The largest modern container cranes are classified as ultra-post-Panamax, some having a 120-ton load capacity. The basic structure of portainers consists of the following parts:
- Main boom. The part that hangs over the ship and is vertically retractable. For the stability of the spreader, the main boom must be as close to the maximum stacking height of the ship as possible. This factor may complicate the berthing of vessels, which is why the main boom has a hinge point just above the tip of the quay, allowing it to be lifted. As a result, the ship is not limited by the crane. Manufacturers offer the market a variety of main booms. Low-profile STS cranes exist where the boom can either push forward or extend above the vessel deck. These cranes are suitable for areas with maximum crane height restrictions (for example, near airports) and offer reduced visual impact.
- Trolley. The part of the crane that drives over the main boom. The trolley serves as the supporting structure for both the spreader and the cabin. They have to support the hoisting mechanism and the mechanism that enables the trolley to ride over the main boom.
- Spreader. The device that picks up the containers is mounted on the trolley with cables.
- Cabin. The part of the crane that houses its operator, which can be accessed by stairs or elevator.
- Legs (waterside leg or WS and landside leg or LS). 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, 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 the loading and unloading of the ships, and ensure that the cranes can 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. The second is the electric power provided by the terminal facility from the dock. Most STS cranes are electrically powered and therefore require a connection to a power grid. This connection is realized by huge cables that lie 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 and off the motorized reel.
- Boogie set and wheels. The boogie set is the part of the crane that is under the leg of each corner, meaning that a crane has four boogie sets. Typically, a crane has eight wheels per corner that distribute the weight on the quay.