Marine crane can be divided into light and heavy types. Those with a lifting capacity of less than 10 tons are light crane, and those with a lifting capacity of more than 10 tons are heavy crane. The lifting capacity of the marine crane is determined according to the purpose of the ship. Generally, the lifting capacity of light derrick of dry cargo ship is 3 ~ 5 tons for single pole operation and 1.5 ~ 3 tons for double pole operation; The lifting capacity of 10000 ton dry cargo ship can be up to 10 tons by single pole operation and up to 5 tons by double pole operation. In order to load and unload containers on modern multi-purpose ships, the lifting capacity of the marine crane should be able to lift at least 20 feet of containers (20 tons). Heavy suspenders are used to load and unload heavy and heavy goods such as large machinery, locomotives and vehicles. Generally, only 1 ~ 2 marine cranes are set on cargo ships, with lifting capacity of 10 ~ 60 tons, 60 ~ 150 tons and a few of 300 tons. Generally, each cargo hold of a dry cargo ship has two light cranes; Each cargo hold of a giant dry cargo ship is often equipped with four light suspenders.
Machinery installed on the ship’s upper deck. This crane has a compact structure, so that the ship has more deck area to use, and has little impact on the line of sight of the bridge. Deck crane has the advantages of simple operation, high loading and unloading efficiency, flexibility and no cumbersome preparation before operation, so it is increasingly widely used.
Fixed rotary crane, mobile rotary crane and gantry crane are commonly used for deck cranes. There are two transmission modes: electric transmission and electric hydraulic transmission.
Fixed rotary crane
This kind of crane is the most widely used and can operate on the port and starboard separately or in pairs. The lifting capacity is generally 3 ~ 5 tons. On multi-purpose ships, it is required that a single crane can lift 20 foot containers and a double crane can lift 40 foot containers (30 tons), with a lifting capacity of 25 ~ 30 tons.
Mobile rotary crane
When loading and unloading goods requires a large crane span and the crane boom is not too long, mobile rotary cranes are often used. There are two types of mobile rotary cranes: horizontal movement and longitudinal movement along the ship.
This crane is widely used by full container ships and barges, usually quadruped or C-type. There is an extendable boom, a lifting rung, a movable bridge and cab. The horizontal main beam of the bridge is higher than the containers stacked on the deck, and there is an automatic positioning device. When loading, the containers can be accurately placed in the container compartment or stacked on the deck. The number of gantry cranes on the barge is more than that on the container ship, and the lifting capacity can reach hundreds of tons.
Other handling machinery
There are mainly elevators, hoists and conveyors. The elevator is a machine that moves vertically along the guide rail on the ship, which is used for lifting and lowering goods between decks. For example, elevators are often used on RO ro ships to connect all decks to transport goods. There are several kinds of elevators on RO ro ships, such as shear type and chain type, with a length of 9 ~ 18.5M and a width of 3 ~ 5m. Some cargo barges are also equipped with elevators to load and unload cargo barges, but the lifting capacity is much larger than that on RO ro ships. The elevator continuously transports goods in the vertical direction or a large inclined direction. The conveyor continuously transports goods in the horizontal direction or the direction with small slope. These two kinds of machinery are mostly used on self unloading ships or ships loading and unloading through gangways