Quik kids cat

Discussion in 'Boat Design' started by boatindad, Feb 13, 2014.

  1. boatindad
    Joined: Feb 2014
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    boatindad Junior Member

    I appreciate the encouragement. We are working on several different options for steering and power. I have a 12v black and decker drill with no batterys, an apc10x7 model airplane prop I'm going to try a 1/2inch pvc heat bent with a drain snake for a shaft. I also have a 12m cabrina kite if the video works you can see me blow a 50 dollar bladder. I think I will take your advice petros and make a small standard sail to play and learn with. For steering I think 1 large central rudder tiller style to start but i would like to experiment with a four corner rudder/tab "thingy" like peter lynn's kitecat. Farther into the future i would like to try four wing sails . Again thank you gentlemen
     
  2. boatindad
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    boatindad Junior Member

    Ok I want a little input. I want to know if a 2x6x8 split length wise and screwed and glued to make a right-angle beam(L shaped) would be strong enough for akas the span is about 8ft but only 6ft unsupported. I have read about lighter box beams, tiki(Wharram) style Ish beams and solid. Personally I only have knowledge about the span based on home carpentry: 12-24in centers vs span length. This is a learning/building platform so simple function gradually moving towards greater complexity is the goal. The budget is also a constant constraint 20-40 US per week for upgrades. I have netting for the trampoline, I also wonder if it can be attached on only 2 perpendicular beams.
     
  3. boatindad
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    boatindad Junior Member

    I just found out how to "like" the posts I've been wanting to but didn't understand so likes to ya.
     
  4. messabout
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    messabout Senior Member

    If you rip a 2 x 6 down the middle you will have about 2.68" of aka depth when accounting for saw kerf. I think that will be too flimsy. Think of a box beam a little deeper than the split two by.

    SWAG.... top and bottom 3/4 x 3, 3/8 ply sides 4 inches deep. That'll be much stiffer and weigh about the same as the 2 x 6. Taper the ends if you want to be fancy.
     
  5. boatindad
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    boatindad Junior Member

    I mean to take the two halves of the 2x6 and rejoin them in an L shape with glue and screws. I'm not sure if that was clear.
    It would be 4.43 inches on the vertical using your calculations.
     
  6. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    An L is vastly inferior to a box in terms of bending strength.

    Additionally, if the boat ever is pushed very hard by a sail, there is a significant amount of torsion in the beams. This is what keeps the bows from twisting out of plane of each other (an L has very little torsion strength). Take your plank and make the best box beam you can, gluing the joints with epoxy to get the max strength from the wood. If you have the wood, make 45 degree reinforcement in the corners when you glue. If you find the beam is not strong enough or more flexible than you like, glue solid "planks" on the outside. 1/4 thick will add a great deal of strength. If you have it, glass the outside of the beam with 6 oz (or whatever you have).

    Don't use an L.

    I one time built a catamaran row boat with box beams (6' wide, 4" on the side of the box). The original beams weighed 9# each.
    Second try I actually tested what was "good enough". The beam was 1/8" ply on the sides and 1/2" cedar on the top and bottom - a 2" square crossection. My wife and I stood on the beam at the center as a test - good enough since only one person could ever be on the boat. Then I glassed it. 2# each.
    This sizing wouldn't work for you because there were no other loads on the row boat, but the box beam is very strong and relatively easy to build.
    FYI, put solid blocking where ever you will be attaching bolts.

    Also, if you are going to glue with epoxy, don't bother with screws except to hold the wood in place while the glue cures. Under load if the glue breaks but the screws hold then you just wasted the glue.

    Actually if you are near Ft. Worth, Tx I'll give you the old beams.
     
  7. boatindad
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    boatindad Junior Member

    Ok so box beams it is. I just learned(taught myself) how to draw on paint with a grid background. a small step but it makes me happy. Thanks for the input. What is the best corner joint for box beams ? I have a router.
    Thanks for the beam offer but I"m in ohio.
     
  8. upchurchmr
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    upchurchmr Senior Member

    The only real thing needed in the joint is more surface area.
    You can get a little bit with a routed joint but adding a corner block gives more.
    The fiberglass adds more strength to the joints
    When I said glue fillet I meant in place of the blocks

    [​IMG]
     
  9. boatindad
    Joined: Feb 2014
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    boatindad Junior Member

    electric outboard

    I threw together a motor today its a weedeater shaft 11x7 air prop and a 12v black and decker cordless drill I took it to the river and could only go in circles. My kayak doesn't track well it had some power, it would pull harder than i could paddle 20140424_140331.jpg

    20140424_140343.jpg

    20140424_140356.jpg
     
  10. Navygate

    Navygate Previous Member

    How cool is that!
    What torque/RPM setting worked best?
    Have you looked at the Pedal Powered Boats thread (sorry, don't know how to link).
    There is fascinating info there on how to run a 1/4" spring steel flex shaft unattached (free floating) and it tracks fine!
    Self centring, self guided.
    Only attached at the drill end.
    Ridiculously simple and effective.
    Check it out.
    :)
     
  11. Jim Caldwell
    Joined: Aug 2013
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    Jim Caldwell Senior Member

    You need less diameter and more blade area, try 2- 8x6 pinned together to make a 4 blade prop.
     
  12. Navygate

    Navygate Previous Member

    What do you base that on Jim?
     
  13. messabout
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    messabout Senior Member

    I suspect that Jeremy Harris is the resident authority on props powered by electric drill motors. He has done a mess of competent R&D for the benefit of his race boats.
     
  14. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    maybe its that bend in the shaft :p

    PS - a good hint - if you stick a prop on a long but flexible stainless steel shaft, it doesn't need a lot of support to stay centred while in operation.

    It will tend to self centre and stay quite rigid under power even if it sticks out a long way from the closest support block.
     

  15. Jim Caldwell
    Joined: Aug 2013
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    Jim Caldwell Senior Member

    We run into this with our Fast Electric race boats. Too much diameter and you get "prop steering" but if you decrease the diameter you lose the blade area that gives you thrust. I haven't found a way around this in the 25 years I have been racing all over the USA and neither has any other racer and we have all tried. I have over 100 props trying.

    My suggestion is a cheap way to maybe get in the ball park.
    It will also lesson the Tq. on that weak bend in the shaft.

    Do you mean Chris Harris?? If so, yes we have raced together for decades and progressed from 1 hp drill motors to 12 hp electric motors in that time.
     
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