Glass bottom boat

Discussion in 'Boat Design' started by Deep6lue, Aug 26, 2019.

  1. Deep6lue
    Joined: Mar 2018
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    Location: Mumbai

    Deep6lue Junior Member

    Hey all,

    Anyone with experience in building glass bottom boats? They are used for recreation in coastal reefs. Need info on the glass panel (Standards, Class rules etc.,)

  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I have designed several glass bottom boats and I have the regulations that I have applied, the calculations made and the corresponding drawings, but it is all in Spanish.
  3. Alik
    Joined: Jul 2003
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    Alik Senior Member

    There is no special standard. Glass is calculated as any other material, as panel for normal pressure. Important is a 'trunk' around glass bottom area, so if it cracks there is some 'freeboard'.
  4. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    In Spain there is a regulation dictated by the General Directorate of the Merchant Marine, specific for the placement of glass bottoms. The calculations I carry out by means of the direct calculation, applying the Timoshenko plates theory, for rectangulars panels loaded with a uniform load, perpendicular to its plane, with the condition that its deflection is less than the thickness of the material.
    The freeboard interpretation of something that is submerged would be worthy of a separate thread. Even if there is a coaming, the compartment will flood.
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  5. Alik
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    Alik Senior Member

    Or can use ISO12216, take design pressure from bottom. This is what we did.
  6. gonzo
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    gonzo Senior Member

    In general you wold use tempered or toughened glass. Laminated glass is an option, but usually more expensive. How deep is the bottom of the boat? I suppose it won't have any considerable slamming loads.
  7. TANSL
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    TANSL Senior Member

    NO. No glass at all.
    None. There is no slamming at the bottom of a displacement boat at low speed (less than 15 knots).
    Why doesn't everyone talk about what he knows?
  8. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Glass bottom, or viewing areas in the hull bottom, are outside the scope of normal rules.
    They are allowed, with caveats, as we did one many years ago. But you need to establish what design criterion will be applied and any subsequent mitigation.
    Special consideration is given the the fixing and thickness and type of glass and since it is a non-standard feature - it must be proved by hydrostatic test.
    jehardiman likes this.
  9. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    Adding a pressure bearing viewport to structure is one of the hardest things to do. Not only must you ensure that the glass/acrylic will bear the load, but you have to ensure that structure will support it properly as it expands and contracts ( believe me it will at a much different rate than the surrounding structure). There are some guidelines mostly built around medical, aerospace and submergence standards for "pressure vessel human occupancy" (PVHO). Generally for "low pressures" like a glass bottom boat or an oxygen chamber there will need to be a well supported rigid frame larger than the window on the low pressure side. The window is then set in an elastomeric material (with or without high dura standoffs) to prevent point loading. A second seal and a capture ring are added to the pressure side. As TANSL said, you will need to consult with your local regulatory agency if this is a commercial application, YMMV.
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  10. NautiPhillip
    Joined: Aug 2019
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    Location: Seabrook, Texas USA

    NautiPhillip Junior Member

    Hi Deep6lue,

    If this is intended for personal recreational use, I will share an experience that may be beneficial. Many years ago I worked at a very large sign shop that was clearing out old inventory. I bought 2 large sheets (1/2" x 10' x 4') of clear IR resistant Lexan and a number of large scrap pieces of the same.

    We knew that Lexan was slightly flexible but very strong, so being the country boys that we were, we took a scrap with us when we went hunting and at the end of the day, set it up for target practice. The scrap was about a 2' x 2' square of 1/2" thick Lexan. We shot it with a 30-30 carbine to no effect. Then a 30.06 and finally used a 7mm magnum, but we barely scratched it. The only firearm that did any real damage was a 12 gauge shotgun. The pellets were hot enough and slow enough to melt their way into the plastic. But nothing broke it or even cracked it. So we had an idea!

    My friends and I constructed a walk-in oven of studs, plywood and fiberglass insulation and used a propane heater, a commercial fan and an oven thermometer to monitor the heat. Then we made a cutout form. It was plywood with a hole cut out in the outline of the boat. The idea was that the heat would make the Lexan sheet 'sag' into the hole and the result looked more like a jet plane cockpit than a boat, but it was adequate to our purpose. We simply cut off one end of the 'boat' and the excess away from the 90 degree edge at the top of the form and left about a 3" lip.

    We then started cutting pieces of scrap and fashioned a keel, a transom, a couple of bench seats and a second layer of Lexan to apply to the gunnels; all of which we welded together using Methylene chloride and some wood clamps. We ended up with a 9' skiff that would seat 4 comfortably and it was made entirely of Lexan. The entire boat was transparent. Well, we did add some old stainless steel oarlocks and a few eyelets; one at the bow and two on the transom. But that was it.

    In retrospect, I would suggest some clear office mats to protect the seats and where you place your feet. Ours got pretty skuffed up over time. But we caught a lot of fish in that boat and it lasted through years of abuse.
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