Strongback design for a barrel back kayak

Discussion in 'Wooden Boat Building and Restoration' started by cthippo, Mar 28, 2021.

  1. cthippo
    Joined: Sep 2010
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    cthippo Senior Member

    I'm starting to think about my next project and I think I want to build a barrel backed kayak using the cedar strip construction method. I've built cedar strip boats before, but in the barrel back design the sides flow from a concave shape at the bow to a convex shape at the stern. Making this shape with cedar strip isn't terribly difficult, but delineating the seam between the deck and hull will be a bit tricky. I think I will have to run the seam on a diagonal from the bottom of the curve at the stern up to the top of the gunwale where the side is vertical. Anyone else on here had to do a weird mating on a strongback like this before?

    https://images.app.goo.gl/u25N9WRiAycdTW1VA
    https://images.app.goo.gl/jt6h99fBN4xCbwfUA
    https://www.woodyboater.com/wp-content/uploads/2015/11/Chris-Craft-barrel-Back-low2.jpg
     
  2. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    The challenge is extremely similar to determining where to split a mould for hull with tumblehome.The geometry will only permit one location at each longitudinal point and that is where the beam is greatest.You can determine this from your lofting or CAD model and create a curve that passes through the points in the sheer view.Don't expect it to be a simple planar shape,although you might get lucky.I would make a big effort to let a batten into the strongback at this location so that a trim router could cut to the correct shape before removing the hull or deck from their respective formers.The only realistic way to proceed is to built the upper and lower parts of the boat the same way and then join them.Again,not hugely difficult but you still have the nightmare job of glass sheathing them.i would go quite a long way to never have to glass sheathe any project ever again.Which is why I would tend to do this one from cold moulded veneer and no glass.Much the same process and much the same joint matching challenge.
     
  3. upchurchmr
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    upchurchmr Senior Member

    Make the mold split at the top and the bottom.
    This eliminates all the above discussion.
    Saw it from the man who built Meade Gougeon's Elder Care sailing kayak.
    I think it would eliminate a lot of problems in a boat which doesn't have a distinct deck to hull break line.
     
  4. wet feet
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    wet feet Senior Member

    Same process, rotated 90 degrees.Flat plane for the join, equally awkward to get inside.
     
  5. cthippo
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    cthippo Senior Member


    That......would work. That is really clever and would work.

    I think I might make a quarter scale strongback to try some of this out before i go full scale on it.
     
  6. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    As upchurchmr said, and strip in female molds. That way you glass the inside first, glue in the bulkheads and then join the halfs. Fairing and glassing the outside is done with the boat in one piece. If needed you can use some temporary XPS bulkheads to maintain shape during fairing, they are simple to remove afterwards.
     
  7. upchurchmr
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    upchurchmr Senior Member

    You might also check on the Microbootlegger kayak.
    It was inspired by a similar power boat and has some of the same elements of shape.
    But it is done with a traditional hull/ deck construction.
    In this case the fore deck is more "barrel" shaped than the aft deck.
    A bit of a pain, since it is harder to get the hull to deck joint to match after you glass each separately.
    But I made one and it came out good.
    microBootlegger | Guillemot Kayaks https://www.guillemot-kayaks.com/catalog/strip-built/recreational-kayak-canoes-solo-tandem/microbootlegger
    Some more information like section cuts: micro-Bootlegger: Elegant Strip-Built Tandem Kayak from Nick Schade https://www.clcboats.com/modules/catalog/boat.php?category_qn=kayak-kits&subcat_qn=recreational-kayaks&code=micro-bootlegger-strip-planked-tandem-kayak-kit
     
  8. cthippo
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    cthippo Senior Member

    There is a lot to like in the MicroBL design, especially in the hull form.
     
  9. upchurchmr
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    upchurchmr Senior Member

    If you think about one, it is a little short for a double for normal sized people, but especially anyone tall.
    The displacement claimed is 450# so it is definitely bigger than a single.

    Pity you are so far away, mine is for sale.
    Never been in the water.
    It was built for my daughter and her ex. She won't go by herself at all.
    Its a good 3-4' boat. Looks great at that distance, LOL!
    It won't sell for much here in Texas.
     
  10. cthippo
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    cthippo Senior Member

    I like some of the design elements, but I wouldn't build one. This is a first boat for my primary partner and so it will be a solo boat and a fair bit shorter. Shooting for 12 feet and 26" beam with a high block coefficient.
     

  11. upchurchmr
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    upchurchmr Senior Member

    Did you see the microbootlegger solo?
    Might be about those numbers.
    Actually its 14' x 26".
    I don't know what qualifies as "high" block number, but it is quoted as 0.45.

    The illustrations Shade uses never accurately portray the shape, in my opinion.
    If you can find a picture that would be better.
     
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