Insurance connecting system for a folding hull...

Discussion in 'Boat Design' started by valter.f, Mar 3, 2015.

  1. valter.f
    Joined: Jun 2013
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    Location: brazil

    valter.f Junior Member

    Hi friends,

    35ft, wood thai catamaran hull (2ft beam - canoe style).

    I just found this and think not safe. I can build in stainless steel. Do you have any idea or plan?

    [​IMG]

    Thanks,
    Valter.
     
  2. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Quarter- twenty fasteners, especially the ones in stainless steel, are not even close to adequate for a 35 foot cat. Do not use tee nuts. Those things are for cabinets, maybe beer signs, but not boats.
     
  3. valter.f
    Joined: Jun 2013
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    Location: brazil

    valter.f Junior Member

    Hi,

    May not be viable, but it is possible. Paul Fisher is a renowned designer, one of the best in my humble opinion, and indicates this technique to one of its projects with 40ft, but also find it very simple.

    40ft Dragon by Paul Fisher (three sections):

    [​IMG] [​IMG]

    Thanks,
    Valter.
     
  4. Kailani
    Joined: Apr 2013
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    Kailani Senior Member

    Can I ask what you mean when you say "Insurance" here?
     
  5. valter.f
    Joined: Jun 2013
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    Location: brazil

    valter.f Junior Member

    Hi,

    When I say "insurance", I mean a system that will unite the sessions in its entire circumference and not just side of the hull.
    Something that allows me to safely navigate in coastal waters, but a chops sea, and without the risk of breaking the hull in half.
    I need this option to make the trailerable boat.

    I thought of something like this, built with stainless steel profile, but wanted to have other options.

    folding hull1.jpg hull folding 05.jpg junção casco 6.jpg hull folding boat.jpg

    Tks.,
    Valter
     
  6. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Consider that half the 34...35 foot boat is about 17 feet long. Consider that the center of buoyancy of the front half, or the rear half of the boat is about 8 feet from the connecting joint. That makes a substantial lever when mounting a wave or receiving a wave from astern. If the joint fasteners are say 18 inches apart in the vertical direction, then the lever ratio is 8/1.5 or 5.333. Now 5.333 times 8 feet makes a tension force on the bottom most point of the joint of 42.666 times the force of the buoyancy of the half boat. Suppose half the displacement of the boat is 400 pounds. Multiply by 42.6 and you get 1700 pounds of force that the fasteners and the bulkheads must withstand. That is the general idea.

    Add to that, the dynamic forces which may be substantial if the boat is moving fast. The connections had better be very substantial unless you plan to go swimming. Any attempt to violate the laws of physics is doomed to failure. The joint has to be bulletproof.

    One can argue that WW2 Douglas DC3 airplanes used quarter inch fasteners to hold the wings in place. That would be true but there were about a gazillion of them, strategically positioned, holding each wing in its assigned place.
     
  7. valter.f
    Joined: Jun 2013
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    Location: brazil

    valter.f Junior Member


    You are right ... Even knowing that we sail in coastal waters, we were calculating this dynamic for the accidental event of 10 ft waves, and came to the same conclusion of you.

    We are still studying an alternative: It is a Polynesian style catamaran sail that would have six beams under the open deck. When only the prow out of the water, a big wave, for example,
    these beams will avoid this counterweight since the hull is fully fixed in the beams and deck, thus the force is not only about the joint, but around the hull. Besides all this, we are thinking of reducing to just
    30 ft (8 m) or divide into two or even three sessions.

    I know this is not feasible, but we need to hauling this catamaran and that's the only way. The other would be not build it.

    Having this information and know this new design of the connection, what do you think?

    (Forgive me. My english is very bad... :) )

    Thanks.

    HULL CONNECTOR 1.jpg HULL CONNECTOR 4.jpg HULL CONNECTOR 5.jpg HULL CONNECTOR 6.jpg HULL CONNECTOR 7.jpg HULL CONNECTOR 8.jpg
     
  8. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Looking for simplicity perhaps could study the place a neoprene ring with several screws (similar to that shown in the post # 1) that secure the tightness of the seal and place 3 or 4 longitudinal girders, removable, covering six frames ensuring sufficient longitudinal strength of the boat.
     

  9. valter.f
    Joined: Jun 2013
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    Location: brazil

    valter.f Junior Member

    Hi,

    The idea is good and economical, but there would be no reinforcement below the water line. Maybe something like the attached drawing, but another problem starts arise. The costs.

    In Brazil is there a quote that says: "The sauce can not be more expensive than the fish" ... But I do not see many alternatives to build a completely safe and economic connection... :confused:

    two sections connected 1.jpg

    Thanks,
     
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