Which Boat Window Materials?

[Cuttyhunk1981]

Hi,

I need to replace the cabin windows on my 44ft sail boat as they are very badly craised. I am not sure which material to go for and have been told there are three main options perspex, polycarbonate or strengthened glass.

My understanding of the comparison between each material is that perspex is more scratch resistant then polycarbonate but polycarbote is tougher then perspex and won't crase as quickly and glass is great because it doesn't scratch as easily and looks great but isn't as tough as polycarbonate.

Does anyone have any opinions on the best cruising boat window material to use?

Thanks Anthony

[dannc]

Here are the Dashew's thoughts on glazing.

SetSail» Blog Archive » Glazing

SetSail» Blog Archive » Glazing Question

Later,
Dan

[UNCIVILIZED]

You can get laminates which provide something of the best of each to some degree. Meaning various types of tempered glass, either type of plastic. And if you go with Polycarbonate, definitely get the scratch resistant coatings... Rohas I believe it's called.
Or you can get a set of ports made of a couple of types of plastics laminated together & call it good. Such is sometimes done on BIG opening, foredeck hatches on racing yachts.

There are a couple of other factors to consider on what you choose. How are you mounting them, as with some climactic/temperature variations, some of the plastics will expand & contract enough to break the bond of the sealant/adhesive. Beth Leonard mentions Polycarbonate doing this, & that because of it, they switched to tempered glass.

Also, Polycarbonate, & to some degree, Acrylic both absorb moisture with time, & suffer from UV degradation. Both of which actually can cause quite severe strength losses, so talk to the manufacturers on this.
Some of those folks hiding behind "bullet proof" Lexan (polycarb) could be in for a rude surprise if anyone takes a copper jacketed, lead cored, poke at them. Seriously.
And said info comes from a gent who's a premium expert in the protection field.

I think that if you look at a lot of the commercial vessels, you'll see that their standard windows are tempered glass. And that the heavy duty, storm shutters/windows, made out of lexan only get bolted on when they're going to be facing serious heavy weather. Albeit some of the latter are plywood too.

Also, be VERY careful in terms of what you use sealant/adhesive wise for non-glass windows, as some sealants can chemically/molecularly damage the various plastics used in some types of windows & ports. For things especially with (metal) bolt on rings, butyl tape has really caught on it seems.

For me, if it's time to seriously go offshore, & I'm re-doing the ports. I'd go with a heavy duty set of Acrylic windows bonded in place. And then, on the cabin, above & below the windows, glue on a nice wide, solid strip of G10. To which (clear) storm windows/shutters would be bolted most of the time. Likely some thick Polycarb, possibly with sacrificial, peel off layers of clear "tape", or a thin layer of Acrylic bonded to the outer side of the Polycarb for scratch protection.

And when I say sacrificial layers of tape what I mean is almost exactly that. While I haven't researched it, it's common to see race car drivers have their pit crew pull off a thin layer of tape off of the visors on their helmet, when they make a stop. It's a quick way for them to get 100% clear vision back in 1/2 sec, as with the old layer which gets tossed goes all the oil, grime, etc.
But sans research into the pros & cons of that, or just to go KISS; storm over shutters like I mentioned, of laminated, or bolted together Acrylic & Polycarb.

Ah, also do some looking into what to use & what not to as far as cleaners on plastics. I'm going on memory here, but I seem to recall that Windex & Ammonia products are a no no for Lexan, as it'll soften the material even more than it is to begin with. Possibly even causing a strength loss... do some Googlefu on this.

[Matt Johnson]

We replaced our deadlights with a 5/16" tempered glass, but kept the old Plexiglass ones as a storm shutter. Amazing the difference it made actually being able to see out of your widows!

Matt

[jr_spyder]

This past spring I had the same issue and did a lot of research. I have six fixed hull windows that go below water when the boat is heeled over. So they have to hold back the ocean. After 26 years the original 1/2" Lexan windows started to leak around the edges although their strength still seemed perfectly fine. In fact I had to abuse them severely to remove them and they never broke. They were very crazed and dull. What had failed was the sealant between the plastic and the fiberglass cutouts in the hull. When I took everything apart it was clear that the sealant they used way back then was happy on the fiberglass but not the plastic. The sealant came off the plastic cleanly and easily, but was still very stuck on the fiberglass.

With some advice from the local Hinckley yard where my Little Harbor was built I found the local location of Piedmont Plastics Piedmont Plastics who were extremely helpful. There are all sorts of choices of polycarbonate, the one used mostly on boats being Makrolon (their brand name, other companies make competing products). They also have different coating for UV, scratch resistance, etc. The local shop didn't have in stock what I needed but found it elsewhere, put the order together for my cuts and had it delivered to my house in 2 days. I was amazed.

Once I had the six rectangular new pieces I had to machine them into ovals to match the old ones. This was dead simple with a router and normal woodworking bit. The plastic was very easy to work with.

As mentioned previously the key is the adhesives. Luckily the technology has vastly improved over the years. Again with advice from the yard I found Sikaflex has a broad selection of products and an excellent web site for learning what to do. They have a specific primer for fiberglass, another one for the polycarbonate, and of course the adhesive that goes between. All great stuff and easy to use with very clear instructions and videos. They also have solutions for glass and every other material you may want to glue up it seems.

My hull windows are now perfectly clear and leak free. I have to admit to having a bunch of apprehension the first few times we heeled the boat over into some pounding waves but no leaks. I don't give it any thought now.

My favorite part of this story is that the yard estimate for this work was $6 to 8k! I did it for around $400 in materials and a bunch of hard but fun work. I also have the confidence now to start replacing all my polycarbonate hatch glass next winter. All my frames are good so just the plastic needs replacing.

All this being said your best solution might be tempered glass - which I know nothing about.

Good luck.

JR

[Matt Johnson]

I forgot to mention that we used Dow 795 structural adhesive for the tempered glass. It's the stuff used to hold the huge windows up on skyscrapers.

[a64pilot]

I've been thinking automotive "safety glass", which is of course lamintaed glass. Tempered glass of course is used on all windows of a car except the windshield, tempered glass breaks into tiny chunks as opposed to a big piece and that is why it's used I believe, but in the windshield where absolute strength is required, I believe laminated glass is used.
I think laminated glass is a little more expensive, but much less likely to fail from an impact?

[a64pilot]

double post

[Exile]

Originally Posted by jr_spyder

This past spring I had the same issue and did a lot of research. I have six fixed hull windows that go below water when the boat is heeled over. So they have to hold back the ocean. After 26 years the original 1/2" Lexan windows started to leak around the edges although their strength still seemed perfectly fine. In fact I had to abuse them severely to remove them and they never broke. They were very crazed and dull. What had failed was the sealant between the plastic and the fiberglass cutouts in the hull. When I took everything apart it was clear that the sealant they used way back then was happy on the fiberglass but not the plastic. The sealant came off the plastic cleanly and easily, but was still very stuck on the fiberglass.

With some advice from the local Hinckley yard where my Little Harbor was built I found the local location of Piedmont Plastics Piedmont Plastics who were extremely helpful. There are all sorts of choices of polycarbonate, the one used mostly on boats being Makrolon (their brand name, other companies make competing products). They also have different coating for UV, scratch resistance, etc. The local shop didn't have in stock what I needed but found it elsewhere, put the order together for my cuts and had it delivered to my house in 2 days. I was amazed.

Once I had the six rectangular new pieces I had to machine them into ovals to match the old ones. This was dead simple with a router and normal woodworking bit. The plastic was very easy to work with.

As mentioned previously the key is the adhesives. Luckily the technology has vastly improved over the years. Again with advice from the yard I found Sikaflex has a broad selection of products and an excellent web site for learning what to do. They have a specific primer for fiberglass, another one for the polycarbonate, and of course the adhesive that goes between. All great stuff and easy to use with very clear instructions and videos. They also have solutions for glass and every other material you may want to glue up it seems.

My hull windows are now perfectly clear and leak free. I have to admit to having a bunch of apprehension the first few times we heeled the boat over into some pounding waves but no leaks. I don't give it any thought now.

My favorite part of this story is that the yard estimate for this work was $6 to 8k! I did it for around $400 in materials and a bunch of hard but fun work. I also have the confidence now to start replacing all my polycarbonate hatch glass next winter. All my frames are good so just the plastic needs replacing.

All this being said your best solution might be tempered glass - which I know nothing about.

Good luck.

JR

Helpful post, and I've bookmarked Piedmont Plastics. I've also been researching the best materials & sealants to use for the hatches & ports on my 28 year-old Bristol.

After consulting with a local yard, I finally chose tinted Lexan and LifeSeal (made by BoatLife) for the sealant, and just got done replacing three hatch lenses. Like the ports on your LH, I believe my hatch lenses were original and made from Lexan. I contacted Bomar/Pompanette and my 16 opening portlights, however, appear to be made from acrylic.

I get confused with all the different brand names for polycarbonates and their various pros & cons, but is Makrolon the same as Lexan? I've been told that Lexan is stronger than acrylic but less scratch-resistant. In your case, did you wind up replacing your port lenses with basically the same Lexan the factory used, albeit with a better sealant system it sounds?

Thanks for a most helpful post.

Dan

[jr_spyder]

The material choices are definitely confusing. The old Little Harbor guys (it's great they are still around and very passionate about the boats) told me the original material was Lexan but they use Makrolon now. Don't know why. Because I found a local supplier it was an easy choice. The one surprise is a huge difference in price for coatings/treatments. The abrasion resistance doubled the price for example if I remember right. More for UV protection too. That being said my sales guy didn't insist I get the treatments and said most people don't and never come back with problems.

I don't know what I'll use when I get to the hatches but Makrolon will be a strong choice. But these get walked on so abrasion resistance is far more important than the hull ports. I also think the sealing of the plastic to metal on the hatches will be easier and cheaper than the critical strength needed for the hull ports.


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[Cparharris]

I just replaced all my plexi on the dodger with Makrolon. Much clearer than anything else I have seen.


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[Roy M]

I replace my acrylic fixed ports every 12-15 years, whether they need it or not (little joke, there). In a few years I will be on my fourth set. For me, acrylic was (and still is) the most simple, cost effective and lightweight option. I combine the port replacement with the LPU painting schedule to reduce the work.

Polycarbonate gets cloudy with UV, Acrylic crazes (for me, not a serious issue during its lifespan), glass is too expensive, too heavy, and leads one down the path that waits for leaks to happen rather than preemptively replacing and rebedding. Also, I like having dark tinted portlights.

Mine have a fixed inner rim, with a matching outer finish ring. I flame polish the outside edge of the acrylic to eliminate any potential cracking caused by the jigsaw blade, then bed everything in 3M 4200 UV, cover the exterior rim screw heads and finish with a coat of LPU to the margin of the cabinside.

[rocksculpter]

Lexan is impact resistant where the acrylic shatters but not as good optically. I've found that carefull cleaning with a soft rag, old diaper, prevents scratches. I'm replacing the fogging tempered glass on all my ports after a test on one port that is doing weel after more than 5 years.

[DennisDW]

Tempered glass, 1/4". It's cheap and readily available. I have it in my dodger and fixed portlight windows. I second the use of dow glass adhesive. My dodger took the impact of a large, metal winch handle that was flipped out of the main halyard winch by the jibsheet. It was violently slammed against the glass and bounced off and into the sea.

I most like the clarity and longevity. It will never craze or get cloudy. Doing the job once is good. My new hard dodger will be glass. An important point; the edges must be protected (for the heat tempered version) but then that's usually no problem as that is how we mount it. There is a Youtube video of chemically tempered glass on an hydraulic press the bends it 45 degrees with out failure.

https://www.youtube.com/watch?v=oRSsgwefD-4

This just blows my mind.

Good luck,
Dennis

[avb3]

Just came across this on a hunting forum, where a similar issue is being discussed.

The product suggested was MarGard.

Is anyone familiar with this or have any experience with it?