Analysis of marine cranes

Marine cranes are divided into two categories according to the movement of the boom: fixed and slewing.

The installation position of the fixed crane boom on the ship is fixed, and the purpose of lifting heavy objects can only be achieved by changing the amplitude forward and backward, and the lifting point must be placed by the displacement of the ship, so its operating efficiency is low and its operating capacity is limited.

The slewing crane overcomes the defect that the fixed crane cannot move left and right by installing a rotatable base. It can not only realize the forward and backward movement of the boom, but also complete the lateral displacement of the hoisted object without moving the ship through the rotation of the turntable. Its maneuverability is much better than that of the fixed crane, especially when transferring the hoisted objects on both sides of the ship.

According to the main structure type, slewing cranes are mainly divided into pedestal cranes, pile-wrapped cranes and mast cranes.

Pedestal cranes are mainly connected to the hull through a rotating pedestal. Due to its huge weight and overturning moment, the slewing bearing mechanism is mostly roller-type. Its pillar is a large-diameter cylinder welded on the main deck of the ship and extends from the deck to the bottom of the ship to form a strong hull frame and cylinder frame, which is convenient for the transmission of huge forces and moments.

Compared with pedestal cranes, the biggest feature of mast cranes is its rotating boom around the mast. The mast is fixed on the pedestal and no longer requires a rotating bearing, which greatly reduces the tail swing amplitude of the crane, giving the crane a smaller space occupancy rate and tail swing space, while saving deck area. Since the mast crane is connected to the hull through a frame structure, the connection is relatively simple, does not require a specific barrel foundation, and does not require a counterweight, which can reduce the overall weight of the crane. 

Pile-wrapped cranes are special cranes installed on offshore self-elevating work platforms, the center of which can pass through the platform pile legs and achieve 360-degree rotation. Compared with general pedestal cranes, pile-encircling cranes have obvious advantages such as "compact design, light weight, small deck area, efficient operation and strong capacity".