Interesting sign on that Amazon box, 'Stack limit 3 high'.
My understanding from my time visiting container terminals in the UK is that the ground stack limit here is 5, although I don't know if that's a worldwide recommendation?
Why would Amazon boxes be limited to 3, or is it a 53ft-box thing, which still raises the question, why only 3?
It's the corner posts I believe, they're light weight containers as are most US domestic 53' units, therefore there is no need to construct them stronger to withstand higher loading in vessel holds or on deck for international traffic. I believe the limit is for loaded boxes as I've seen photos of MT's stacked much higher.
Ground stack in the UK is variable, usually constraints on surrounding countryside but within the port we stacked six high in the park, both loaded and unloaded and eight (8'-6" units) high in the MT's park; the restrictions here are the machines, an eight high MT handler is a bloody big and expensive piece of kit and swinging a 45' that high is an art and frankly scares the living daylights out of me. MT drivers are a different breed and a law unto themselves on the dock, they have the best welfare facilitates but then they're the only ones that can shift boxes at vast rates (think the record is just under 50 in one hour).
On the biggest vessels they typically stack 10 or 11 in the holds and that's dependent on the container height mix, ten 9'-6" or 11 8'-0" etc; it's a real ball ache when the planner gets it wrong and the hatch lid won't go on by a few inches and the errant over height is five or six deep.
Above deck is dependent on lashing bridge height, I believe they're limited to +5 above highest lashing bar using bobbins only, typically lashing bridges are physically 3 or four high and typically you can reach containers two above that to fit the bars. I have seen eleven high aft the bridge (typically all MT's back there) and lashing bars only up to four high
so some one was winging it.
I've been gone five years now so don't have access to loading/discharge plans and there's a new generation of vessels on stream so they may be more below deck; unlikely as the hull form seems set for the current moment, extra capacity coming from reorganizing the above deck layout, reducing superstructure impingement, beam and length increases.
This is a ten high stack failure from rough weather in the Bay of Biscay, note lashing bars only extended to the base of the third row from a one high bridge, they could have gone one higher but deemed it safe not to as they were empties and the risk of racking minimal. Even if they had gone to the base of the four row it would not have made a shred of difference, the failure was way up at row six.
Maersk got slapped for this, fined and forced to go back later with very expensive gear and salvage as many missing boxes they could find, at the time this was the biggest single loss of boxes in one event, there have been more recently with even higher losses I believe. One of the crew members posted up a video when they were in the rough seas, that mooring deck was completely awash and often submerged with the waves.
) is a good back up plan.
