Chapter 4: In Which We Battle the Evil Windshield (or “Plexiglas Madness”).
The normal approach on this boat project has been to a) look at an item that needs repair and determine how it previously functioned, b) read about it through books and the internet, c) talk a bit with the local experts, d) formulate a repair plan, e) do the repair and then, when it didn’t work or wasn’t quite right, f) do it again. This was the approach with the windshield, and then some.
The old windshield was a 1/4-inch acrylic in about three broken pieces. It was bolted into the frame with 3/8 inch bolts and square head nuts that were now completely rusted out. After removing the framing and shield, we put it back together to use as a template. I bought a 4 x 10 piece of 1/8 inch acrylic from the local plastics supplier. This length was longer than their standard 8 foot length, so I paid a bit more, but it was still fairly cheap at $60 a sheet. Instead of having them cut it in half, which would incur an additional charge, I just took the whole thing, and subsequently had enough for two – just in case. It wasn’t as thick as the previous shield, but in my non-scientific reasoning I had determined this was okay, because there was not a lot of weight that it was holding up and it didn’t need to be super-high impact resistant because the boat would be moving at such low speeds. I cut it using my neighbor’s very nice jigsaw. With the right settings and blade, it cut perfectly with no chips or cracks.
The windshield was a wrap around style, so the ends bent around the corners of the front of the boat. Bending acrylic can be done cold, or with heat (thermo-forming), depending on the thickness of the material and how far one wants to bend it. There are a whole set of equations to work with to figure how far the material can be bent cold or hot. Generally speaking, the thinner the material and shorter the bend, the better the ability to cold form. Conversely, thicker material and sharper bends require thermo-forming, and more concern about the breaking point. Logical.
But I have never been one to put much weight into mathematical equations, so I just decided to cut it to the right size and cold bend it in. To the point, it broke as soon as we tried to get it around the corner. I had the second half of the piece, so I wasn’t deterred at all. While there was quite a bit of time spent staring at the windshield frame, there still were no mathematical equations involved, no sir.
I did a little more reading, bought a heat gun, cut a new shield and began thermo-forming the bends. This is a fairly precise exercise in that it requires heating up the acrylic enough to bend, but not so much that it would sag, bubble or discolor. In an afternoon I had a nice new windshield – and in about 10 minutes of attempting to install it, I had two broken pieces of windshield. And this time, I must admit, I did feel somewhat deterred.
I did a third, and got this one installed all the way to the bolts secured with rubber washers and a lock nut. It cracked too. Even writing about it makes me tired and grouchy.
The new plan is polycarbonate: 30 times stronger than acrylic, and 3 times as expensive. I’m not screwing around this time. I’ve already downloaded the technical data sheets from the GE polycarbonate website (they make polycarbonate by the Lexan trade name). I am, however, at this time, in the midst of a windshield hiatus.
