Episode 15: How does a twistlock work?

The word is made up of the words “twist” for twisting and “lock” for locking.

In other words, a technique that creates a lock by twisting. This is the basic principle, of which there are of course various variations. In this specific case, we are talking about twistlocks, which are used in container transportation.

Before the container can be stowed on deck, the twistlocks must be manually inserted into the corner castings from below and armed.

Only the containers that are stowed on deck need to be connected to each other with twistlocks.

This is not necessary for containers in the hull because they are held in the stack by the cell guides.

Types of twistlocks

There are basically two different types of twistlocks. These are the manual ones, which must always be closed and opened manually, as the following example shows. They are often used for container stowage on land.

The second version is semi-automatic and is used for stowing on ships. The yellow tip must always be at the top. The twist lock is inserted manually from below into the corner castings and locks automatically.

How a twistlock works

As soon as the container is placed on top of another and the lower tips of the twistlocks come into contact with the corner castings, they twist, tension a spring and slide down into the corner casting.

If all four twistlocks are correctly seated in the corner casting, the spring is relieved and pushes the tip into the locking position.

To unlock, the orange button with the steel cable must be pulled out manually, e.g. with a rod, on all twistlocks and locked to the frame of the twistlock.

This tensions the locking spring and the twistlock tip rotates into the unlocking position.

The container can then be lifted with the spreader.

As there is still no reliable automated solution, the lashers have to work around the clock in all weathers. To do this, they are moved over the containers with a work platform suspended from the spreader to unlock the twistlocks.

The twistlocks are designed for a load of 50 tons each and weigh approx. 6.3 kg. The picture shows the enormous loads that the twistlocks have to withstand in the event of an accident.

Yours, Sigurd Ehringer

Tobias Kreft