TT Talk - Cargo carriage ... or a fairground ride?
- Date: 01/04/2004
- Source: TT Talk 45
When you have finished reading this stand up at your desk. Now imagine that within ten seconds you are moved to a position two storeys above you and 11 metres along the floor. And then, with equal suddenness, you are back at your desk, only to be immediately transported back again up two floors and 11 metres along ... and so on and on, three times a minute, one hundred and eighty times an hour, for days at a time... Within a few minutes of this treatment you would be begging for this torture to stop. Yet this is not some white-knuckle fairground ride, but what cargo experiences day in, day out in containers on board ship.
If they think about it at all, it is a common misconception among shippers that when "their" container gets on board ship, it will end up warm and snug, deep down in the bowels of the vessel, protected from all that nasty ocean weather outside. Anyway, that container that has arrived at the factory or warehouse for loading is a good solid thing, made out of steel. Loaded on a nice, reassuring-looking lorry. Surely nothing can go wrong? Dream on...!
Roughly half the containers on any modern container ship will be carried "on deck", up to six tiers high. As any sailor knows, the higher you go above the waterline, the greater the amount of roll. On a Panamax ship, rolling uniformly 15 degrees to port and starboard, with containers stowed thirteen across, the boxes in the uppermost tiers of the outer stacks will travel through a distance of about 11 metres vertically and horizontally. The distance travelled is actually a little longer: a complete roll cycle involves a total distance of about 28 metres. With two changes of direction this movement takes place in about 15 to 20 seconds. At the same time, of course, the container itself turns through 30 degrees and is also subject to the effects of pitch (longitudinal movement) and heave (up-and-down). With this in mind, it is indeed a miracle that most cargo reaches its destination intact. But, as the Club's claims records testify, there are still people who believe that their cargo will be safe with only a minimum of packing and no blocking, bracing or other securing within the container. Manufacturers are not the only ones at fault: many incidents involve containers inexpertly stuffed by "professional" warehouses and transit shed operators.
The forces raised in the continuous process of rolling in the ocean environment have to be resisted by the packing of the goods, together with the tightness and securing of the stow inside the container. Experience dictates that if you leave room for movement inside a container, then movement will occur. Slowly and steadily packings will crush and degrade. Do not underestimate the power of the sea