Replacing plexiglass windows

Discussion in 'Metal Boat Building' started by luso, Apr 18, 2007.

  1. luso
    Joined: May 2006
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    Location: florida usa

    luso New Member

    Hello, we have a 50 ft steel hull sailboat and are refitting the whole boat. We are starting the replacement of all the windows at the moment and we are wondering if we could have some help from you guys. The amount of windows are as follows: 10 windows in the saloon and 4 in the cabins. The material that was there was 1/2 inch plexiglass and because of the curves on the boat where the windows go we want to stick with the same. We have been researching to find companies that deal with this size plexiglass and were only able to find one company in Miami that sells it. We got some samples but it seems like they scratch very easily but when we asked the salesperson they said that there were no other choices unless we change to a different material. We have read about the difference of using lexan and tempered glass but we would like to use the best quality plexiglass if possible. We have also read that cell cast plexiglass is the higher quality plexiglass that is available. We are wondering if you know of any companies that work with such material in our area. Miami/Fort lauderdale.
    We appreciate any comments that you have to offer. Thank you very much, Luso
  2. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Can't suggest any companies in your area, no. But if scratching is a concern, the Lexan (polycarbonate) is considerably stronger and harder, ie. more scratch resistant than the Plexiglas (acrylic).
  3. Rusty Bucket
    Joined: Feb 2007
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    Location: florida

    Rusty Bucket Junior Member

    Plexiglass Fix

    Hi, Did you know that you can buff out acrylic plastic much like you would polish dull paint? If your problems are just surface scratches and hazing you might try a electric buffer and a very fine polishing compound like " silk cut". Replacing acrylic windows that thick is going to be expensive so I would try a few things to restore them first. Acrylic sheet can be formed using heat from somthing like a heat gun or propane torch so you might try that. good luck, rusty
  4. bighouse
    Joined: Jul 2004
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    Location: TN

    bighouse New Member

    I would suggest researching the properties of polycarbonate before using it for portlights. It is harder than acrylic but probably not to a significant degree for this purpose. And while polycarbonate is exceptional at bearing impact point loads, its tensile strength, compared dollar to dollar, is about half that of acrylic.

    Polycarbonate is an excellent material if you expect to have somebody shooting bullets at your portlights, but if your portlights will have more conventional duties, acrylic would seem to be a better value by approximately twice. In 1/2" thicknesses, this stuff ain't cheap.
  5. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    Half inch is rare, though I once had a boat with a 1/2" plexiglass companionway hatch. It actually had a compound curve in it. I immediately reinforced it when I bought it with a curved mahogany bar! Then I met a guy who had the same boat, and he had broken his and had one made. $350.00 fifteen years ago.
    I gather your windows are crazed to the point of cloudiness. Good luck whatever you do. Real 1/4" safety glass is the best, but curves cost. Still compare, might not be as big a difference as you imagine. 1/2" plexi of good quality must be pricey.

  6. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Probably at least as important, long-term, as the strength of the plastic itself is how it's fastened to the frame. Neither acrylic nor polycarbonate will fare well under the horrific stress concentrations created where screws or bolts are drilled through the plastic. The frame's gotta distribute stress uniformly over the edge of the clear element or you'll get stress cracks forming.
    Where ultimate strength of the plastic would really concern me is when there's a risk of hardware, such as an anchor or spinnaker pole, breaking free of its normal place and coming at the glass. The loading here is a hell of a lot more than is generally anticipated by the rules- look at the 19mm windows on the new Dashew designs, for instance, as an example of what you get when you consider this possibility.
  7. riggertroy
    Joined: Jul 2004
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    Location: New Zealand

    riggertroy Senior Member

    I will be mounting Polycarb windows in a yacht I'm working on - the material was from offcuts from a job that a mate did - he recommended for my situation not drilling holes in the polycarb but using the original window surrounds that held the original glass windows in place.
    The weak point for me will be the securing of the windows in place - he demonstrated the strength of the polycarb on an offcut - swung a pickaxe at it and only a scratch was evident - the stuff flexed a bit when the pickaxe hit it. Mind you it was a glancing blow from a spinaker pole that smashed one of the old (40+years) glass windows.
    My 2cents worth...
  8. Jimbo1490
    Joined: Jun 2005
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    Location: Orlando, FL

    Jimbo1490 Senior Member

    The trick with mounting plexi in frames is to leave a gap around the entire edge proportional to the length and width, then center the sheet within the gap before securing the sheet with the fasteners, clamping frame, adhesive or whatever. This is the trick to avoiding the edge stress cracks. And if any fastener holes will pass through the plexi they must be oversize also to avoid edge stress. Plastics shrink and grow much more than metals, so if the glazing is in metal framing, you need to worry about this.

    The only advantage to polycarbonate is impact resistance. In every other way it is inferior. One of the worst things about it is its extremely poor chemical resistance. Many household detergent cleaners will cloud it permanently, it wont stand up to even the mildest solvent, and unlike acrylic, it is a bear to sand and buff out defects like scratches or clouding.

    If you must drill any holes in plexi, remember to buy the specially ground drill bits for that purpose, available at MSC, J&L and others. This greatly reduces the possibility of cracking during drilling. Also generously bevel (countersink) any drilled mounting holes.

    I know about this stuff since acrylic glazing is common on airplanes, which is what I work on for money most days :)

  9. U.S.A. Marine W
    Joined: Oct 2007
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    Location: Ft lauderdale

    U.S.A. Marine W Junior Member

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  10. Brent Swain
    Joined: Mar 2002
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    Location: British Columbia

    Brent Swain Member

    Lexan, polycarbonate is far less scratch resistant than plexi and tends to fog up totally in a couple of years in the sun. The hard surface available for lexan falls off like old varnish in short time leaving you looking thru foggy windows. Stick to plexi if you want to see thru them in a couple of years.
  11. Kay9
    Joined: Oct 2006
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    Location: Central Coast Oregon US.

    Kay9 1600T Master

    USA Marine windows is a good company. They did a buddies of mines fishing boat recently and it went very well.


  12. U.S.A. Marine W
    Joined: Oct 2007
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    Location: Ft lauderdale

    U.S.A. Marine W Junior Member

    Marine Windows

    We suggest if the curve on this sailboat is not to deep, we can try tempered glass. How long are the windows, because tempeed glass has a flexibility point when inserted in to a frame.

    U.S.A. Marine Windows Mfg inc.
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