back. a few days ago we had a very windy night. I now have and arc of scratches in my shiny new windows from my tarp.....
My Sabre 30 had safety glass in the fixed ports.
Acrylic wins in the port lens debate. See this article from Select Plastics/Hatchmasters.
hatchmasters.com
Acrylic wins in the port lens debate. See this article from Select Plastics/Hatchmasters.
Acrylic vs. Polycarbonate - HatchMasters
I spend inordinate amounts of time discussing the pros and cons of acrylic and polycarbonate. In so much as I would like to bring some clarity to this issue. Please consider the following: All major hatch, portlight, and window manufacturers use Acrylic in offshore / bluewater marine products...
hatchmasters.com
Install cover on them and eliminate crazing. Most boats spend 90% of their life in a slip. Covers on them during this time will eliminate the problem while taking them off for the other 10% will have no ill effect ( although I just leave mine on).
Auto glass is weak in comparison to polycarbonate. My local glass guy gave me a demonstration. I had removed the original 1961 tempered glass during some work on my boat. The glass had light scratching around the edges from years of varnish maintenance.
He told me they sold a lot of safety or laminated glass for fishing boat windows, a few sailboats as well. Pretty easily broken but at least the remains stay in one piece.
He took a few samples of auto glass and broke it easily with a hammer. He explained in fact it's weaker than solid glass as it's actually 2 thinner plates. But it laughs at UV and works great in the right applications.
Then he took some tempered glass and tried to break it with a hammer. It took a large wallop on a skinny scrap piece to finally break it. Then he explained the process to replace the tempered glass. They would have to cut my shaped glass and then send it out to fire, or temper it. It would have been pricey.
I decided the scratching around the edges didn't bother me.
Incidentally, he pointed out on my 1961 glass, the 4 indentations around the perimeter where pins held the glass up during the firing. I also buy all my acrylic and polycarbonate material from him. I used 1/2" Lexan on my wooden overhead hatches, that would stop a bullet, but it does craze over time. You can't have it all,...
Many years ago there was a company, Cyro-plastic, in Sanford, Maine that made plastic parts. They made those curved windshield for motorcycles, bubble skylights, etc. I seem to remember heating the plastic to 400 degrees and it would bend to any shape or surface. I always wanted to try it at home, but my wife would threaten me within an inch of my life if I touched our oven. Did a test to dry wood once with the microwave when she wasn’t home. Interesting effect. Had two extinguishers ready and it was a good thing.
This is the long term solution. Replace the crazed acrylic, then make or buy covers. Better for the interior too as it keeps the sun off the fabric and woodwork and makes the boat cooler in the summer.Tempered glass is touchy stuff. When it breaks, it does not break into shards like regular glass, rather in to smaller mostly round pieces. I had a TV stand once with a tempered glass top shelf. In the middle of the night we awoke to find the TV on the floor along with thousands of pieces of glass. The tempered glass shelf had self destructed for no apparent reason.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,746
Interesting thread. I have laminated glass ports that I need to reset, along with some replacement glass this year. I am hoping I'll be able to get the non cracked glass free from the frames so I can reinstall with new seals.
I have been concerned about the Green water - open ocean issue since getting the boat. I have resolved that in such conditions only answer is to have some shutters made to cover the glass. Then bolt the shutters in place. Since coastal sailing is the plan, I tend to find a port to park in and avoid a long passage when Green Water will be sweeping the decks.
I have been concerned about the Green water - open ocean issue since getting the boat. I have resolved that in such conditions only answer is to have some shutters made to cover the glass. Then bolt the shutters in place. Since coastal sailing is the plan, I tend to find a port to park in and avoid a long passage when Green Water will be sweeping the decks.
Sailed on 55ft custom pilot house with rather large pilot house windows. 3/4” tempered glass. Acrylic was too flexible and lexan too dark at night. We tested them out in a 3 day gale with winds over 50knots gusting higher. Plenty over blue water coming over the pilot house as we buried the bow in the 20-25’ breaking seas. Glass held up fine. Smaller ports acrylic would have worked.
Auto glass in an offshore boat would not be insurable. The toughened safety glass that meets Lloyds and ABS standards is hard to break with a 10lb sledge. A bigger risk with all glazing (including glass, Lexan and Plexiglass) is if it flexes enough to pop out of the frames during a wave strike. That's why better installations are now bonded rather than framed.
I suspect that's why our polycarbonate fixed ports were secured with screws as well as adhesive. Flexing that much might quite rare, but still possible if smacked by enough water. I have been offshore in 19 foot seas that put green tops over the deck sometimes, and would never choose to be in anything stronger. Hopefully conservative weather routing will let me avoid that... or just walking inland and sitting under a tree... !
(Per an old story, you walk inland with two oars and when someone asks you what they are for, you have walked far enough!)
My 1969 Columbia has large framed acrylic windows, about 5 feet by 1 foot that if done in safety glass would cost more than the rest of the boat. They've been replaced probably three times in her 52 years. There are also several small framed ports about 6"x14" that are laminated glass. They are original but have gotten so milky over time that they're hard to see through. They were like that when I got the boat 15 years ago so about 40 years old at that time. So neither material is perfect.
I like the sun cover idea. Some of my cabin cushions have faded areas from the sun shining through the big windows, covers would prevent that too. Lexan would also help as it filters UV which is why they make eyeglass lenses out of it.
I like the sun cover idea. Some of my cabin cushions have faded areas from the sun shining through the big windows, covers would prevent that too. Lexan would also help as it filters UV which is why they make eyeglass lenses out of it.
Fast Olson. We didn’t choose to be in those conditions. Bringing a 55 foot aluminum purpose built boat from St Thomas to the Chesapeake. Once you are 3 days out of St Thomas you are committed. 3 cold fronts coming off the plains formed up to make for a rare tropical depression. Lesson learned. Don’t try to make that trip in April. Nothing like being 300 miles off St. Augustine in 25 foot breaking seas. No outs at that point. Never again. Many waves broke over the pilot house. The main cabin had Lexan small ports. The pilot hose had large windows of tempered glass. We stayed in the pilot house while on watch. One person in a gimballed chair at the nav station and one in the pilot berth across from it.