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How Do Container Ships Work?

A container is loaded and then brought to the port by a trucking company. Bringing containers to the port or from the port is called "drayage".

how do container ships work flat rack container

The most common containers are 20 foot dry and 40 foot dry containers example shown on left above. There are also refer (refrigerated), high cube, 45 foot, flat racks, open top, open side, liquid and many other specialty containers available for every conceivable cargo load.

how do container ships work: container stacks

The container is kept at the port in the container stacks until the designated ship arrives.

Once the designated ship has arrived, the container is brought to the ships side by a special chassis and cab called a bomb cart (photo above). At most ports container movement is computer controlled. It is necessary to place each container in its correct position on the ship based on important factors such as container weight and the port designated for off loading.

how do container ships work gantry crane

The container gantry crane attaches to the container and lifts it off the truck (left photo above). The truck drives out from under the container. The container is held at the truck flat bed height for attachment of the securing fittings (right photo above).

Depending on the ship configuration and if the container will be secured above decks or below the hatch covers the Stevedores (1 on each end of the container) take the proper container fitting out of the flat rack twistlock bins and attach them to the container corners. Flat rack bins can be seen on the deck in the picture above (left photo).

For above deck stowage:

No fitting needed (For the first layer above deck some ships keep the twistlock permanently in the container foundation)

No fitting needed (if cell guides are used above deck)

Fully Automatic Twistlocks (automatic lock and unlock)

Semi Automatic Twistlocks (automatic lock and manual unlock)

Midlocks (if two 20 foot containers are stowed in a 40 foot slot then midlocks are used where the containers meet)

For below deck stowage:

No fitting needed (if cell guides are used below deck)

Hanging Stackers (hang from the upper container in the stack but don't lock on container below)

how do container ships work load container

After the Stevedores have placed the fittings in the container corners (if needed) the crane moves the container to the correct position on the ship. The container is lowered and released. If an automatic or semi automatic twistlock is used in the container corners the weight of the container locks the fittings at the container corners onto the container below.

The above photo shows a container ship that uses no hatch covers. The cell guides run from the tank tops at the bottom of the ship to the maximum container height. On a ship like this the containers can be loaded without fittings directly into the cell guides. Cell guides are metal structures that keep the containers in place without any other equipment being needed such as twistlocks, lashing bars or turnbuckles thus making loading and unloading faster and less costly.

The disadvantage of a ship such as this is that cell guides inhibit the ships flexibility in that it can not take a variety of container sizes and in addition the number of overall containers is reduced due to the stack weights (the number of containers in a stack are limited by overall weight).

Below deck containers (below the hatch covers) are held in place side to side but are not locked to the above or below containers. Below deck containers need no additional securing. The hatch covers are put in place and then containers can be loaded on top of the hatch cover. Above picture shows a container ship without containers stowed above deck. The hatch covers are removed for access to spaces below deck.

For above hatch cover container stowage after the containers are set in place and the twistlocks are locked (automatically for semi automatic and fully automatic twistlocks) lashing bars and turnbuckles must be attached and tightened. Above picture shows common pattern of turnbuckle and lashing bars used on containerships. There is a cross pattern for every box from deck to bottom of 2nd tier along the complete row. There is an additional pattern of lashing from the bottom of the 3rd tier to the deck on the end container stack and possibly the 2nd to end container stack. In some cases vertical lashing bars are used on the outer stacks only. Vertical lashing bars attach to the bottom of the third container height and help to increase stack weights.

container securing equipment How Do Container Ships Work?

The picture above shows container lashing bars and turnbuckles awaiting container loading. On the right you can see container foundations (square boxes) ready to receive the 1st layer of containers in the stack.

Once the ship is loaded and the container lashing secured by the Stevedore team the ship can depart port.

The process is reversed for unloading.

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