Window Saga. New Thread. Small Question.

[Chotu]

I have my new poly carbonate windows floating in a frame. It’s working pretty well. I’m having just a bit of a problem.

This is the really good poly carbonate. The stuff I had from the beginning. Only in this geographic location do I have this problem and only in the morning as there is a really quick 50 degree change in the temperature of the polycarbonate. And this is what has torn the windows apart time and time again with Dow 795.

At night, it’s about 50° here. Maybe 60. Something like that. Very soon at 9 AM, surface of the poly carbonate heats up to probably 110°. But the inside of the windows is still cold. 50 or 60°. The temperature differential creates more expansion on the exterior of the poly carbonate than on the interior. This causes it to curve and bow out. It does this while it is also expanding more than a quarter of an inch in all directions from the heat.

Once the temperature differential goes away and the entire polycarbonate sheet is 110°, everything is good. It settles back down.

I have solved the expansion issues by floating the windows in frames. You can see the frames on the bottom and top of the windows in this picture. However, in areas where the windows meet each other, where there is a vertical gap between the two windows, I have yet to figure out how to hold that down. Because they want to bow out instead of squeeze up and down into the frames you see in these pics as they are supposed to.

How can I hold the middle of the windows down, in a vertical sense, so that the windows get taller and shorter as they expand and contract, instead of bowing out?

[Chotu]

I thought I would post another picture from inside to make it more clear. See? It is rising up off of the supports. There is nothing holding them in place yet. But I want to make the right move. I don’t want to do something wrong. So I thought I would get some opinions on how to best hold these down.

[Rob_P]

Commercial boat manufacturers don't seem to have the problems with their windows that you're having and their windows are equally as big or sometimes larger than yours.

It's possible that it's your windows which are the problem here and not the way you're trying to attach them.

[Chotu]

Originally Posted by Rob_P

Commercial boat manufacturers don't seem to have the problems with their windows that you're having and their windows are equally as big or sometimes larger than yours.

It's possible that it's your windows which are the problem here and not the way you're trying to attach them.

That’s because they are using glass. This is poly carbonate. I want to use it because it weighs significantly less. I’m looking for ideas on how to capture it. Not how to change materials, please.

Basically, what I have come up with so far, is 1) some sort of H shape channel to go between them, held by the adhesive Thais holding the J channel

2) stuff a bunch of 795 under them, but that won’t work because it will peel it, or

3) put a screw in the middle of each one. But that won’t work either. Because they need to expand and contract.

[Chotu]

And I should add the entire rest of the boat is fine. Only this part which receives the morning sunshine facing east has trouble. I never ran into this before because I didn’t use a dock.

The increase from 50 or 60° to 110° in the sun it’s a lot in an hour or so

[Chotu]

And now that the interior and exterior temperatures are closer, they settled right back down.

[Narfi]

An aluminum H channel secured to the frame?
A composite H channel?

Over sized holes and large area decorative washers? (I don't think it would look as good here though ;/ )

That is a lot of expansion.... Do your upper and lower frames offer enough room?

[Narfi]

Knowing the expansion, you could control where it goes with slotted holes and screws around the parameter.....

At minimum size the screws are in the outer edge of their slots, when it expands to its max, the screws are at the inner edge of the slot and going each way guides it to prevent expansion from all going to one edge or corner as well as guiding it back to its happy place when done...... seems you will need some sort of VERY flexible and resilient sealant if you have any hope of keeping it sealed though.

[Westcliffe01]

You should use the channel to control all edges. It looks like you have plenty of structure to attach the channel to on the vertical seams. you might just need to trim a tiny bit of material off the edges of the panes to make enough space.


Maybe next time you could get a groove CNC routed into the surface of the glazing to hold a PTFE O-ring with some squeeze preload, which could seal on the channel you provide, it would then be more leak tight, even with the expansion. As far as I know all O ring material can be obtained as continuous lengths.

[rslifkin]

I agree, channel on all 4 edges is the answer.

[Chotu]

Originally Posted by Narfi

Knowing the expansion, you could control where it goes with slotted holes and screws around the parameter.....

At minimum size the screws are in the outer edge of their slots, when it expands to its max, the screws are at the inner edge of the slot and going each way guides it to prevent expansion from all going to one edge or corner as well as guiding it back to its happy place when done...... seems you will need some sort of VERY flexible and resilient sealant if you have any hope of keeping it sealed though.

That’s a thought I never had. That’s a good one. I like the H channel a little better, because it will look nicer, but it would be possible to have slots and screws. I never even thought of that.

They don’t leak now, because the rain just goes over the top frame, down the window and off the boat.

When it’s raining, the damn sun that causes them to lift is gone and they are cool so they lay flat and no water gets in.

[Chotu]

OK. I guess the channel wins out. Maybe I can try with the H channel.

Then on the very end just use the normal J channel that I have.

I think this is going to work. And it’s nice to have not even half the weight of glass.

[Westcliffe01]

Did the supplier not offer white for the edge masking ? That black trim tremendously increases the heat stress.

[Chotu]

Originally Posted by Westcliffe01

Did the supplier not offer white for the edge masking ? That black trim tremendously increases the heat stress.

There is no supplier. I did everything.

I realize Black increases the heat stress tremendously. But also, I have a look to a accomplish.

[rslifkin]

There's always the half-joking worst case answer to reducing the heat stress: Some kind of fan setup to blow a bunch of air across the windows to cool them when a significant heat differential is detected. I wouldn't actually recommend doing this, but it might work...