As the number of containers carried by container ships continues to rise, ship-to-shore (STS) cranes need a radical change to keep up with port calls averaging 10,000 TEU and beyond in size. An innovative multi-trolley concept tackles quayside challenges by complementing existing designs in a symbiosis of scale.
The end of STS crane evolution is confirmed when we look at the obstacles inherent in containership design. Economies of scale require more and more containers to be placed onboard. To date, naval architects have lengthened the vessel up to 400 meters while restricting the increase in the width of the beam. They point out that going beyond this length in the standard design of a container ship is not advisable because it could lead to insufficient torsional stiffness, leaving aside the question of maneuverability.
Taking another path by increasing the width of the beam runs directly into another limitation of ship-to-shore crane design. It is improbable to extend the crane boom forever. Moreover, the speeds of rope-driven trolleys today (250m/min and more) are such that their travel mechanisms put great strain on their ropes.
As the number of containers carried by container ships increases, the size of the average port call is increasing up to 10,000 TEU per call and more. The pressure to unload and load these huge vessels as quickly as possible is greater than ever – but there is a limit to how many adjacent cranes can service the vessel. Quayside productivity has not increased significantly despite all attempts to develop faster trolleys that can carry more than one container per move.
In the big picture, the ever-growing quantity of containers to be transported requires that container terminals grow in size, with longer quays to receive ships, taking more of the available coastline. This poses a significant environmental problem that, accompanied by other factors such as increased air and noise pollution and traffic jams, should be dealt with in parallel.
In the big picture, the ever-growing quantity of containers to be transported requires that container terminals grow in size, with longer quays to receive ships, taking more of the available coastline.
The Multi-Trolley STS Crane Concept
With the current STS concept, the largest productivity constraint is operation on only one side of the ship, with all of the potential consequences described earlier.
The new, multi-trolley STS crane concept that we propose would work on both sides of the ship. It was initiated by the desire to create an ideal quayside crane match for the new ultra-large container vessels. The design goals are:
- To significantly increase berth moves in comparison with the best STS technology available today
- To substantially reduce the number of cranes servicing the ship without detriment to productivity (operational flexibility, maximum utilization rate of equipment, reduced cost of initial investment, reduced energy consumption and reduced maintenance cost)
- To improve crane stability and substantially reduce quay loads and foundation requirements (especially on the waterside), bringing a significant cost reduction to the crane runway
The new crane concept is designed to eliminate the current unloading and loading process bottleneck with a double beam portal crane design (Figure 1) that can service the ship from both sides and that, for the first time ever, can work simultaneously on two bays of containers. The concept is planned to enable installation of two trolleys per beam, which not only greatly increase productivity but also shorten trolley travel, thus reducing the current need for high trolley speed.
The concept calls for a ship berth in the shape of an indented berth. This enables the crane to be supported symmetrically along the longitudinal centerline of the ship, thus reducing the load on the crane foundations.
The new crane concept is designed to eliminate the current unloading and loading process bottleneck with a double beam portal crane design that can service the ship from both sides and that, for the first time ever, can work simultaneously on two bays of containers.In comparison with a traditional STS crane, the new crane would have similar hoist speeds and a reduced trolley speed of 125m/min accelerating in 4 seconds, resulting in approximately 135 seconds per move – for one trolley. This is multiplied by four trolleys on the crane, giving a comparable production of 106 moves per hour.
The crane concept with two parallel beams can match vessel bay spacing, overcoming the constraint of crane width. The output of three cranes would be 7,600+ moves per berth in 24 hours, this without considering the impact of multiple lifts already utilized with current STS cranes.
The new crane concept is designed to provide many advantages over traditional STS design:
- Reduced trolley travel speed without a loss of output (reduced energy consumption, less maintenance downtime and cost, less noise)
- No restrictions on combined trolley loads, exceptional performance in heavy-lift situations
- There are no trolley rail joints (less maintenance, less noise) so the steel structure suffers less fatigue (longer crane life, less downtime, reduced maintenance cost)
- There are dampening measures, giving the potential for a longer lifetime to the crane and crane runway
- Better aerodynamic performance as a result of the shape and shielding of the parallel beams and the absence of stays suspending the boom and upper structure (reduced foundation cost, reduced corrosion)
- Use of new materials to help reduce crane mass and corrosion
- Use of remote operation and automation technology, good load control and positioning
A platform for further STS evolution
The new crane concept is not meant to replace current STS cranes, but to complement them in a symbiosis of scale. Attempting to further evolve current ship-to-shore crane design is unlikely to solve the handling problems that the industry faces (this is also the assessment of Drewry, Ref. 1). Thus, it is prudent to evaluate an integrated approach that covers the crane, the terminal, and ideally even the ship. Together with our partners we are making progress in all three areas.
The new concept also provides a platform for further STS evolution. This point can be illustrated by the crane design. A variant of the present concept was created by slightly increasing the distance between the two beams, and creating space for a third beam running in the mid–plane of both legs. Such a crane would operate over 3 adjacent bays.
Introducing such a third beam could give an increase in output of up to 50% on top of the output of the two-beam crane concept. In practical terms, this means that two cranes, instead of the presently envisaged three, could service a ship with identical output.
This could significantly decrease the initial purchase price, without mentioning other cost reductions that could be enjoyed thanks to the triple-beam crane concept.
This article is an abridged version of the original paper which appeared in Port Technology International.
Text: Vladimir Nevsimal-Weidenhoffer
Consultant: Dr Hannu Oja, Director Port Technology, Konecranes
Vladimir Nevsimal-Weidenhoffer, M.Sc. (Hons.) Civil Engineering, has a long track record in crane engineering, refurbishing and project management, focusing on Goliath cranes for shipyards and grab unloaders. He holds several patents and is the inventor of the Cofastrans quayside crane concept described in this article.
Dr (Tech) Hannu Oja is Director of Port Technology at Konecranes and is responsible for technology, product development and engineering activities within Konecranes Port Cranes. He has contributed in the European Committee for Standardization (CEN) crane standardization workgroups and participated in many university research programs.
1. Drewry Maritime Research: Who will pay for a port productivity revolution?
2. New multi-trolley STS crane concept: PCT patent n° WO 2017 / 071736 A1