Comparing characteristics of RMGs with those of RTGs
There are several varieties of yard cranes used in container terminals and these are mainly divided into two types: railmounted gantry cranes (RMG) and rubber-tired gantry cranes (RTG). Terminal operators must first establish the most suitable operation method for their yard when considering the characteristics of RMGs and RTGs, the main reason being RMGs are equipment operated by railway, while RTGs are equipment operated by rubber tires.
Presently RTGs are widely used around the world for yard operations in container terminals, recently though RMG supply has been on the increase, especially in automated terminals. Despite this increased RMG usage, terminal operators frequently experience difficulties during actual operations, which is due to the lack of previous research into RMG operations. Thus, greater effort and study is needed to solve these difficulties.
Because all yard cranes at Pusan Newport Co., Ltd, where I work, consist entirely of RMGs, I have spent a lot of time studying them in order to help overcome their weaknesses, and also to make them more efficient. The difficulties and countermeasures which I experienced during this period can be expressed as shown in box 1. Ironically, the strengths and weaknesses of RMGs are diametrically opposed with those of RTGs. Therefore, an optimal operation plan must be applied, considering the above strengths and weaknesses to the field through an in-depth analysis on terminal operation conditions and environments.
The ideal situation would be to develop a new-style yard crane which uses only the strengths of both RMGs and RTGs. But because, unfortunately, this is unrealisable right now, the next best course of action is to figure out the most suitable operation methods for currently operated equipment.
The most serious weakness of RMGs is that their electricity supply process is provided by reel cable and they are on a railway. The fact that RMGs move only horizontally, and not vertically, exposes a lot of limitations in field operations which sometimes confuses operators, as many more RMGs are needed for loading export containers than are needed for unloading import containers. They have the ability to stack empty unloaded import containers anywhere, but RMGs must be specifically deployed in order to load export containers on-board ships. This is due to the many restrictions on loading including: stowage plans, port of discharge, weight class, high-cubic container dedicated position, vessel stability, commodity types, etc. If RMG effienciency could not be improved, much more time and effort would be spent in considering these restrictions. This is to say: only the person who can improve RMG efficiency can provide their customers with high productivity and the best service.
Yard separation pattern
Below is presented four kinds of patterns for yard separation, including descriptions and opinions based on the author’s experiences:
Yard separation by grouping
In the ‘Yard separation by grouping’ pattern, yard efficiency is high because, during loading and unloading, RMGs can be operated separately. The downside, however, is that, when located in import areas, RMG efficiency becomes lower than those of RMGs that are located in export areas.
Although terminal operations need more RMGs for loading than unloading, these cannot move vertically. In other words, because RMG efficiency is disproportionate, this pattern is not suitable for RMG operation. The pattern is, however, suitable for RTG operation.
Horizontal separation on each block
The ‘Horizontal separation on each block’ pattern is optimal for double cycling operation because all containers unloaded can be stacked anywhere nearby loading containers. But, because export and import containers are easily mixed on the same bay, yard efficiency is apt to be poor and concentration on RMG is also apt to be broken. Thus, this pattern requires complicated and subtle byard management.
Vertical separation on each block
The ‘Vertical separation on each block’ pattern is unsuitable for concentration-type RMG operation, because export and import spaces are both insufficient. Furthermore, this may cause irregular and inefficient bay mixture on each block, although we can expect equal efficiency on each RMG because the proportion of loading and unloading per RMG is equal.
Diamond-type separation on entire yard
‘Diamond-type separation on entire yard’ is the optimum pattern for RMG operation, as it covers the weaknesses which the afore-mentioned three kinds of patterns contain. Using this pattern, terminal operators can overcome the most serious RMG deficiency, which is that RMGs can not move vertically. This is because only this pattern can make all RMGs’ efficiency equal. Because there are the same number of available RMGs on vertical yard blocks as there are on horizontal yard blocks, these can cover the same volume of stacking space for loading and unloading. It is thought that, through this method, each block efficiency and each RMG efficiency can be equal at the Horizontal separation on each block. same time.
