Mobile Harbour Cranes Explained

Ports are critical nodes in the supply chain mechanism and, hence, the resultant world trade ecosystem. According to standard data, over 80% of the goods and freight transported globally depend on shipping.

The commercial shipping industry is becoming increasingly overloaded, if not buckled, thanks to the escalating needs and demands of the ever-increasing population and the consequential implications for the markets and supply chains worldwide. 

However, at the same time, the fleet size has also burgeoned considerably, giving rise to visible changes in maritime traffic patterns. Thus, it is also imperative that all modern port and terminal infrastructure be commensurate to handling such heavy vessel traffic and colossal volumes of freight and goods daily. 

Ports have evolved considerably over time. Modern ports have state-of-the-art infrastructure and capabilities that add value on all fronts, from equipment to handle bulk cargo volumes to digital integration, automation, and even Artificial Intelligence and Machine Learning. 

In tandem with the evolution and progress of autonomous shipping, green shipping, and smart shipping, ports have also made headway towards the paradigm of smart ports, something already in successful existence. 

One of the most important equipment or components in port infrastructure is the cranage system. Cranes are widely used in any port infrastructure, regardless of their size and the types of cargo they handle, such as bulk cargo and containers.

Cranes are used for many operations, including loading and offloading cargo from vessels, cargo transfer to trucks, railways, other ground equipment, storage and warehousing, etc. 

Moreover, cranes vary widely based on type, size, and utilities. For bigger ports or harbour infrastructure handling larger cargo and in greater volumes, the size and complexity of the cranes used are higher than a smaller port handling a lesser amount of freight, as expected. 

Mobile Harbour Cranes

In this article, we shall have a brief overview of mobile harbour cranes. These cranes are the most common in nearly all ports, harbours, terminals, or Special Economic Zone (SEZ) infrastructure.

By simple definition, these cranes are situated on vessel berths, jetties, wharves, or piers near where the vessels are docked and are extensively used for handling cargo and freight volumes to and from the vessel. 

The most defining feature of these cranes is that they are mobile; in other words, they can move from one place to another. This aids in effectively handling larger volumes of cargo and increases flexibility in operations. 

In the long run, this feature of mobile harbour cranes has a huge economic implication. How? Consider this scenario. At some ports of call, ten vessels are engaged in loading and unloading cargo. The size of the port is more than enough to handle a large number of vessels of different sizes. Now, suppose there is a vessel A that needs to be loaded on an urgent basis.

However, simultaneously, two other vessels, B and C, also need to be offloaded urgently. The size and configuration of the vessels, along with the charter schedules, are such that vessels A, B, and C can be allotted certain berths only. Now, imagine that only one crane is available for these three vessels. The rest of the cranes, say four or five more, are engaged with the other vessels. 

At this point, consider two scenarios. First, the crane available to these three vessels was stationary. What would have happened? The crane would have catered to one vessel only at a time, say A. The rest of the two vessels would have to either- I) wait for the crane to be free after it is done with vessel A or ii) wait for at least two of the other berths to be free so that they can move there and resume their cargo operations. 

The word ‘wait’ translates to more waiting or idle time; in the shipping industry, time is nothing but money. Further, consider that two other arriving vessels, P and Q, were designated for the berths later occupied by B and C in the instance (ii) (assuming they cannot occupy the berths previously occupied by B and C due to technical reasons). 

What happens? These two vessels must remain moored at the harbour till they can find these berths now occupied by B and C, and the loss incurred by the charter companies, the port, the various other stakeholders, and ultimately, the entire supply chain, further stockpiles. 

Now, consider the situation when the crane in proximity to A, B, and C is mobile. It can handle all three vessels in tandem based on requirements by shifting itself from one point to another accordingly. None of the vessels suffer a significant downtime, and all operations at the port remain equable. 

Components and Technicalities

A mobile harbour crane has many components, like a large-scale industrial crane, a set of wheels operated on a rail track laid on the jetty or dock, or a set of normal wheels. With these wheels, these cranes can laterally move from one point to another as and when desired. While going into the details of each part is complicated, let us have a brief overview of the major basic components: 

Boom: The most important component that does the job of lifting. For all mobile harbour cranes, the boom is a long, trussed structure that extends horizontally and vertically and acts as a mechanical arm for lifting the cargo at the ships or the docks.

Modern port infrastructure facilities have cranage with a telescopic boom for all practical purposes, meaning they can extend and rotate freely as required for handling cargo. However, booms may also be fixed, meaning they can go up and down in the vertical plane only for lowering or lifting the cargo and just be a fixed beam like in gantry crane configurations. 

All crane booms have a marked Safe Working Load or SWL rating, indicating the maximum load it can support under the safety limits of design. Booms are heavily strengthened and often require periodic inspection to assess their operability.  

These booms on mobile harbour cranes are either cantilever beams that are supported or hinged at one end and free at the other or are fixed-fixed beams in case of a gantry configuration. 

Jibs are often additional supporting arms or slings that extend from the boom to provide additional strength and support while lifting the cargo. 

Hoist or hooks/ Grabs: The tip of the boom is connected to the hook or grab, depending on the type of cargo. For bulk loose cargo, like in bulk carriers, a bucket-like grab is mostly used for operating the cargo, whereas a hook is used for containers. These hooks or hoist blocks are often lowered below the boom tip using tough slings or cables. 

These grabs or hooks are further shifted and positioned across the boom’s length as required using wheeled or sliding systems trolleys. 

Gantry or column or legs: Depending on the crane’s configuration, a gantry or pillar-like singular column structure supports the boom mounted atop. As shown in the following figure, if the crane is characteristic of two supports in an overhead beam-like configuration, it is a typical gantry configuration where the boom rests on two truss-like legs, known as a gantry structure. 

However, many mobile cranes also have a singular leg-like structure or a column where the boom is hinged and can operate freely in at least 3 or 4 degrees of freedom. Telescopic booms are typical of the single-leg type, where the adjustable boom is hinged about the vertical column and can rotate in any direction as required. This central structure is the other primary member of a harbour crane, along with the boom.

Platform or foundation: For pillar leg or column-like configurations, the entire structure rests on a bottom foundation that essentially transfers all the oncoming loads from the top, as shown. However, a platform is not required for standard gantry cranes as the boom is fixed on two large gantry supports that absorb all loads and transfer them directly to the ground. 

Cabin: The crane must be operated and controlled by a designated operator or personnel sitting in an enclosed room with all consoles and systems. The cabin is always situated above, close to the boom.  

Though modern systems are self-stabilizing and more robust in design, cranes (other than gantry types) often require balancing counterweights placed at the opposite end of the load point on the boom (where the load is acting). 

Electrical and hydraulic systems for all lifting operations. 

Control and electronic systems for sending necessary user-specified signals to the electrical systems during operations. 

Rails, wheels, and chassis: Today, most big cranes run on a set of wheels laid on a rail track. However, smaller mobile harbour cranes are also fitted with normal truck tyres and can move in any direction like a conventional vehicle. 

Conclusion

In modern port ecosystems, these mobile harbour cranes are also evolving dramatically. Automation and digitisation are extensively being implemented in modern products to assist human intervention and increase efficiency. IoT, or the Internet of Things, is one of the key drivers behind the modernisation of port infrastructure, and these cranes are no exception.

However, on the flip side, with more automation and intelligent systems coming into the backdrop, the safety element also comes into question as we keep questioning the reliability of these smarter systems. Mobile Harbor cranes also play a catalytic role in the green deal, encompassing the gamut of logistics and transport by being more energy efficient. 

As these systems are major consumers of energy and emitters of air pollutants, stress is being laid by modern port infrastructure to make the cranage less power consuming, and at the same time, enforce new strategies to reduce idle times, optimise operations, and look out for alternate fuel options. 

You might also like to read-

• What Are Telescopic Cranes?
• Port Gantry Cranes: A General Overview
• 10 Massive Crane Ships Operating at the Sea
• Yoshida: The Largest Crane Ship in the World
• Types of Port Cranes
• 6 Largest Gantry Cranes In The World

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About Author

Subhodeep is a Graduate of Naval Architecture and Ocean Engineering. He has deep interest in marine structures and goal-based design aspects, and is dedicated to sharing and propagating technical knowledge of the industry.

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