Scratch the surface

05 Dec 2007
Port Strategy: MTL describes RMGs as an "essential cog" in terminal operations

MTL describes RMGs as an "essential cog" in terminal operations

There's a lot more to RMGs than meets the eye, not least a proven track record in container handling, as Alex Hughes discovers

On the face of it, there appear to be few reasons for buying rail mounted gantry (RMG) cranes, where the obvious alternative - the rubber-tyred gantry crane - seems to hold all the advantages.
RMGs are more expensive, are restricted in terms of movement and have higher civil and electrical engineering costs. In addition, their gantry travel distance is limited by track length and high tension supply cable. Being a rail-based system also means RMGs are more sensitive to settlement and much more efficient monitoring of the stacking operation is required to avoid excessive shuffling.

But, and this is a big but, running costs for RMGs are substantially lower, since no power is consumed when the RMG is idle and regeneration is also a major cost saver. Tyres, in particular, which are notoriously expensive to replace and getting harder to source, are not an issue. Wider and higher stacking possibilities also result in increased yard capacity, while the machines themselves can achieve faster long and cross travel speeds when handling full containers. The RMG also operates on an inherently more stable platform, which results in more accurate and faster stacking, and they are easier to automate.

And there's more: environmentally, the RMG is also a good bet. RMGs have fewer emissions and emit less noise. They are easier to maintain and being electrically driven are less prone to breakdowns. In cold weather, there are no worries associated with cold starting, while drives overall are more responsive.

And for those operators will long, thin yards, RMGs are a no-brainer: they can operate in areas where RTGs cannot even penetrate.

Port of Dublin container stevedore, Marine Terminals Ltd (MTL), operates four Liebherr RMGs.

MTL maintenance manager Gary Malone explains that the RMGs have become an essential cog in the overall operation of the terminal. Machine reliability is therefore a key component in ensuring maximum productivity. Nevertheless, there are times when these vast machines do require attention, so service areas have been created within the container stacking bays to allow maintenance and repair to be carried out without affecting operations.

"The RMGs have proven to be very reliable," says Mr Malone. "We have continued to perform essential maintenance procedures since the cranes were commissioned in 2002; this has involved things such as replacing DC motor brushes, greasing bearings and pins. To minimise crane downtime, we schedule these procedures to take place over several days, keeping stoppages to a few hours at a time."

However, major things such as hoist rope changes and twelve monthly service schedules require co-operation from operations to allow sufficient crane downtime for these procedures to be completed.

According to Mr Malone, the terminal keeps both paper and electronic records pertaining to all its RMG maintenance procedures, with all scheduled maintenance also tracked. Regular inspection on serviceable parts is undertaken monthly across all terminal equipment, with certified components logged on installation and on removal.

"I can't stress the importance of preventative maintenance; this is essential on all plant to ensure that it operates at maximum productivity," he says.

Liebherr recommends three, six and twelve monthly service procedures, which Mr Malone stresses his team tries its best to adhere to. However, in the shipping industry, other elements such as tide and weather come into the equation, he concedes, so there is a delicate balance to be struck on occasions between maintenance and operations.

"We implement our own monthly service schedules to try to prevent even the smallest of problems," he adds.

Asked whether any features on the RMG fleet helped make maintenance easier, Mr Malone points out that access to all serviceable parts on the units has been made very simple thanks to the input from Liebherr's engineers.

By far the most interesting comment made by Mr Malone, however, concerns the fact that Marine Terminals' RMGs are driven by a 10kv HT supply through a cable reeling drum. This, he stresses, drastically reduces maintenance required compared to using diesel power.

"If you compare an RTG with an RMG, the former could be said to be a version of the latter, but with a diesel engine and a generator strapped on board. These are components that clearly require additional servicing and/or repair. Our cable reeling drum effectively does away with these additional complications on an RMG. RMGs also don't have tyre replacement issues or punctures. As a result, I believe RMGs are easier (and therefore cheaper) to maintain when compared to RTGs, since there are fewer overall components on the machine," says Mr Malone.

But isn't there an additional cost involved with rail maintenance on an RMG? Apparently not: in the five years that the RMGs have been in Dublin, rail maintenance costs have so far been zero.

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