In the field of port machinery, marine cranes play a crucial role as core equipment for ships engaged in cargo loading and unloading operations. Also known as marine cranes or derricks, they are primarily installed on ships to handle various types of cargo, and are regarded as the most important deck machinery for ship production operations. These cranes feature a compact structure, an attractive appearance, safety, reliability, energy efficiency, environmental friendliness, and excellent maneuverability. Their booms come in various forms, including straight booms, telescopic booms, and folding booms; and their power source control methods are diverse, such as manual, electric, and electro-hydraulic.
Marine cranes are special equipment that perform transportation operations in the marine environment, undertaking important tasks such as cargo transfer between ships, offshore supply, and deployment and recovery of underwater operation equipment. However, the special marine application environment poses significant challenges to the control of marine cranes. On one hand, similar to land-based underactuated crane equipment, they need to control the swing of the load during transportation to ensure positioning accuracy and transportation efficiency; on the other hand, since cranes are fixed on moving platforms such as ships, the movement of the platform will strongly affect the movement of the load, and in many cases, the movement of the load's lifting and landing points is often different from that of the crane itself. During operation, both the crane ship and the receiving ship will pitch, roll, and heave due to ocean waves, causing the load to swing. During lifting and lowering, the ship's movement can easily cause the lifted load to collide with the deck again, or cause the load that has been lowered but not yet detached from the hook to hang in the air again, threatening operational safety. Especially during ammunition supply between ships, such coupled movement may lead to more serious consequences. Therefore, the control of marine cranes has attracted widespread attention from military and civilian marine engineering sectors worldwide, and researching the control of such nonlinear, strongly coupled underactuated systems under special disturbances is of great theoretical value and universal significance.
The control of marine cranes mainly focuses on two aspects: vertical control to reduce the impact of hull movement and lateral anti-sway to suppress load swing. For vertical control, a common method is to connect the receiving ship through the mechanical structure of the crane ship, sense their relative movement, and synchronize the change in the length of the lifting rope with the heave movement of the receiving ship, thereby compensating for the relative movement between the two ships and completing the lifting and transportation of the load. However, this method has special requirements for the mechanical structure of the crane and imposes significant restrictions on the lifting weight.
Composition and Operation Modes
In terms of components, the derrick device is a traditional cargo handling equipment, consisting of a derrick, a cargo boom (or cargo mast), rigging, and a winch (or cargo winch), etc. Despite having numerous ropes and being cumbersome to operate, it has been widely used due to its simple structure, ease of manufacturing, and low cost. There are two modes of loading and unloading cargo using the derrick device: single - boom operation and double - boom operation.
Single - boom operation uses one derrick to load and unload cargo. After lifting the cargo, the guy rope is pulled to make the cargo swing with the derrick to the outboard or the hatch, then the cargo is lowered, and the derrick is rotated back to its original position, repeating this process. Each time, the derrick needs to be swung with the guy rope, resulting in low efficiency and high labor intensity. Double - boom operation uses two derricks, one positioned above the hatch and the other extended over the outboard. The derricks are fixed in a certain working position with guy ropes, and the hoisting ropes of the two derricks are connected to the same hook. By respectively retracting and releasing the two hoisting ropes, cargo can be unloaded from the ship to the dock or loaded from the dock onto the ship. The loading and unloading efficiency of double - boom operation is higher than that of single - boom operation, and the labor intensity is also lower.
Improved derrick devices emerged later. The double - topping lift derrick device is improved from the single - boom operated derrick device, with only the hoisting rope and two sets of left and right separated topping lifts. The derrick is controlled by one hoisting winch and two topping lift winches, which is easy to operate and has high loading and unloading efficiency. The Abel derrick device is improved from the double - boom operated derrick device, with a hoisting winch, topping lifts, and guy rope winches. It can quickly position the derrick at any position with the help of the winches and can also lift and lower cargo at fixed points within the working radius of the derrick, which is an important step towards full automation of cargo loading and unloading.
Applications and Structural Characteristics
Marine cranes are widely used in bulk carriers, container ships, oil tankers, multi - purpose ships, etc. Such as cargo cranes on bulk carriers and container ships, hose cranes on oil tankers, and deck cranes on multi - purpose ships. Compared with land - based cranes, marine cranes are installed on unstable ships. During operation, the ship will tilt and sway, and the working environment is harsh, subject to erosion by sea wind and seawater; even when not in operation, they need to withstand external forces such as wind, snow, waves, swaying, heaving, and impact during the ship's navigation.
They come in various structural forms, including jib slewing type, traveling type, wire rope luffing type, cylinder luffing type, telescopic boom type, folding boom type, A - frame type, and composite type; and there are various driving methods, including electric, electro - hydraulic, electro - pneumatic, gasoline (diesel) engine driven, and manual driven, etc. A typical example is the electro - hydraulic marine crane used for cargo loading and unloading on bulk carriers.
The load - bearing structures of marine cranes, such as the base column, tower body, and jib, are mostly welded structural parts made of metal steel plates. The lower part of the base column is welded to the ship's hull to bear the gravity load of the crane, and the upper part is equipped with a slewing bearing; the tower body is a supporting structure, with its lower part connected to the slewing bearing and hinged to the jib, the upper part has pulley block steel wire ropes moving, the interior is used as a machine room, and the cab is located at the front; the jib is a truss - like structure used to support heavy objects.
The executive mechanisms of marine cranes include the hoisting mechanism, luffing mechanism, and slewing mechanism. The hoisting mechanism realizes lifting by the motor driving the drum to rotate through a reducer, retracting and releasing the steel wire rope to make the hook move up and down; the luffing mechanism makes the jib rotate up and down around the lower hinge point to change the angle by the motor driving the drum to rotate through a reducer, retracting and releasing the steel wire rope, so that the hook can luff at different amplitudes; the slewing mechanism makes the tower body and jib rotate by the motor driving the pinion to mesh with the large gear of the slewing bearing through a reducer. The reducers of these three mechanisms are all equipped with normally closed brakes to ensure the normal operation of each movement. Through the coordinated operation of the three mechanisms, the load can be lifted and placed at the required position within the working range.
The electrical system for driving and control is composed of various control components in the electric control box to form a control system, which is operated and controlled through buttons and handles on the console on both sides of the cab seat; the hydraulic system is composed of pumps, motors, valve groups, pipelines, and their accessories to control and drive some executive mechanisms. In addition, marine cranes are also equipped with auxiliary devices such as passages and ventilation devices.
Classification and Other Loading and Unloading Machinery
The derrick devices of marine cranes can be divided into light - duty and heavy - duty types. Those with a lifting capacity of less than 10 tons are light - duty, and those with a lifting capacity of more than 10 tons are heavy - duty. The lifting capacity is determined by the purpose of the ship. For general dry cargo ships, the lifting capacity of light - duty derricks in single - boom operation is 3 - 5 tons, and in double - boom operation is 1.5 - 3 tons; for 10,000 - ton dry cargo ships, the lifting capacity in single - boom operation can reach 10 tons, and in double - boom operation can reach 5 tons. Modern multi - purpose ships need to load and unload containers, so the lifting capacity of the derrick must be at least able to lift a 20 - foot container (20 tons). Heavy - duty derricks are used to load and unload heavy and large cargo such as large machinery and locomotives. Generally, 1 - 2 heavy - duty derricks are installed on cargo ships, with a lifting capacity of mostly 10 - 60 tons, some 60 - 150 tons, and a few up to 300 tons. Each cargo hold of a general dry cargo ship is equipped with two light - duty derricks, and each cargo hold of a giant dry cargo ship is often equipped with four.
Deck cranes are installed on the upper deck of the ship, with a compact structure, allowing the ship to utilize more deck area, and having little impact on the visibility from the bridge. They are easy to operate, have high loading and unloading efficiency, are flexible, and require little preparation before operation, so they are increasingly widely used. Common types include fixed slewing cranes, mobile slewing cranes, and gantry cranes, with transmission modes of electric transmission and electro - hydraulic transmission.
Fixed slewing cranes are the most widely used, which can operate on the left and right sides alone or in pairs, with a lifting capacity of generally 3 - 5 tons. On multi - purpose ships, a single crane needs to lift a 20 - foot container, and a double crane needs to lift a 40 - foot container (30 tons), so their lifting capacity can reach 25 - 30 tons. Mobile slewing cranes are used when the cargo loading and unloading requires a large span and it is desired that the crane boom is not too long, with two types: moving transversely and longitudinally along the ship. Gantry cranes are widely used in full container ships and barge carriers, usually of four - legged or C - type. They have an extendable boom, a lifting beam, a movable bridge, and a cab. The horizontal main beam of the bridge is higher than the containers stacked on the deck, and is equipped with an automatic positioning device, which can accurately place the containers in the container grids or stack them on the deck during loading. There are more gantry cranes on barge carriers than on container ships, with a lifting capacity of up to several hundred tons.
In addition to marine cranes, other loading and unloading machinery mainly include elevators, hoists, and conveyors. Elevators move vertically on the ship along guide rails, used for lifting and lowering goods between decks. For example, roll - on/roll - off ships often use elevators to connect various decks for transporting goods, including scissor - type and chain - type ones, with a length of 9 - 18.5 meters and a width of 3 - 5 meters. Some barge carriers also use them to load and unload barges, but their lifting capacity is much larger than that on roll - on/roll - off ships. Hoists continuously transport goods in the vertical or large inclined direction, and conveyors continuously transport goods in the horizontal or small slope direction. These two types of machinery are mostly used on self - unloading ships or ships loaded and unloaded through Side door.
With their diverse structures, rich functions, and characteristics of adapting to different scenarios, marine cranes have become indispensable key equipment in ship operations. With the development of ship transportation and marine engineering, they will continue to advance in terms of efficiency and intelligence, continuously contributing to efficient marine transportation and operation.
Post time: Aug-08-2025
