New windows! Glass or polycarbonate on piloto house?

[carlo de leo]

Hi All!
After 23 years, its time to change the polycarb's of my pilot house. The biggest problem is that it's a convex two axis single piece (a really art work of PO), see pictures attached.
Now, I have the opportunity to make it a 3 pieces windshield...or not. And also make it in tempered glass...or not.
The whole windshield has 75cmX215cm. In 3 parts, it would be 3 times 75cmX75cm in average.
I'm not planning use any screw to fix the new one.
So, what do you think about the material and 3 parts or 1 single windshield?
thanks!!
Fair winds,

S/V Gulliver

[Matt Johnson]

I can't imagine being able to get the curve in glass done reasonably, but if you're able to, get glass. It's so much nicer not having to deal with scratches and having perfect optics. Just make sure it's up to the strength needed for your sailing.


Matt

[carlo de leo]

Originally Posted by funjohnson

I can't imagine being able to get the curve in glass done reasonably, but if you're able to, get glass. It's so much nicer not having to deal with scratches and having perfect optics. Just make sure it's up to the strength needed for your sailing.


Matt

Thanks Matt,

Actually, to make it in glass, I'd have to make it convex in just one Axis and rebuild the wood support inside. It's not a difficult job. It's possible to make any constant curve desired with glass (one axis/radius) in a computerized furnice.
I'm just not sure about resistence.

[Matt Johnson]

On our last boat, I converted the side deadlights to 1/4" tempered glass and loved them. Very cheap to have done in Guatemala, but doubt they would do any curve.

What thickness is the polycarbonate now?

Matt

[zboss]

The other advantage to glass is the ability to apply a invisible UV and heat barrier layer to the glass.

[carlo de leo]

Originally Posted by funjohnson

On our last boat, I converted the side deadlights to 1/4" tempered glass and loved them. Very cheap to have done in Guatemala, but doubt they would do any curve.

What thickness is the polycarbonate now?

Matt

I estimate +/- 8mm

[carlo de leo]

Originally Posted by zboss

The other advantage to glass is the ability to apply a invisible UV and heat barrier layer to the glass.

Yes that's the idea. have a full transparent glass and aply a filtre layer

[carlo de leo]

And do you think about 3 pieces versus 1 piece?

3 pieces: if one broke- less damage. More dissipation of forces. But more area for leakage.

[estarzinger]

Glass is just way way superior in almost all regards (except weight). If you can do glass, do it. If you are going to do 'serious sustained' offshore work, I would suggest 10mm tempered. That thickness is a bit heavy, so for more casual sailing you can get away with thinner.

We originally had glass on our hard dodger and polycarb on our side windows - later switched the polycarb out for glass. The glass lasted 'forever', including the seal, where as the poly got less clear and broke its seal (because of greater thermal expansion).

[UNCIVILIZED]

The curves built into the current glazings add significantly to it's strength & stiffness, perhaps on the order of 200%. And most likely they contribute directly to the strength of the pilothouse as well. So I'd not consider switching to flat glazings without first figuring out if you'd need to significantly beef up the structure supporting them, that they're bolted to. I'm not saying that the proper type of glass won't work in this application, but to check first.

The other thing is that while it relatively easy to thermoform plastics, glass is another matter entirely. Especially glass rated for severe impacts. Which of course means that it can be quite expensive, if not fully prohibitively so. And I'd think that if glass isn't perfectly molded on the 1st try, one might have to start over with some fresh stock. Though I can't say for certain.

On this issue you might query Evans Starzinger, an advisor here. As he & Beth Leonard switched the glazings from lexan (polycarbonate) to glass, due to the amount of expansion in the polycarbonate from temperature changes.

Also, I'd be curious to hear about what you learn, if you'd be so kind. Ditto on what you choose in terms of glazings to use.

Ah, one other thing is that polycarbonate can & does lose a fair bit of it's strength over time due to moisture absorbtion, & UV. So choose it's thickness accordingly, after researching this issue. And there are plenty of coatings which greatly mitigate or prevent the UV issues. Ditto on improving it's scratch resistance, hugely.

There's some good information on all of the above topics, & more, in various back issues of Professional Boatbuilder magazine. And another avenue of study would be the use of armored & impact rated glazings in VIP & Military vehicles, as well as aircraft. For obvious reasons.

[Privilege]

My advice...DO NOT use polycarbonate. Polycarbonate (aka Lexan) is not very UV resistant and will cloud over irreparably within a year, even if you cover it with a mesh material. (Ask me how I know). Lexan also scratches fairly easily. Most of the manufacturers (including my Privilege) use Acrylic. They look the same but are very different. Acrylic is inherently UV resistant. It is incredibly strong, between 4x - 8x stronger than glass but unlike Lexan, it can shatter so it is preferable not to make small screw holes in it. The trouble is that acrylic cannot be easily bent by more than a few degrees and must be heated in an oven before you do so. This is not an issue if you make the glass into separate flat pieces.

Your windows don't look too bad. If you are changing them for cosmetic purposes, you might want to consider sanding them. I know, it sounds scary but varying grades of very fine paper and a polish can bring them up as new.

[mikereed100]

Another vote for glass. I used 10mm tempered safety glass for the windows on our cat and, while they are way heavier than I would like, they are crazy strong and look brand new after 7 years of hard use. I once replaced a tinted window with clear and, as an experiment, tried to break the old one. I beat on it with a sledge hammer until my ears rang and only succeeded in breaking the side that was lying against a brick curb. The window remained intact and I didn't even know it had broken until I turned it over.

I used the Australian Transport Advisory Council Uniform Shipping Laws Code to determine the thickness required for my roughly 2' x 3' windows and came up with 5mm, although they recommended going no thinner than 6mm. Paranoia led me to use 10mm.

I like acrylic as I can work it myself but the coefficient of thermal expansion is such that it its hard to keep large windows from leaking as they expand and contract with temperature changes. Also, one must be very careful when cleaning them to avoid using cleaners that can cause crazing or clouding. They are much more prone to scratches as well.

Polycarbonate is a non-starter for me due to the clouding and scratching issues. I don't know if any of the coatings available, such as Marguard, are effective in preventing this.

[Terra Nova]

Originally Posted by UNCIVILIZED

The curves built into the current glazings add significantly to it's strength & stiffness...most likely they contribute directly to the strength of the pilothouse as well. So I'd not consider switching to flat glazings...

This.

Duplicate the original construction and material...exactly.

[zboss]

Four years ago we ended up going acrylic. Despite all the warnings about plastic we have yet to see any scratches, UV degradation, leaking ports, or cracks. If we were to develop one, we keep four additional replacements on board.

[Matt Johnson]

Being a pilothouse, visibility from the inside helm is extremely important. We put 1/2" acrylic on the new boat as our windows sit proud with no frames and I wanted to be able to through bolt, but even brand new, the clarity isn't the same as glass..... plus, no ability to add a windshield wiper.

Matt