Help designing simple jib crane

Discussion in 'Boat Design' started by DogCavalry, May 8, 2021.

  1. Tiny Turnip
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    Tiny Turnip Senior Member

    I was just wondering the same minus the central mast. Quad swings between the legs of the A frame as it comes past vertical and can be lowered into the cockpit.
     
  2. DogCavalry
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    DogCavalry I aim to misbehave.

    Good for bow loading. I guess that's okay. Can always approach square instead of coming alongside a hypothetical dock. But then the gantry is easier and stronger.
     
  3. fallguy
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    fallguy Senior Member

    Some wiser apple needs to tell John what happens to draft with a 350 kg load on the front of his boat. My 16' skiff wouldn't make a shallow beach with 60kg about 3' from the bow
     
  4. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    The disadvantage of a gantry is that you would only be able to load / discharge cargo over the bow - in similar fashion to a garbage skip truck?
    You would not be able to load anything over the side.

    The ATV would have to be at 90 degrees though to the skip shown in the photo below.
    And I think that while you could hoist the gantry up (to bring the ATV on board) using a block and tackle attached to the wheelhouse roof (perhaps), once the gantry gets past vertical it will want to 'fall down', and you won't have an awful lot of leverage to control it if you have (eg) a block and tackle (or 2) attached to the bow to control the rate of descent.


    Skip truck.jpg
     
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  5. BlueBell
    Joined: May 2017
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    BlueBell "Whatever..."

    Other than bricks, John's also talked about loading 55-gallon drums weighing in around 460 pounds (210 kg).
    If we rule out the ATV requirement of 800 pounds and ample vertical capacity, the jib crane seems more doable,
    but in a smaller size.
     
  6. DogCavalry
    Joined: Sep 2019
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    DogCavalry I aim to misbehave.

    This forum is the crucible that burns vague notions into reality.

    Or something like that, but poetic.

    A gantry. Cheap and easy to build, more than strong enough. Quite limited compared to a proper derrick, but much safer.

    So some back story: my first career was as a combat engineer. I have extensive experience in field machinery as we called it. Gin poles, sheer legs, aerial ropeways. Bridges built from logs and boulders. I have no doubt I can control a hinged gantry safely.
     
  7. fallguy
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    fallguy Senior Member

    I also have no doubt you can build a barge for some of your plans.
     
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  8. DogCavalry
    Joined: Sep 2019
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    DogCavalry I aim to misbehave.

    I am sure I will.

    Next year. This boat is already cleaning me out.
     
  9. fallguy
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    fallguy Senior Member

    Keep your eyes open; you may see an old derelict pontoon somewhere..
     
  10. DogCavalry
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    DogCavalry I aim to misbehave.

    Draft increases from 6" to 13" at the bow. Goes from 5" to 4¾ at the transom.
     
  11. DogCavalry
    Joined: Sep 2019
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    DogCavalry I aim to misbehave.

    Just looked up my other big ticket delivery: Sub Zero 48" built in fridge. 630 pounds, $16000. That's a lot of money and weight for a box to keep your root beer cold.
     
  12. fallguy
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    fallguy Senior Member

    Well, that is also a dose of reality I'd say. Shore landing with lots of forward load will be hard to do..
     
  13. DogCavalry
    Joined: Sep 2019
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    DogCavalry I aim to misbehave.

    Yes. A quad is fine in 13" of water. A $16000 beer fridge is not.
     
  14. DogCavalry
    Joined: Sep 2019
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    DogCavalry I aim to misbehave.

    Ad Hoc has, as is his habit, distilled the question for me. My SOR: get an 800# quad into and out of the cockpit, safely and under control. For that a hinged gantry is adequate. It requires no special parts or materials, or modifications of the boat. It has less flexibility than a HIAB or even the simple jib crane I first thought about, but it meets the SOR. Sketches to follow.
     

  15. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    A sketch, with dims or drawn to scale, of the plan and profile of the boat, the part where you wish to place the quad.
    The sketch showing where bulwarks/structure etc is located.

    Then we can look at the limitations, if any, and see where/how best to arrange safe retrieval and launching of said quad.

    The key thing in everything related to structural design is - load paths.

    I know it is 'silly' to ask, but I will anyway - as engineers we need black and white. Do you have a set of hydrostatics for the boat?
     
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