Take a load off

04 Oct 2007

At New York Container Terminal there are four truck lanes under each Liebherr crane

The time wasted in positioning containers can be a huge drain on crane resources. David Foxwell seeks advice on how to improve ship-to-shore crane operations

Studies show that the greatest potential for improving container crane performance lies in reducing the time it takes to position the spreader and in container positioning, and that as much as half of a crane's cycle time is spent - or wasted - on load positioning.

Well known features such as high hoist and trolley speeds, which reduce cycle time; and features such as simultaneous hoisting, trolley travelling and gantry travel; plus twinlift operation; tandem lift operation; and advanced crane management software have become standard features on most ship-to-shore cranes, but the search continues for further reductions in non-productive cycle time that can increase performance with marginal additional investment.

Speaking to Port Strategy, Gerry Bunyan at Liebherr Container Cranes in Ireland, says that customers for its ship-to-shore cranes are increasingly aware of the need to try to improve the landside transfer cycle, and reduce unproductive time.

"Positioning the truck or straddle carrier that is going to receive the box is very important," he tells Port Strategy, noting that Liebherr has been using infra-red readers to detect the position, along with a traffic light-like system that gives the driver of a truck or the operator of a straddle carrier instructions about how best to manoeuvre to receive the box quickly and efficiently.

As Paul Bolger, a technical sales engineer at the company explains, the objective of the Trailer/Straddle Carrier Positioning (TSP) system is to enable precise positioning of trailers under crane span for rapid load/unload motions. Laser scanners mounted at sill beam level are employed on each crane, coupled with signal lighting systems for truck drivers at end-carriage level. Each scanner services one truck lane. A signal light mimic panel is also provided in a convenient position in the crane driver's cabin under the driver digital display. At New York Container Terminal, for instance, there are four truck lanes under each Liebherr crane.

"The system software is designed to position 20ft/40ft/45ft and 2 x 20ft containers optimally under the crane," Mr Bolger explains. "In operation, truck drivers position trailers in the service lane target area and a confirmation light denotes optimum positioning for the next crane motion. Gantry truck inching is thereby eliminated and the crane driver can load or unload intensively to the same ship bay.

"The system incorporates several innovations to counteract potential problems due to weather or environmental variation. Feedback indicates that the system works extremely well and makes a valuable contribution to increased terminal productivity."

Additional design features now available on this type of system can automatically detect a crane loading/unloading mode and the system is capable of positioning trailers arriving from either direction. LED direction indication panels are also available as an alternative signal lighting system.

"More and more customers are asking for this kind of thing," Mr Bunyan says, noting that technology of this type had been specified on ship-to-shore cranes, such as at Saqr Port Container Terminal in the United Arab Emirates, where three 45-tonne capacity ship-to-shore cranes were supplied by Liebherr, as part of a wide-ranging upgrade of the equipment at the port, and at Howland Hook Container Terminal in New York. Another facility to have invested in this kind of 'added value' technology to enhance throughput is Forth Ports' Port of Grangemouth in Scotland, where two 40 tonne SWL 32m outreach cranes were recently handed over by Liebherr.

Konecranes, which recently obtained orders from Finnish container terminal operator Steveco Oy for a ship-to-shore (STS) crane and three straddle carriers, notes that in the past, the problem with panamax-size cranes was largely one of accommodating small vessel movements; whereas today the challenge for the latest generation of giant container cranes is that controlling the spreader is made more difficult by greater crane deflections and longer hoisting ropes.

Loading and unloading with panamax-size cranes requires simultaneous (or consecutive) trolley and gantry movements for final positioning. Spreader response is relatively slow, and the positioning problem becomes even more difficult with taller super post-panamax cranes, when the spreader is suspended from longer ropes which do not effectively dampen the pendulum effect.

When not limited by yard operations, notes Konecranes, container crane performance is constricted by two main considerations: the characteristics of the crane, and its load-handling features. Crane characteristics include features such as capacity, speed and acceleration, values that are easy to compare, but actual crane performance is also significantly affected by other factors.

According to a study of several container terminals that Konecranes carried out, as much as 40%-60% of the loading or unloading time of a typical quayside crane is accounted for by positioning the spreader, when for example, the operator is attempting to position an empty spreader on top of a container, or trying to position a container on a chassis or on top of another container.

As Konecranes notes, options are available to tackle some of these issues. Steveco in Finland, which is planning to start container operations at the new Vuosaari port in Helsinki, recently ordered a Kone panamax ship-to-shore crane with Konecranes' 'BoxHunter' technology, a crane that has a lifting capacity of 50 tonnes and an outreach of 38 metres, and allows containers to be stored beneath the crane, which accelerates the loading and unloading process.

The BoxHunter concept provides a number of 'added value' features of the type highlighted above, all of which are designed to enhance the speed and precision of the positioning of containers. Compared with first generation load control systems, claims Konecranes, BoxHunter's auxiliary rope system with independent drives provides new levels of load control - combating sway, skew and the effects of wind - while delivering horizontal fine positioning without trolley or gantry movement.

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