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Cargo Work

 

Container Cargo

 

 

Sea Containers were invented in the mid 1950s by Malcolm McLean, a North Carolina trucking owner who grew tired of wasting his trucking company’s time with trucks standing idle in line as ships were unloaded bit by bit by dockworkers. 

McLean developed sealed truck trailers and the concept of loading and unloading the trailer interiors only at the points of origin and destination. 

The first ship modified to accept these “containers” on deck, sailed with 58 of them from New York to Houston in April 1956. This was the start of McLean’s company, the Sea-Land Corporation. 

The Matson Line (Hawaii) put the first fully containerized ship into service in 1960. 

The International Standards Organization (ISO) first established container standards in 1961.  The ISO standard is not prescriptive and instead simply stipulates tests that the containers must pass.

Modern container ships have only one problem – when the ship arrives in port, the object is to unload the containers quickly to get them on to their final destination and to get the container ships back out to sea fully loaded heading for the next port. 

To accomplish this, container ships are equipped with steel skeletons called “cell guides”.

A special lifting fixture is used with remote actuators, which engage the corner blocks on the top of the container. 

A recent survey indicates that port crane operators can execute full crane cycles to remove and position containers at rates of between 30 and 60 boxes per hour.

 

 

 

Containers come in two basic sizes – 20 Footer and 40 Footer and are commonly known as TEU (Twenty Equivalent Units) and FEU (Forty Equivalent Units).

The external body of the container is made of corrugated sheet metal and is not capable of taking any load. The four corners have shoes and are strengthened to take in load.

The inside bottom has a wooden ceiling. There are weather-insulted vents provided to facilitate venting.

The weights marked on the containers are TARE weight and LADEN weight. TARE weight is the weight of the empty container and is usually 2200KGS for a TEU, while the LADEN weight may be anything from 20000KGS to 32000KGS (strengthened steel construction).

The container shoes fitted at the corners are hollow with 5 oval slots to facilitate the fitting of container fittings as well as for lifting the container – either by using conventional wire slings or by spreaders.

Since the containers are concentrated weights the loading of the same require special heavy dunnaging to spread the load evenly over the deck – if carried as deck cargo on conventional general cargo ships.

However the carriage of containers are primarily on container ships or on ships, which have been built to take in general cargo as well as containers to a limited extent.

Lashing of containers on purpose ships are supplied from reputed lashing makers and have been tested for the loads they are to lash. Various fittings are used and all of these are generally carried on board.

                  

Base stacker                             Twist Lock                                           Double Stacker

 

             

Corner Eye Pad                                                Side Stack Thrust                                 Bridge Fitting

      

Twist Lock                               Rod Lashing Bar                                               Spacer Stacker

A spacer stacker is used where there is a difference between adjacent containers as loaded in their heights, one being the 8ft and the other 8.5FT.

On normal ships where these fittings may not be available wire ropes are used however the number of ropes to be used would be decided by the weight of the container.

On GC ships with no provision for built in shoes only single height loads are carried.

However on container ships the hold stacks may extend to 7 high and on hatch top/ deck to 5 high.

The hold and the deck/ hatch top being strengthened.

The lashings to be done are specified in the container-lashing manual supplied to the ship from the building yard. This is not to be reduced since the stresses have been calculated and the number of lashings incorporated.

The containers are loaded onto a container ship in a specified manner. The ship is divided into BAYS or ROWS. Looking from the side the bays are marked from forward to aft.

The containers are stacked in tiers and are in general called the stacks.

This way ensures that any container can be located very easily – knowing the bay number and the row number isolates the location and the stack height give the exact position of the container.

On container ships the containers are lowered onto slots inside the holds, the holds bottom is provided with sunken shoes, twist locks/ stackers are fitted onto these and the container is lowered onto them.

Cell Guides on Deck – Open hatch concept:

Some containers are designed to carry refrigerated cargo, these special containers have their own cooling plant in built on one end of the container, and all that is required for the ship to provide is a power point for the electricity. The containers come with their own recording device and card, the ships officers has to renew the card on the expiry of the same, and is to see that the cooling plant does not stop functioning, manuals are provided whereby ships staff can do some minor repairs to the plant.

Today a variety of cargo which previously was thought could only be loaded onto a general cargo ship, is transported on container ships. An example is a tank, thus small parcels of liquid is carried on container ships.

Lashing of containers is very important since a typical container ship has a low GM(F), consequently the ship rolls quite a bit and the stresses developed by the cargo swaying is liable to break the lashings and put the containers into the sea.

            

All lashings are to be done following the ships lashing manual. In general the following is a typical lashing system, others may also be accepted if permitted by the manual.

The planning of loading of a container ship is normally undertaken ashore, but the officer in charge of the watch should keep an eye on the loading to detect errors in stowage which may occur. A particular watch should be kept for containers with dangerous goods placards to see that their stowage satisfies segregation requirements as laid down in the IMDG code.

Other things to watch for are that container marked for underdeck stowage do not end up on deck – this is serious since the container may be for second port by rotation, also the heavier containers are generally loaded underdeck to increase the GM. Thus in addition to a loss of GM the ship would also have a mess up at the disport.

Refrigerated containers should be loaded where they can be connected to the ship’s power supply and the duty officer is to ensure the same. While loading a slight slackening of watch can become a liability since the gantries load very fast and to unload or to shift is expensive and time consuming – even if the fault actually is of the port.

Sometimes containers are loaded which due to the nature of the contents have to be overstowed, in this case the container is loaded and the container is then blocked off so that there would be no chance of any pilferage – such containers may carry – currency/ coins, drugs, and mail or other high value cargo.