Superstructure Techniques

Discussion in 'Boat Design' started by DianneB, May 23, 2010.

  1. DianneB
    Joined: Jan 2010
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    Location: Manitoba

    DianneB Junior Member

    I have a 21 foot aluminium Sylvan I/O bow rider that I plan to turn into a cuddy next winter.


    I plan to pull the windshield/helm back 24" and up and made the cabin roof 12" to 18" above the deck.

    Weight isn't a major issue but it does have to be modest.

    I would like the cabin to be bolt-on, have a roof strong enough for someone to stand on, and have open-able windows along the side and a hatch for quick access to the anchor cleat.

    It is highly desirable to have all corners radiused including the compound radius at the front-top corner (which is a BEAR to do)!

    What I am undecided about is the method of construction....

    I could use a steel frame (rectangular tube), which I can cut, shape, and weld easily, with steel sheeting over top. Inexpensive and easy but not the nicest to maintain.

    I could use aluminium plate (which I DON'T have the facilities to weld). More expensive but less maintenance.

    Or I could use moulded fibreglass over a steel or aluminium frame, a technique I have done before but requires a LOT of work.

    What are your thoughts?


    Attached Files:

  2. TeddyDiver
    Joined: Dec 2007
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    Location: Finland/Norway

    TeddyDiver Gollywobbler

    I'd go with ply and glass.. Here's one way to do it. It leaves you with straight sides and top but is easy and fast. Cut the sides out of ply, put them on a flat surface covered with plastic (anything that works as a release film will do), the top in the middle and each side around it apart as much as you want radius in the corners. Cut glassfiber rowing a bit wider than the space btw the panels. Wet the gf with epoxy, set the panels on top of them and add some weights. To get the side corners rounded same way it needs to cut a corner of another of the facing panel sides. These cuts are better when done curved. After curing lift the sides up and fasten the cutout corners back to their place. Now take some foam blocks, glue them inside of the open corners, carve them, might need a bit of fairing compound, and laminate over. Laminate inside after removing the foam plugs.

    tried to attach a drawing but maybe smth wrong with the server update??
  3. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    You must keep it very light. Consider aluminum tube framing with canvas stretched over or a tall bimini top with side/front eisenglass enclosure.
    I think steel is a bad choice, too heavy if strong enough, too weak if light enough, and of course, the corrosion.
  4. DianneB
    Joined: Jan 2010
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    Location: Manitoba

    DianneB Junior Member

    Both fibreglass over ply and fabric over tube wouldn't give me the strength to support a person on the cabin roof - I need some type of framework.

    In working with the design, a frame of wood (maybe White Oak for strength) is easy to fabricate and aesthetically pleasing but requires more depth (which takes away from head-room) than steel. Aluminium, unless using a high grade, doesn't give sufficient strength/weight advantage to justify the cost although its corrosion resistance is a big plus.

    Still pondering the options ......
  5. apex1

    apex1 Guest

    Glas fabric / Epoxy over ply can give you more strength than any other feasible material, and it is by far the easiest to handle.


  6. PhotoBoatGuy
    Joined: Feb 2004
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    Location: Redmond, WA

    PhotoBoatGuy Rhino fanatic

    Just a note about the design. You note you want sliding windows on the side and the ability to have a person stand on the top.

    Be sure to consider adequate mullion strength or that guy on top will break the windows.
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