Really, why not automotive quality glass?

[Pgutierrez]

Why should sailboat manufacturers use lexan type glass that crazed like crazy and not automotive quality glass that doesn’t craze? Is it the possible flex factor? Can’t they just engineer that part of the boat to not flex? Just asking...

[CaverCop]

Just pure speculation but I assume it is the flex and possibly the weight as well.

[Pizzazz]

I thought Lexan was good for hatches because of its impact resistance. Not only waves but also dropping a wrench while working on the mast... it will not break Lexan but it will break pretty much anything else. Also, I am not sure if automotive glass will survive a good wave. For side windows you can use pretty much anything including tempered glass.

[dkenny64]

weight...
glass is much heavier than lexan or plexiglass.


autoglass can be laminated or tempered..
tempered has to be cut to size and treated(heat annealed).costly..


-dkenny64

[BillKny]

There are (very generally speaking) three kinds of glass.

PLATE GLASS which is normal window glass, and shatters into large sharp pieces. It has no place on a boat.

LAMINATED GLASS, which is used for automobile windows. It is two layers of glass with a sticky plastic layer in between. It is not especially strong, but when broken the plastic keeps all the pieces stuck together so they are not dangerous.

TEMPERED GLASS a very strong heat treated glass that is quite resistant to breakage, but when it does break it shatters into a million tiny pebbles, mostly not very sharp.

Both laminated and tempered glass are not easily available in any size or shape since they can not be as easily cut as plate glass.

There are two kinds of plastic used in boat windows. “Lexan” and “Plexiglass” (AKA polycarbonate). Most boat windows are made of polycarbonate, not Lexan.

Both plastics are MUCH LESS susceptible to breakage from impact than even the best tempered glass. Since a broken port of ANY kind leaves a large and difficult to plug HOLE in the boat, this is usually considered a bad thing. Boats have sunk from this (see Winston Churchill 1998 Sydney Hobart Race)

If you have a houseboat on a lake, put whatever kinds of windows you want on it. If you are crossing oceans, ONLY good polycarbonate windows should be used. Anything else is substandard.

Lexan is “bullet proof” and if you expect to be shot at, use it. But it is more prone to scratching and UV crazing than polycarbonate, and offers no other real performance benefits.

Most windows that fail on boats do not fail from wave impact, as is usually assumed. Rather, it is the leeward side windows that fail, when a boat falls off a wave and free falls and then impacts the water below. Glass simple can not survive this.

[boatpoker]

Originally Posted by BillKny

Most boat windows are made of polycarbonate, not Lexan.

Lexan is a polycarbonate material.

[Jim Cate]

There are two kinds of plastic used in boat windows. “Lexan” and “Plexiglass” (AKA polycarbonate). Most boat windows are made of polycarbonate, not Lexan.

Lexan is a tradename for a brand of polycarbonate plastic and plexiglas is a trade name for acrylic plastic, also known as Perspex in some areas.

Jim

[Jammer]

Recently I replaced three operable portlights on my boat. They were 25 years old and the plastic was foggy and some of the the dogs were broken off, so they leaked.



The 7x15" and 4"x10" OEM portlights were plastic, made with an ABS frame and acrylic glazing.


New Found Metals makes some very nice portlights with stainless steel frames and 10mm thick tempered glass glazing. The 7"x15" ones are $349 each plus $40 for a screen for $389 total. They are CE rated. Though susceptible to impact damage they are very tough absent a collision, gunshot, direct hit with a hammer, etc.


I was able to purchase OEM plastic portlights for $131 each including the screen. This left me $780 to spend on something else. There is no doubt in my mind that the glass portliglhts would be better in every way but mine is a modest boat that I will only keep for a few years.


In general tempered glass can be ordered in any size and shape but must be cut before tempering, and then shipped, a costly process especially for small orders.



My boat also has some larger, non-operable portlights. They are made of acrylic and are curved. Curved, tempered glass is available but prices are much higher than for flat pieces and lead times are long.


In short the cost difference is significant. I suppose there are high-end boats that use tempered glass. I've never been on one.

[noelex 77]

Originally Posted by Pgutierrez

Why should sailboat manufacturers use lexan type glass that crazed like crazy and not automotive quality glass that doesn’t craze? Is it the possible flex factor? Can’t they just engineer that part of the boat to not flex? Just asking...

It is a mystery why so many boats use plastic materials for windows/hatches.

My only thought is the designers only sail new boats and don’t have to deal with the inevitable crazing and leaking that befalls these materials as they age.

Some of the better cruising boats such as Oyster use all glass in the windows, but hatches are still often plastic.

On our new boat we specified all glass windows. The hatches are a mixture of solid aluminium and or aluminium/glass so it is possible to avoid plastic, although glass hatches are expensive.

[GordMay]

Originally Posted by BillKny

... There are two kinds of plastic used in boat windows. “Lexan” and “Plexiglass” (AKA polycarbonate). Most boat windows are made of polycarbonate, not Lexan ...

In case anyone missed it:
Lexan is a brand name of polycarbonate, whilst Plexiglass is a brand name of acrylic (both plastics).

[Fuss]

Originally Posted by BillKny

Most windows that fail on boats do not fail from wave impact, as is usually assumed. Rather, it is the leeward side windows that fail, when a boat falls off a wave and free falls and then impacts the water below. Glass simple can not survive this.

But why can’t glass be used, it just has to be thick enough, I’m guessing 15mm+ for modern sail boat larger side windows. Oyster for example.

[Fuss]

Actually, on thinking about it, maybe 20mm+ would be better.

[250224]

Originally Posted by noelex 77

On our new boat we specified all glass windows. The hatches are a mixture of solid aluminium and or aluminium/glass so it is possible to avoid plastic, although glass hatches are expensive.

Did you specify isolated glass, i.e. have a protection against the cold?

Where can one get good strong quality glas (in northern Europe)? I know Ertec in Denmark but didn't yet ask.

[Fuss]

very good question, also it would be good to know the thickness

[GordMay]

Glass is much heavier, less flexible, and much more difficult/expensive to shape (curve), than plastic (polycarbonate &/or acrylic) glazing.
Why would one choose to use it?