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Old 28-05-2015, 18:32   #1
Jud
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Portlight replacement - tempered glass or acrylic

Hi all,

I'm in the process of replacing portlights on my custom-made steel boat. The original (20+ year old) portlights are 3/8" tempered glass. They've performed well, except that due to bad glazing, water got in around two windows over the decades, and when removing the windows, I noticed that rust had built up around the two windows and probably gradually "squeezed" the glass until it cracked - or, so I theorize, due to expansion/contraction in summer/winter of steel hull around windows and/or of glass. This happened to two windows (non-opening portlights) - they were not hit by anything, so I can't figure out how else they could have broken.

Anyway - so I'm considering replacing all the portlights with acrylic windows, which a plastic shop tells me isn't as impact resistant as Lexan, but is UV stabilized (Lexan isn't, they say). Glass, of course, is basically not affected by UV, and tempered glass is very strong --I plan on offshore sailing (but double the cost of going with acrylic).

Anyone have any advice re: glass vs. acrylic? Is glass overkill? I'm guessing acrylic would stand up better in terms of possible damage due to expansion (since it won't crack as easily as glass?). Thanks for any technical advice on pros/cons of each.

Jud
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Old 28-05-2015, 18:40   #2
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Re: Portlight replacement - tempered glass or acrylic

Really liked my old glass ports. Easy to clean, didn't craze or scratch, still going strong 40 years later. Personally would get safety glass rather than tempered if it will fit the frame. Tempered will shatter into a bunch of tiny pieces if hit just right. That would leave you with an open port. Not a good idea if you are in bad weather when it happens.

Currently have plastic port lights in my boat. Looked great new but already scratched and a little grubby looking after only a few years.
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Old 28-05-2015, 18:43   #3
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Re: Portlight replacement - tempered glass or acrylic

Many thanks - I know nothing about glass...so I assumed tempered was the way to go. Will look into safety glass too.
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Old 28-05-2015, 19:18   #4
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Re: Portlight replacement - tempered glass or acrylic

We went through the dilemma of tempered versus safety for our new build, went with tempered as apparently it is considerably more stronger than safety. I agree that the tempered shatters but it takes a far great force to do that. Our pilot house windows are about 2x3' and are 3/4" thick or 19 mm. Our hull ports are 1/2" or about 12mm. They are 6"x 18". After decades of dealing with frosty crazed plastic windows and ports, I really like real glass. It is quite possible there was some wracking of the frames to cause the glass to crack.
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Old 28-05-2015, 19:55   #5
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Re: Portlight replacement - tempered glass or acrylic

Plastic sucks, it will scratch quickly (like in the first second after you peel off the paper) but pexiglass (acrylic) is better than Lexan because it will scratch less. Safety glass can be cut by your local glass shop but tempered is custom made for your port, $$$.
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Old 28-05-2015, 20:44   #6
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Re: Portlight replacement - tempered glass or acrylic

I'd done our fixed ports in Lexan......never again. Nor would I do acrylic. I've even changed my sunglasses to glass.....there is no substitute!!!!


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Old 29-05-2015, 04:41   #7
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Re: Portlight replacement - tempered glass or acrylic

I have both. I went for safety glass for the side port lights and port holes, but have used 3/8 tempered for the sky light. I tried the acrylic route and it crazes and becomes opaque in time. I definitely prefer real glass over plastics. A good glass shop can cut most any shape. Never cheap though. 7 pieces of 12 X 12 X 3/8 tempered were $240 and trapezoidal shaped safety was $40 each.
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Old 29-05-2015, 05:01   #8
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Re: Portlight replacement - tempered glass or acrylic

Easiest way to break tempered glass is to hit the edge. If used, you need to insure that the glass is cushioned on all edges, that it won't shift and make contact with a point of impact. I believe safety glass may fog after not to long a time if any moisture gets to the edges.
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Old 29-05-2015, 09:35   #9
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Re: Portlight replacement - tempered glass or acrylic

Lexan - the industry joke is: "Lexan is NOT all it is cracked-up to be"

Acrylic - Inexpensive, easy to cut to size, relatively long lasting, does not shatter.

Glass - (tempered glass) depending on the shape, not easy to cut, easy to clean, relatively long lasting, safety glass will not shatter.
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Old 29-05-2015, 09:46   #10
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Re: Portlight replacement - tempered glass or acrylic

I've often wondered if glass shapes could be cut with a Waterjet. There seem to be a lot of those around, even some smaller shops. Just wonder if that would be cheaper than a glas shop. How does a glass shop cut a oval in glass?
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Old 29-05-2015, 10:05   #11
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Re: Portlight replacement - tempered glass or acrylic

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Originally Posted by keepondancin View Post
I believe safety glass may fog after not to long a time if any moisture gets to the edges.
Just about every windshield in every car is safety glass. They only use tempered in the side and rear windows. I don't think I have ever had a car with fog between the layers of the windshield.
To cut curves in safety glass, you cut a number of straight lines. You cut both sides, break it, squirt some lighter fluid in the break then set it on fire and it melts the glue between the layers. Then you can sand/grind the edges to your shape. I have never heard of a small glass shop cutting tempered glass. The water jet thing must be the ticket for those who have one.
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Old 29-05-2015, 10:08   #12
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Re: Portlight replacement - tempered glass or acrylic

With frames or recess I would go tempered. The long lasting clarity is well worth the cost and risk involved.

Unfortunately, our new boat has its deadlights bolted proud and tempered won't work. I'll have to go acrylic.

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Old 29-05-2015, 10:23   #13
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Re: Portlight replacement - tempered glass or acrylic

I don't think tempered glass will crack without completely shattering so I suspect the OP's original glass is laminated safety glass. I think this is the best choice since it will stay in one piece even if it breaks.

Has anyone tried glass in a Lewmar hatch frame?
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Old 29-05-2015, 10:33   #14
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Re: Portlight replacement - tempered glass or acrylic

Just discussed this glass vs plastic with local boatshop recently.
Over the years,they tried about every type of "window plastic"-Lexan,plexi,acrylic,etc.
Aside from expected scratchability,they found they all degraded by UV over time-discoloring,cloudiness,etc.
But the scariest finding was,when replacing windows they had installed 5-10 yrs previous,they had become "brittle" to the point that they would crumble or ,if dropped,or otherwise bumped sharply,would split or shatter.
The original plasticity had gone,& they had become hard & brittle.
This shop uses only glass now.They have a local auto glass shop cut & come install it on site,& are very pleased with results.Never thought to ask if they used "tempered",or auto windshield "safety" glass,but I could find out.
Personally,and aquaintances,have had various glass items-table tops,etc-made by auto glass shops at very reasonable cost- FYI

Grand Manan Boats (no affiliation) build mostly commercial fishing boats 30-60ft-which are used year round in N.Atlantic conditions (rough weather),though they have done some good yacht work also.

Just passing this along. / Len
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Old 29-05-2015, 11:14   #15
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Re: Portlight replacement - tempered glass or acrylic

Quote:
Originally Posted by Jud View Post
Hi all,

I'm in the process of replacing portlights on my custom-made steel boat. The original (20+ year old) portlights are 3/8" tempered glass. They've performed well, except that due to bad glazing, water got in around two windows over the decades, and when removing the windows, I noticed that rust had built up around the two windows and probably gradually "squeezed" the glass until it cracked - or, so I theorize, due to expansion/contraction in summer/winter of steel hull around windows and/or of glass. This happened to two windows (non-opening portlights) - they were not hit by anything, so I can't figure out how else they could have broken.

Anyway - so I'm considering replacing all the portlights with acrylic windows, which a plastic shop tells me isn't as impact resistant as Lexan, but is UV stabilized (Lexan isn't, they say). Glass, of course, is basically not affected by UV, and tempered glass is very strong --I plan on offshore sailing (but double the cost of going with acrylic).

Anyone have any advice re: glass vs. acrylic? Is glass overkill? I'm guessing acrylic would stand up better in terms of possible damage due to expansion (since it won't crack as easily as glass?). Thanks for any technical advice on pros/cons of each.

Jud
Acrylic like Lexon is bullet proof ( I've tried it for shits and giggles ) and it scratches. The glass would be my choice from a uv viewpoint. JMHO
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