When it comes to transporting goods, containers are a vital part of the process. But just how secure are they while in transit on ships at sea?
On the open sea, ships face harsh conditions and are subject to extreme forces. If containers are not secured properly, rough weather can quickly become a recipe for a disaster. So how are containers secured on ships for ocean voyages?
The containers are secured to each other in a stack and to the deck by twist locks or stacking cones, and each stack is secured additionally to the deck by lashing bars, which are anchored to the deck and container and tensioned by the use of turnbuckles.
Container Lashing is the process of securing the containers to minimize the possibility of them shifting while being transported on a ship. Lashing becomes extremely essential, especially when the containers are loaded on deck where the external forces are constantly encountered because of the motion of the ship in various directions.
Failing to secure containers correctly is one of the most common causes of container collapse. In this article, we shall look at the process of securing containers, which parties are involved, and the equipment used in securing containers.
How Are Containers Secured For Sea Transport?
The size of containerships has been increasing over the years, and this trend is expected to continue in the future. The largest containerships can carry up to 20,000 TEUs (Twenty-Foot Equivalent Units). However, large containerships are susceptible to strong rolling motion in heavy seas, which can place an excessive strain on the cargo securing systems.
This problem was highlighted in 2020 when heavy seas caused over 1800 containers on the MV ONE OPUS operated by Ocean Network Express to be lost or dislodged from its lashings. The incident was one of the increasing incidents that highlight the need for better cargo securing systems on large containerships.
In order to transport containers safely on the deck of a container vessel, they must be firmly attached to the ship. This is done by the use of twistlocks, which are inserted into slots in the container’s corner castings.
The twistlock’s revolving lug engages the slot holes in these corner castings and locks the containers together. In addition, lashing rods link the bottom two or three layers of the stacked containers to the deck of the ship.
Stowing stacks of containers on deck in such a way that the various stacks are connected to each other laterally, using specific stowage equipment such as bridge fitting was a typical practice at first. In contrast, today each stack stands alone, allowing it to be packed or unloaded without affecting adjacent stacks.
A ship transporting containers on deck thus transports a kind of “forest” of independent towers that sway back and forth in heavy seas because of the elasticity of the lashing material in much the same way that ears of corn in a field do.
Besides the twistlocks, lashing rods are positioned crosswise in front of and behind each container stack, to absorb lateral stack movements. Lashing bridges, as they are called running across the ship between the rows of containers, are provided to enable workers to stand on to lash higher-tier containers. This facilitates easier lashing of the 5th and higher tier containers, especially for bigger container ships.
Who Is Responsible For Container Securing On Board Ships?
Container lashing, the process of securing containers together on board a ship, is one of the greatest areas of risk in the marine cargo handling sector. It is therefore a task that requires a great deal of expertise and because of the expertise required, the shipowner contracts stevedores to carry out lashing and de-lashing jobs in port. The stevedores might or might not be employees of the container terminal where the vessel berths.
Regulations stipulate ships carry a cargo securing manual that contains instructions on how cargo should be secured in accordance with class standards. Because the approval of the arrangements in the manual presupposes the master uses good seamanship to lessen the forces operating on the cargo stowage arrangements, the master thus retains the ultimate responsibility for securing containers on his/her ship.
The container Lashing is regularly checked by the ship’s crew during the voyage to avoid any type of accidents because of improper lashing. The Shipmaster through the Chief Officer of the ship is, however, responsible for the safe stowage of the containers on ships.
Container Lashing Equipment
Container lashing equipment is used to keep cargo containers in place while they are being transported. Regulations stipulate that all container lashing equipment be approved and listed in the Cargo Securing Manual. There are a few different containers securing equipment, but the most common are twistlocks and lashing bars.
Twistlock is a device used to fix containers. It is suitable for containers installed on decks and hatch covers. The container twistlock ends are mushroom-shaped.
When using twistlock, try to insert the twist locks into the bottom holes of the four bottom corners of the container before pushing the handle Twist the mushroom head 90 degrees to lock the container. There are two types of twist locks: manual and semi-automatic.
The lashing bars are used to secure the container stacks to the ship. Normally it is the second and third tiers that are lashed. The process uses short bars of 2500 mm length and long bars of 4500 to 5000 mm, both with a hook with a swivel at one end and a turnbuckle at the other end.
The hook goes into the hole on the container casting and the other end with the turnbuckle is secured to a d ring welded onto the deck. For higher stacks, the turnbuckles are attached to the lashing bridges.
As boundaries of mega-sized containerships get pushed, a continual focus on preventing container lashing failure becomes even more important. There are now Ultra Large Container Vessels (ULCVs)- the very largest container vessels, capable of carrying almost 24,000 TEUs in service and capable of loading 11 levels on deck.
As a result, the integrity and reliability of container lashing have become of much more concern to ship officers because of higher deck loads, which require more stringent lashing arrangements.
It is therefore critical that ship officers be aware of new lashing arrangements and technologies being deployed such as the RSCS+ enhanced Route Specific Container Stowage that permits heavier and higher deck loads and/or less strict lashing arrangements at certain stowage locations depending on the routes and seasons the ship trades.