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Thread: Window on the bottom of a boat?

  1. #1

    Window on the bottom of a boat?

    My uncle is retired and lives most of the time on a small coastal village. So he bought a small boat (7-8 meters long) a few years ago and is enjoying it. Since we are in the acrylic products business, he asked me to make an acrylic window on the bottom of his boat. It's not impossible with a 15-20mm thick clear acrylic piece with the dimensions of about 1x1 m, but I don't know anything about boat construction, yet common sense tells me that the acrylic won't be able to withstand the weight and pressure. And then there's the problem of impermeability. What's your thought on this subject? Is it even remotely possible?

  2. #2
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    We'll need a lot more detail on the form and construction of that boat hull before even considering some reasonable suggestions... If you do elect to proceed further, make sure you're planning to use Polycarbonate material as opposed to regular acrylic, a brand name that comes to mind is Lexan. Another potentially problematic concern around the marine environment is sunlight, particularly ultraviolet wavelengths over the long term, which have a profoundly degrading effect at the molecular level on all organic chemistry.
    Last edited by Morey St. Denis; 02-20-2013 at 6:58 PM.

  3. #3
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    Silver Springs in Florida offers glass-bottomed boat tours... you can REALLY see to the bottom of the springs on those tours.
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  4. #4
    You might want to try getting in touch with John Blazy. He's got a lot of experience with building boats with "glass" bottoms. See his site

    You can see one of the windows on the boat he calls Calypsee


    He's got an interesting method for filling the weave of fiberglass with epoxy, too. You can see the epoxy on the left in this picture.


    This shot is from when he was building the boat, above.

  5. #5
    It is entirely doable. There was an article in one of the Gougeon/or epoxyworks issues. I don't think it is one of the ones online, but they will send out old copies free, and they have free tech advice, best to phone in for that. WEST system epoxy folks.

    Normally this is done with a flat bottom often plywood boat (for home builders). You use a small window say 16 to 24". 1/4" lexan. you insert a flange of plywood around the hole, and glass in the flange so it is strong and water resistant. You caulk the window to the flange with 3M 5200. You then insert the window flush, and fasten it in place with a lot of small SS bolt sets, 1-2 inch spacing.

    This is basically the same process by which windows are installed in boats, and descriptions of that are a good starting point. I am talking here the method by which ocean capable windows are installed, not just pleasure onshore cruisers. The main departure is that the simple method for doing that has the window mounted on the surface, not recessed, but in this case you need to make stuff so it is relatively smooth to the water flow.

    It may sound light, and I am not offering structural advice. But consider, skiffs often have a structure that is nothing more than 5 mm doorskin/underlayment plywood, with one layer of 4mm fiberglass cloth. often around 42" wide. One would never make a trap door cover in a floor, or a floor itself, that light, but it is "completely safe" in a small boat because the water pressure counters the loading in the boat, though that loading is not uniform.

    Imagine a 7 foot x 42 inch dingy, that boat might have a wetted surface area of say 25 square feet (guess), and it and the person within, might weight 250 pounds. so the pressure on the boat would work out to 10 pounds per square foot. That is a load that it is easy to imagine being supported by a tray shaped square foot of plywood. And in the boat situation, that square is what we call an element, meaning it is fully bonded in along it's perimeter, therefore very well supported. If you have rough wetted surface area, and displacement info for your boat, you can come up with the pressure on the panel. I would probably be satisfied to adjust the material thickness in relationship to the material stiffness, which is a third power thing. It would also be reasonable to simply stack sand bags on a panel, but you might prefer not to buy a variety of panels until you found one that passed. I would probably be happy to simulate the test with ply like occume. One often finds that boat windows and marine windows are the same thickness as the surrounding ply.

    All these kinds of rules of thumb assume one has a reasonable safe means of testing the boat in use. This is more possible with some boats that others. In safe water a sinking canoe is one thing, a sinking motor cruiser with people below is another.

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