These ships carry cargo in containers. Goods are locked and sealed in huge boxes of the standard size. Containerships carry containers both in holds and on the main deck. In the holds, there is a special cellular structure of guide rails where containers are stowed one on the top of another. That is why they can be also called cellular vessels. These ships usually have one deck, with the machinery spaces located towards the aft end. Additional containers are stowed on open deck and anchored in place by wire ropes. Containerships have made a revolution in water sport. The higher speed of around 26 knots is their main advantage over other cargo ships. In addition, the loading and unloading work with the use of shore based moving gantry cranes is extremely fast. The primary advantage of the use of containers is the possibillity of transporting cargo directly from customer to customer, not only from port to port. Container vessels have grown in capacity up to 8000 TEU. Large containers vessels usually do not have thei own loading gear. However, small or medium-sized ones, called container feeders, are often equipped with cargo gear. Also, some multiporpose ships can operate as container feeders.