Size matters

13 Oct 2008

The dramatic result of a ship's unit striking a harbour crane last year. Credit: www.cargolaw.com

Stephanie Knight finds that ship-to-shore crane manufacturers are already thinking beyond the 'standard' 22 container outreach

Everything is going up, it seems. Rene Kleiss of Kalmar admits that although the maximum 'standard' is now a ship holding 22 containers across, "just a couple of years ago we believed that 20 was going to be the widest. Let's just say that sooner or later we may have to rethink".

The rising scale of containerships is dragging the ship-to-shore (STS) cranes into a race involving manoeuvrability, reach, reliability - and interestingly, weight. It was once the norm for ship-to-shore units to have a capacity below the spreader of 30 tonnes: it is now common for that value to be more than 70 tonnes and the overall weight around 2,000 tonnes. However, this 'size matters' approach is affecting more than the cranes themselves.

Paul Bolger of Liebherr explains that a part of the problem can be the quayside itself. It is physics after all - a long boom arm with a weight on the end has to displace force proportionally downward - very often right on the edge of the quay. So, the cost of installing larger cranes on an existing port can rise steeply since piling is only second to dredging for eating up finance, though some cranes, like lattice-constructed units, are lighter than others.

The position that STS cranes take at the very edge of the quay also leaves cranes open to being swiped by anything with a protrusion coming past - not long ago a fatal accident was caused by the flared bow of a geared containership striking a crane. Further, the Swiss Club insurance group noted that damage caused by onboard cranes striking gantry units at the water's edge was one of the most frequent kinds of crane accident, causing extensive losses if the port was unable to use the unit for a long period. However, the safety issues don't stop there: for example ZPMC's port cranes also have to take into consideration more local issues including typhoons and, as in the Port of Los Angeles, both earthquakes and aeroplanes.

But Mr Kleiss says: "It is the operators who provide the most basic level of safety", and it is this human element that can so easily be put under strain from increasing time pressures and complexity of movements - especially as a badly-designed cab can translate these into angles that, over a long shift, would even tire out Hercules.

Luckily, the latest technology aims to reduce both operator fatigue and the possibility of clashing through ergonomic cabs/consoles and anti-collision systems: both of these are now being recommended by port authorities and crane manufacturers as standard. Liebherr also recommend a driver's cabin control which can raise the boom to 45°-60°, allowing for ship clearance and maximising operational time.

Height sensing systems for automatic deceleration of the spreader and truck or straddle carrier positioning systems are now becoming regular features, and also on offer are the new generation of 'sway' controls, which lessen both mental and metal stresses. For example, the SmartCrane system uses pendulum equations to regulate acceleration, correcting sway caused by trolley speed changes and wind or non-vertical lift.

Further, automatic 'parabolic' moves can co-ordinate trolley with spreader height, meaning that the crane head arrives in a 'ready' state at a predestined cell position by the ship, "reducing lift times by 30% or more", says Dr Joseph Discenza of SmartCrane, although it seems the semi-automatic moves can unnerve unseasoned operators.

And since, as Mr Kleiss says, "the overriding priorities are performance and capacity, with price following closely behind", flexibility is also an issue.

While many cranes now have the ability to hoist, trolley, and gantry travel at the same time, there is also the drive, which repositions cranes up and down the berth, usually achieved by rail tracks. Igus, however, install chain drives in continuous trough guides of anything up to a kilometre for the larger ports because, the company says, chain drives wear better than drum winches under the pressure of continuous movement.

However, it should be noted that while the technologies are insistent on shaving seconds from a move, getting it on site takes a lot longer; at present lead times are around 15 to 18 months for Liebherr and 10 to 16 months for Kalmar.

But as for the future, since capabilities like tandem lift have moved quickly from innovation to requirement, Mr Kleiss concludes, "I have learned never to say 'this is the limit'."

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Liebherr Container Cranes

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