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  1. #141
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    Quote Originally Posted by Richard Winn View Post
    if the boom collapse had not disipated the energy the ship would have sunk
    ????

    What energy needed dissipating? The cables clearly were not elastic, as they show almost no rebound.

    Force, yes, but that went to zero RFN when the hook broke. Energy? I'm not seeing it. Do you mean maybe the potential energy converting to kinetic energy once the boom went over-vertical? Not sure how that translates to sunken ship.

    Regards.

    Mike

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    There's a very good chance that hoop stress and modulus of elasticity in the nut material cause the nut to expand and unzip from the thread. Somebody probably designed or cut one pass too much in the thread causing too much slop in the thread. When loaded, the radial engagement was minimal engagement and was lost when loaded and expanded and the nut unzipped from the engaged thread. Something this massive may require a thread with a depth of over 2" and probably a four pitch or it's equivalency in metric. I've seen this happen in heavily loaded threads we use in down hole oil field equipment.

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  4. #143
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    Quote Originally Posted by Finegrain View Post
    ????

    What energy needed dissipating? The cables clearly were not elastic, as they show almost no rebound.

    Force, yes, but that went to zero RFN when the hook broke. Energy? I'm not seeing it. Do you mean maybe the potential energy converting to kinetic energy once the boom went over-vertical? Not sure how that translates to sunken ship.

    Regards.

    Mike
    cept for the shank everything worked as designed

    better to have a mangeled boom than an upside down ship

    ballast roll of the ship= boom headed up in an uncontrolled manner when load is

    released

    if you try to stop it there is your force

    they did get that part right just looks bad but it did work cause they are not upside down

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  6. #144
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    Quote Originally Posted by jmead View Post
    Excellent video Motion! But I can’t picture scaling that up ( my imagination is slipping) to even 2% of that capacity, even 1% would be an amazing innovation. A huge amount of hyd fluid keeping it level would have to move from the load side to the counterweight side in an instant when the load let go. Not the moon landing or 737 MAX of engineering problems but still.
    Daniel explained the concept. The idea is much easier than the Stewart platform in the video, but the concept is the same with respect to holding a consistent absolute position even when the ship rolls.

    it would be fairly simple to calculate the max pitch and roll velocity and acceleration of the ship. You would then need to ensure that the boom angle winches could support those same velocity and acceleration requirements. No doubt it would take some power, but you have the inertia of the boom and any payload working in your favor and this would significantly reduce power requirements.

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    Quote Originally Posted by Finegrain View Post
    ????

    What energy needed dissipating? The cables clearly were not elastic, as they show almost no rebound.

    Force, yes, but that went to zero RFN when the hook broke. Energy? I'm not seeing it. Do you mean maybe the potential energy converting to kinetic energy once the boom went over-vertical? Not sure how that translates to sunken ship.

    Regards.

    Mike

    There is a chance that if the ship had not hit the dock, it might have rolled considerably farther, potentially allowing the boom to overbalance it and cause it to capsize sideways.

    We don't know about that, the ship may be stable enough to avoid problems. But the counterflooding plus the boom overbalance might have continued the port list to where it ended up sunk lying on its port side. Hitting the dock may have prevented a rather larger problem than what exists now.

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  9. #146
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    Do you think that performing the tests, or actual lifting, should be performed only over the stern or bow? Would make ballasting much simpler.

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    Quote Originally Posted by motion guru View Post
    Daniel explained the concept. The idea is much easier than the Stewart platform in the video, but the concept is the same with respect to holding a consistent absolute position even when the ship rolls.

    it would be fairly simple to calculate the max pitch and roll velocity and acceleration of the ship. You would then need to ensure that the boom angle winches could support those same velocity and acceleration requirements. No doubt it would take some power, but you have the inertia of the boom and any payload working in your favor and this would significantly reduce power requirements.
    Its not even that complicated. Naval guns were dynamically compensated by WW1. Like you state, inertia wants to keep the barrel steady while the ship pitches and rolls, so it doesn't require much power to keep the barrel stationary.

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    A heavier base or foundation always seems to make things better mechanically.

    Ship draft could be considered the foundation.

    Would it had made much of a difference, if the ship would of had a much deeper draft?

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    Quote Originally Posted by swatkins View Post
    Do you think that performing the tests, or actual lifting, should be performed only over the stern or bow? Would make ballasting much simpler.
    I thought of that too. If over the stern the ballast weight would be much less. However the pedestal that the crane is on certainly must go all the way to the bottom of the ship.It would interfere with propulsion and the dynamic positioning. That starboard side is the only place it could get close enough to the load.

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    Should be a pic of the broken hook shank still with nut attached....I do have a Qld open crane ticket ,admittedly done 50 years ago on a crawler crane.,and hook fail is one thing I would never allow for .....but I would allow for wire rope or chain sling failure ,which is pretty much the same result...I suggest the boom was at max elevation ,and for sure its very easy to go over backwards from there ...Been done many a time....The check lines wont stop a boom going over either ,because of the small difference in centres between the boom pivots and the stays ,the stays break easily.....in fact ,normally ,the stays going tight knocks the engine clutch out of engagement ,obviously the computer equivalent nowdays.......But lightweight HT tubular booms are notorious for collapsing suddenly ,as we see here .....normally doesnt do a great deal of damage to anything else on the crane.

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    Quote Originally Posted by motion guru View Post
    Daniel explained the concept. The idea is much easier than the Stewart platform in the video, but the concept is the same with respect to holding a consistent absolute position even when the ship rolls.

    it would be fairly simple to calculate the max pitch and roll velocity and acceleration of the ship. You would then need to ensure that the boom angle winches could support those same velocity and acceleration requirements. No doubt it would take some power, but you have the inertia of the boom and any payload working in your favor and this would significantly reduce power requirements.
    The boom hoist is the largest mechanical advantage and the slowest hoist of any crane. The only way to do that would be a boom that could go live (free falling) for a very short time regaining control of it would be a challenge.
    Last edited by tdmidget; 05-11-2020 at 05:44 PM.

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    Quote Originally Posted by tdmidget View Post
    The boom hoist is the largest mechanical advantage and the slowest hoist of any crane. The only way to do that would be a boom that could go live (free falling) for a very short time regaining control ofr it would be a challenge.
    Again, the idea is that the actual boom position with respect to a world coordinate system would be static. In other words, relative to gravity, it would not move . . . no theoretical work would be done. However, the inertia of the winch drivetrain would require significant torque / power to allow the lines to maintain tension at a constant level. We have done applications like this to stabilize the position of a payload when the platform on which the actuator is moving . . . albeit, these applications were dealing with thousands of pounds, not 100’s of thousands of pounds.

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    Quote Originally Posted by motion guru View Post
    Again, the idea is that the actual boom position with respect to a world coordinate system would be static. In other words, relative to gravity, it would not move . . . no theoretical work would be done. However, the inertia of the winch drivetrain would require significant torque / power to allow the lines to maintain tension at a constant level. We have done applications like this to stabilize the position of a payload when the platform on which the actuator is moving . . . albeit, these applications were dealing with thousands of pounds, not 100’s of thousands of pounds.
    It was mentioned somewhere that the crane alone has 10x800kW drives. Sounds like lot to me but so does 5000 tons too. Some back of the envelope engineering might reveal if the drive power is enough just for lifting or also for dynamic positioning.

    Ship itself has 4 x 4,500 kW Azimuth Thrusters, 2 x 4,200 kW Retractable Thrusters and 2 x 2,500 kW Tunnel Thrusters.
    And how much power it has for ballast tank pumps compared to any normal ship?

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    Seems likely the test weight barge dropping into the water caused a tidal wave that lifted the crane hull on that side enough for the boom to go over backwards....At 1/2 weight ,the barge would be 1/2 out of the water ,so there is a massive displacement as it drops back ,doubtless deeper than its static waterline.......My conclusion ....with cranes ...shit happens ....no need for an enquiry ,just cancel any Spanish lifting gear test certificates ,as they are obviously faked.

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    Quote Originally Posted by MattiJ View Post
    It was mentioned somewhere that the crane alone has 10x800kW drives. Sounds like lot to me but so does 5000 tons too. Some back of the envelope engineering might reveal if the drive power is enough just for lifting or also for dynamic positioning.

    Ship itself has 4 x 4,500 kW Azimuth Thrusters, 2 x 4,200 kW Retractable Thrusters and 2 x 2,500 kW Tunnel Thrusters.
    And how much power it has for ballast tank pumps compared to any normal ship?
    A floating crane ship needs to hold its roll and pitch angle constant in order to assemble payload bolted connections. The crane hook needs to maintain constant height with repect to the worksite despite wave motion for the same reason.

    The deep water oil well drill rigs use the same technology. The rigs have continuously running bow thrusters to maintain position and a number of hydraulic/cable jacks supporting the drill platform to maintain height with respect to the sea floor. The height control system uses accelerometers to measure displacement of the floating rig and compensates by moving the drill platform jacks. The bandwidth of the control system is slow. Perhaps one cycle/second to follow the wave motion.

    The hoist ship can compensate for wave motion by raising and lowering the hoist block. The ship pitch and roll angle control would need a faster system than water ballast. That could be a pair of large weights mounted on rails or a pair of large gimbled flywheels. The flywheel approach (control moment gyros) was used in the 1930's on a few passenger liners to reduce ship pitch and roll. The system was quickly replaced by less expensive adjustable fins external to the hull controlled by angle sensing gyros.

    The rolling weight method is used on tall office buildings to reduce tower sway during high winds. One of the upper floors is reserved for the sway control.

    A set of two fast response reversable vertical bow thrusters would also do the job. The length of the ship and the aft position of the hoist would provide a large moment arm. The earlier post appears to be describing this last method.

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    That sounds like a very interesting thought. And it would not require the absorption of a large amount of energy. In fact, if the boom is kept at the same angle, very little energy would be required. But it would allow the ship to roll more and that may be a different problem. But perhaps it could be possible to lower the crane a little slower and counteract the roll of the ship. And then take up the slack as the ship rolls back the other way, but again not quite all of it, again to dampen the roll. With the proper control of the crane's boom, the roll of the ship could be dampened while the crane is protected from going over vertical. Software!

    This sounds brilliant and should be considered.



    Quote Originally Posted by DanielG View Post
    I don't think he's suggesting anything that complicated. If you look at the video of the failure, the initial break doesn't affect the crane that much. The ship however, starts to list to port, dragging the crane over center. If, as soon as the boom-horizon angle started increasing due to the list, the winches started lowering the boom. As long as the winches can lower the boom-deck angle as fast as the deck-horizon angle changes due to the list, the boom-horizon angle would stay the same and the boom wouldn't topple over backwards.

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    Quote Originally Posted by digger doug View Post
    Forging....probably about 3 places left in the world that can handle it.

    So maybe instead, the shop just poured an ingot, oxy lance everything away that don't look like a hook, heat and beat with 20 lb sledges on the surface for the "forged look".
    This the pix I was looking for:
    Attached Thumbnails Attached Thumbnails lanceandtwistcrankshaft-1.jpg  

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    I don’t know why the hook failed; I am thinking a crack in the stem caused the hook failure. The release of energy caused the boom to whip which should have been absorbed in the length of the boom, But the boom striking the gantry with such impact that all the force was centered at that one point so causing the boom to fail. So, sharing the blame to the hook design and/or manufacturer error, and to the crane design with not enough clearance angle to the gantry.

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    That brings up another interesting point. The contact with the A frame was at a single point (OK, horizontal line). All the stress was concentrated at that single point. There was no question but that it would bend at that point.

    Perhaps, just perhaps, some additional, almost vertical members could be added, attached at the top of the A frame and extending both above and below that point. They would be designed to flex more or less like a bow (al a Robin Hood fame) with the center of that flexing to be at the attachment point to the A frame. If the boom of the crane hits those flexing members they would take up the shock first at the center point and then, as they flex, at points higher and lower along those members. The impact would be distributed along a significant section of the boom instead of just at a single point. And it would also be distributed over a short, but significant time span. That could provide the needed action to prevent the boom from bending or from even being permanently damaged. Everything would stay within it's own elastic limits.

    I like this even better than the computer control of the boom's position after an accident that was discussed a few posts above. It just sits there awaiting an accident: no computer control or even power is needed. Or both could be combined to maximize the control of the situation.

    In short, it would seem to me that there are ways to control this situation, even after such a catastrophic failure. And they would be far less expensive than replacing the entire crane or major parts of it.



    Quote Originally Posted by michiganbuck View Post
    I don’t know why the hook failed; I am thinking a crack in the stem caused the hook failure. The release of energy caused the boom to whip which should have been absorbed in the length of the boom, But the boom striking the gantry with such impact that all the force was centered at that one point so causing the boom to fail. So, sharing the blame to the hook design and/or manufacturer error, and to the crane design with not enough clearance angle to the gantry.

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    In fact ,the boom didnt whip at all,as the hull heeled over ,the boom passed tipping point ,and came down against the frame .....the moment a lightweight tubular boom touches the tubes crush ,strength is lost ,and we see the result .....Anyone has ever worked a crane with a lightweight tubular boom is very aware of what happens if the boom hits any object.......Many crawler cranes came with an alternative industrial boom made of multiple angles a nd plates ,and I ve seen one of these knock the corner off a shed ...from the operators seat.

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