Ship hoist concept: Egglephantwalk2024

Discussion in 'Boat Design' started by dreamingbarrierreef, Oct 23, 2020.

  1. dreamingbarrierreef
    Joined: Oct 2018
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    Location: Colorado

    dreamingbarrierreef dreamingbarreef

    Just an wild idea I want to jot down before it's gone. I thought this should be efficient with the strength/weight. Though maybe challenging to build.

    The hoist rails are cable-stayed, and accommodates up to 16m beam. And with 6m extended bow direction & stern direction for hoisting lighter sailboats that need to clear total draft (air & water) over 20m.

    Welcome your comments.

    Attached Files:

    Last edited: Oct 24, 2020
  2. bajansailor
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    bajansailor Marine Surveyor

    It looks very complicated.
    What are (in your opinion) the perceived advantages over a 'conventional' Travel Lift?
  3. dreamingbarrierreef
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    dreamingbarrierreef dreamingbarreef

    Other than the strength/weight, also thought directional stability should be better. Conventional boxy types usually weaker on least one lateral direction. The curves and the interconnected supports probably also absorb vibrations/oscillation better.
  4. Squidly-Diddly
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    Squidly-Diddly Senior Member

    While Geodetic airframe - Wikipedia has some advantages such as holding together after sections have been damaged, and omni-directional strength, thats not normally important for ship-crane, since gravity only points down. For ship crane you only need max strength at certain points, unless you plan on operating in sever weather or hoisting ships that might be unstable or shifting weights.
  5. Barry
    Joined: Mar 2002
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    Barry Senior Member

    As an overview
    You have thin members supposedly to reduce weight. Which when designed, I would be skeptical. You have 8 points of support, the wheels. Leading me to think that you are of the idea that the conventional 4 would not be adequate.
    The inherent problem is that you appear to be making the assumption that each of the wheels will be carrying an equal load. (the variance being the strap loading due to the boat balance but assume that the boat
    was lifted equally) But as your 4 wheels per side track up the concrete, there will be small changes in flatness, causing one wheel to pick up the load of the wheel that hits a dip. And perhaps exceeding the design load. In fact if you allow for this type of flatness or even tire air pressure difference you would need to ensure that each vertical support would have to carry the entire weight with the appropriate factor of safety.
    Cost??? You will have to have 8 controllable turning wheels. If not, specific wheels, depending on the tightness of the turn will be required to carry more load. Possibly exceeding the strength of the spindly legs.
    It is attractive though.
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Just add a cross/bracing member then!
    Tiny Turnip likes this.
  7. Tiny Turnip
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    Tiny Turnip Senior Member

    looking at the cross section, arches (including catenary arches) are good at supporting continous loads that are fairly uniform across their span, and not so good at supporting point loads. The thinner the arch member, the worse it gets at point loads. Compare how hard it is to crush an egg longways in the palm of your hand with how easy it is to stick a pin through the shell. The point load can also push the arch inwards locally, and cause it to bulge outwards at other points. The cables suspending the rails impose point loads on the arches. An arch also needs restraint (ties or abutments) at the base, to resist the outwards thrust, unless the arch is thick and strong enough to provide that restraint. The curving inwards at the bottom of the arches also weakens them by making a natural point of inflection where the loads will cause the arch to buckle.
    bajansailor likes this.

  8. dreamingbarrierreef
    Joined: Oct 2018
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    dreamingbarrierreef dreamingbarreef

    Hats off & many thanks to all your thoughtful reviews and comments.

    I think the quick-sketched wireframe is probably giving some wrong impression about the structure appear to have thin members.. Actually, the idea was to use tube frames similar to the pictured canopy structures. These things have beaten typhoons, probably at least a couple dozen times already (with the canopy attached).. Those tubes are about 30cm diameter. But with technology today, I reckon 60cm or more is not too much stretch anymore. The joints are wielded with these canopies. The Egglephantwalk is envisioned to use tube clamps, loads at the cross points can be further spread out (similar with corner stiffeners with the box type corners). The (checkered) hoist frame rails can probably just use I-beams.

    Box type design can be simple and can work, no problem about that. As simple as 10 beams, albeit gotta be heavily built, plus some heavy stiffeners will do. But they gotta be heavy. And heavy is not necessarily cheaper today. Boxy type ship hoist need to have that "tunnel" open, so the bottom part can't be connected. There is definitely no problem for the perfectly straight vertical columns for, maybe practically infinite load (if straight down), but, they're not all located at cg, so forces can't be perfect straight down regardless. Have some wind to push broadside the ship, and things can become touchy very quickly with box types, if it starts to swing... All the stress hang on those corners, and all counting on the stiffeners.. To reduce some weight, or start to add more cross members and distribute stresses more evenly, design can still get complicated; and lot more ugly too. Most coastline areas are hardly ever to have a windless day. If happens, implication could be the earth is already dead. So technology has advanced a long way, why not try some new ideas..

    So with tube-clamp type joints, the point loads can be spread to longer length along the arches, and the arch type can spread overall stress and loads quite evenly (rather than focused to just the few corners) across the entire length. However, the type of design could flex more, if design load is made too close to max real loads. But guesstimate is it's probably going to be stiffer than box type if with equal weight. And the cables could be fairly good enough dampeners. And with the interconnected omni-directional support structure, uneven loads should be not much trouble. But Barry brings up a good point with the 8 wheels, or the 4 wheels on each side, the middle wheels could become like a pivot point as on a seesaw, if a outer/side wheel hits a dip. There could be a few options for remedy; perhaps including Horstmann type suspension; but this kindda thing is not likely to get budget of Yamato, or even if as hoist of Yamato. So other options may be,
    1. Just make sure the base support rails and the frame are strong & stiff enough, even in case one of the outer wheel gets suspended in air, the load can be handled by an adjacent inner wheel. The long side of the rail is still likely to be heavier, so, the shorter side is still more likely to be the load to be compensated for.
    2. Inner wheels get suspensions. So outer wheels are allowed to dip, and loads will be more evenly distributed.
    3. More exotic, the base rail is joint by four linked & pivoting (at bottom of the big circles) sections, with dampers, and allowed to bend. But this is probably just going to create more issues, and cost. So, probably not a good idea anyway.
    Choice of the remedy probably depends how rough the surface the hoist have to roll through. But the type of frame should be quite stable for reasonable amount of pitch & rolls; and there is some room for flex & twist with the type of frame. Reason for 8 wheels (or actually 8 wheel pairs) with this, is so there is ground directly under all the vertical beams. Each wheel is driven with its own motor, so each the wheel pair can counter-rotate in opposite directions, and the wheel hub can basically rotate on the spot. Controlling the 8 wheel pairs should be not much issue at all with modern computing power. Draw a line of path and the rig can be made to roll the path precisely, with ML (I like to be more honest to not use AI everywhere), and any changed conditions or variations can be handled quite well. The rig should be able to walk by itself with technologies of the day.

    For the cost, probably mainly the 6 arches and the top linking loop; and the wheel modules, suspensions (maybe), motors & generators, control system; cables, dampeners, and more straight tubes and I-beams. Arch tubes are not as expensive or exotic as yesteryears anymore. So maybe it's not going to be so bad at all...

    Attached Files:

    Last edited: Oct 31, 2020
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