Prisma Preform Stingers for Bertram 20

Discussion in 'Boat Design' started by AlexSmith, May 22, 2019.

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  1. AlexSmith
    Joined: May 2019
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    Location: Costa Mesa, CA

    AlexSmith New Member

    F1B103ED-FEEA-4B4C-9F68-D290E0DBBBA1.jpeg Has anyone had experience with using Prisma stringers? The stringers on my Bertram 20 were rotted and I’m looking to use a composite stringer but can’t figure out how to make the prisma stingers work with the 26 degree deadrise of the Bertram 20. Below are some pics of the boat in its current state. 6EE9DA62-B6B9-4ABD-A534-4B3BF53CF7B7.jpeg B78B52EF-936E-4271-A780-E7BE7E0419A7.jpeg
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I would be inclined to turn the bottom into a sandwich, the existing hull becomes the outer skin, you epoxy in a patchwork of thick, high density PVC foam squares, then glass up an inner skin. All you need, a few bulkheads, you can be stringerless.
     
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  3. bajansailor
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    bajansailor Marine Surveyor

    I had to google Prisma stringers - and I see that they are supplied by Jamestown Distributors

    They mention in the link that 'These stringers feature a built-in deadrise converter ' - but is 26 degrees a bit too much perhaps?

    Alex, there is also this thread in the Projects Forum about restoring another 20' Bertram.
    1968 Bertram 20' Moppie - definitely a project https://www.boatdesign.net/threads/1968-bertram-20-moppie-definitely-a-project.62328/

    Edit - Mr E. offers an excellent suggestion above re re-building the hull bottom as a sandwich, rather than installing a new grid of longitudinal and transverse frames.
     
    Last edited: May 24, 2019
  4. mudsailor
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    mudsailor Junior Member

    Why not call up the guys at Prisma - they love a good project - as far as Mr Ed 's idea - don't do it, lots of extra weight for no reason......why not just rebuild the same way it was, use epoxy and plywood and it should last 50 years easily
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Nope, the inner skin needs not to be much weight at all, just a fraction of the outer, and with high quality reinforcement, and polyester resin.
     
  6. mudsailor
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    mudsailor Junior Member

    A single skin hull is likely 2 or 3 times as thick as the outer skin of a true sandwich hull.......so you add the foam weight and the inner skin-lots of weight. In addition it is a ridiculous amount of work.....just rebuild what was there and get out and enjoy a classic
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    The foam weighs SFA, and your inner skin needs not be thick at all, just use decent glass for tensile strength, impact damage is no issue hidden under there. Nothing like a cored boat to reduce noise and vibration.
     

  8. AlexSmith
    Joined: May 2019
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    AlexSmith New Member

    bajansailor and Mr. Efficiency,

    Thanks for your input. I'm leaning towards using Prisma's preform panels for the stringers and wings. I found someone else who did a Bertram 20 this way and it turned out really nice. Below is what they look like in the Bertram 20.

    [​IMG]
     
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