The largest modern container cranes are classified as ultra post-Panamax, some having a 120-tons load capacity. The basic structure of portainers consists of the following parts:
- The main boom is the part that is hanging over the ship. For the stability of the spreader, it is essential that the main boom is as close to the maximum stacking height of the ship. This factor may complicate the berthing of vessels, and that is why the main boom has a hinge point just above the tip of the quay in order to be able to be lifted, so the ship has no limitation because of the crane. Manufacturers provide the market with many and different types of main booms. Low profile STS cranes exist where the boom is able either to push forwards or to push in above vessel deck. These cranes are suitable for maximum crane height restrictions (for example, near airports) and reduced visual impact.
- The trolley is the part of the crane that is driving over the mean boom. The trolley is the supporting structure for the spreader and the cabin. Trolleys have to support the hoisting mechanism and the mechanism that enables the trolley to ride over the main boom.
- The spreader is the device that picks up the containers and is mounted on the trolley with cables.
- The cabin is the part of the crane housing its operator. The cabin can be accessed by stairs or elevator.
- The legs (waterside leg or WS and landside leg or LS) of the crane generate the height. The height of the cranes has been increasing over the years due to the increasing stacking height of containers above the ship’s deck (now up to 11 containers above decks and 12 below deck). In general, the WS leg is thicker than the LS leg. This is because the WS leg has to support more moment forces. Legs can be vertical, but some of the WS legs have a slight angle in the LS direction.
- Cable reel and power-supply allow flexibility during loading and unloading of the ships and are necessary for the cranes to move along the quay. STS cranes are commonly powered by two types of power supply. The first is a diesel engine-driven generator located on top of the crane and the second is electric power provided from the dock by the terminal facility. Most STS cranes are electrically powered and therefore need to be connected to a power grid. This connection is realized by huge cables that are lying in gutters over the quay. The voltage that they require may range from 4,000 to 13,200 volts. When the crane needs to move, the cable must roll on roll off by the motorized reel.
- Boogie set and wheels support the crane on the quay. The boogie set is the part of the crane that is under the leg of each corner, meaning that a crane has 4 boogie sets. Typically, a crane has 8 wheels per corner. The total loads of one corner need to go through the 8 wheels. If the quay is insufficiently strong, cranes with more wheels per corner can be made.