The second generation
02 July 2014
To begin with - a bit of history. The birth date of heavy gantry cranes, later called “Goliath” because of their size, happened before 1960. At that time the shipbuilding industry in Europe underwent major technological change aiming at more rational and faster construction processes.
The basic idea was to fabricate large sections outside the dock in a streamlined, sheltered production zone. Then these sections were to be moved on multi-wheel transporters, specially developed for this task, to storage zones next to the dock; there they would be picked up by a crane and positioned inside the dock next to the other sections of the hull under construction where they would be welded into place. This method had many advantages - the best proof being that it is still used today.
Parameters such as width of the dock, requirement to pick up the load (section) from all four sides of the dock and place it anywhere inside it, the height of ships to be constructed, estimated mass and size of sections to be lifted etc, finally resulted in the decision to produce a large gantry crane. This crane would replace jib and hammerhead cranes, which were until then dominant in naval construction.
Designs of this first generation of crane appeared from numerous suppliers on the market, firstly in Europe. Of these designs only two survived (refer to Annex 1 & 2), and of the original suppliers none survive to this day. The two design concepts later spread to Asia, with the Krupp concept going to Japan and the other design to Korea; finally both appeared in China, and are still used there today.
In today’s market, the Krupp design is in the hands of one supplier in Europe, whilst the Jucho/PHB design is in the hands of another, who skilfully modified the original concept by moving the hoisting systems directly onto the trolleys. The author’s knowledge of present Asian suppliers is limited but numerous exist in Japan, Korea and China.
Turning to dimensions and capacity, the span started at 40 to 60 metres, later increasing from 80 to 140 m. Today they go beyond 200 m. In lifting height they started with a maximum of 60 m, later increasing to 80 m and now heights go beyond 100 m.
Lifting capacity began at around 150 to 300 tonnes, and later progressed to 900 or 1,000 tonnes. Current designs have capacities of 1,500 tonnes plus.
(Note: As a point of interest it is to be mentioned that a dimensionally futuristic crane was built by PHB in 1974 having a span of 176 m, lifting height of 114 m and capacity of 1,500 tonnes. It remains in operation - after transfer from Europe to Asia - and dimensionally fully complies with today’s requirements.)
There are two points of importance to be mentioned. First, in the early days, a concept of coupling two cranes to achieve doubling of lifting capacity appeared on the market. Its success was short-lived because its runway, even if constructed with one foundation beam on each side, required altogether four rails. The consequence of this was higher cost of installation plus maintenance cost of the runway, which was doubled. It is also difficult to see why two cranes of X capacity should be cheaper than one crane with the two times the capacity (apart from doubling of maintenance and of operator cost).
On the other hand, some advantages could be found in lesser energy consumption in long-travel and in the possibility (in twin configuration) of partly rotating the load in its horizontal plane. It is believed that some of these systems are still operational in Asia where their lower mass could be of advantage in earthquake locations.
The second point of prime interest concerns the capacity of the long-travel track. With the first installation of a Goliath crane in a given yard its wheel loads, indicated by the designer, provided loading parameters for the runway to be built accordingly. In another words, it was the crane design that dominated design of the runway. Later we shall see that for cranes of the second generation, in many instances precisely the opposite will be the case and we shall examine how this situation affects the crane design.
The first construction wave of these cranes lasted roughly between 1960 and 1980. After a gap of about 20 years, the second wave came in at the end of the 1990s and lasted until the world financial crisis in 2008.
This short time frame was because equipment was required to be updated equipment due to the increase in the size of ships to be built (lifting height). Further rationalisation of construction furthermore called for larger building blocks, which resulted in a requirement for increased lifting capacity. The emergence of new yards in China and Brazil, plus calls for construction capacity increase in Korea, also affected manufacturing, along with the limited modernization of yards in areas such as Germany and Japan.
Where did these cranes come from?
The second-hand crane market in European yards, many of which are now closed, was wiped clean by transfers to Asia. As far as new cranes are concerned, these were built based on the two surviving concepts, by European and Asians suppliers; many in co-operation between the two groups.
What is important and surprising at the same time is that (electrical equipment aside) there was hardly any innovation to speak of, despite roughly 30 years between the two design waves.
Evidently, a regrettable loss of opportunity in these new installations can be explained by the irreplaceable loss of experienced staff due to disappearance of many suppliers and non-replacement of personnel over the 20 years of production gap. Satisfaction of remaining suppliers derived from disappearance of much of competition also caused complacency in further development.
An increase in Asian suppliers, but with little contribution in development, also caused this lack in development, whilst many yards where these new cranes were installed were either new or without such cranes in previous operations. Hence, the all important factor of load capacity of (existing) runways rarely emerged, thus delaying the inevitable process of recognition of its influence on future designs.
The road map
Earlier we stated that there was hardly any development to speak of in this group of cranes since their conception. By that we aimed at principal development e.g. of concept and, in consequence, of the structure. On the other hand, developments of the electrical system have been significant, but as they are common to other cranes as well, they will be dealt with separately.
Even in mechanical equipment there were developments, but these were limited to components (brakes, ropes etc.) As such, they are only marginally represented in the overall context and for that reason shall not be subject of this paper. (Nevertheless, ideas exist but due to their potential patentability cannot be disclosed at present.) Let us therefore commence with future concepts and their expression in the structural part.
The two existing concepts mentioned previously and described in annex 1 have been around for at least half a century. Is this a reason to subject them to doubt or to dismiss them completely? Definitely not, because not only are they are creation of great minds and great experience. But they have been tested for decades and competed successfully with all other concepts on the market.
To an unequal degree their potential for further development is not exhausted, but is there a need to compare them against each other before we move ahead? No, because KRUPP did so already (ref. 1) decades ago. While their evaluation is not entirely faultless, it is grosso modo correct and fair.
What then to say about the two concepts today? Firstly, that likelihood of emergence of a new concept, radically different from these two, is small; moreover, what was invented cannot be reinvented. Secondly, in their own ways they both have a future role to play, as we shall demonstrate later.
What then are the requirements for future development steps from today's perspective?
The following points have to be taken into account, including the 50 year gap between technology and requirements; cost of operations; cost of maintenance; more stringent environmental standards; safety aspects and consequences of inadequate (existing) runway capacity, if and when applicable.
Let us now examine the individual points closer:
While many consequences of this gap are covered by points two to six mentioned above, the basic problem is that this first-class equipment is 50 years old. Under normal circumstances this situation would be unacceptable.
Changes could come from new materials that are stronger, lighter and corrosion-resistant; new design approaches and simulation tools, for example in aerodynamic performance and changes on wind loads, which are in the majority of cases, responsible for fatal accidents with these cranes. Moreover, better aerodynamic performance means less corrosion (every decrease in turbulence means increase in durability of the paint).
Growth in size of section may call for increased distance between hooks (of the same trolley), especially if soft panels are involved. Heavier sections requiring heavier cranes have in consequence more impact during long travel, thus increased loading of the crane travel system and of the track; hence manifest interest to reduce these forces.
The following suggestions for change include lower mass of the crane plus lower aerodynamic resistance during long-travel result in savings in energy; majority of loads during ship construction are between 5 and 40 tonnes. Consider alternatives to using returning trolley for these lifts and displacements with savings in energy and wear in consequence; lighter lifting accessories resulting in increase in useful load capacity; and manpower - is the crane driver indispensable?
Corrosion alone represents 60 % of maintenance effort; therefore it has to be reduced to a minimum, first of all by corrosion-avoiding design. Of equal importance are corrosion resistant materials, maintenance remaining as the third line of defence.
Cranes should also be supplied with light-weight, corrosion resistant scaffolding, for maintenance of the main beam. Design of scaffolding in combination with hoisting mechanisms of the crane should be such as to permit installation, movements and dismounting of the scaffolding by the crane itself (mobile cranes are expensive!) A service crane, if any, should also be well protected against corrosion and enjoy maximum flexibility of movement and application.
Access conditions should also be optimized (lift well starting as low as possible), without being excessively generous; and the number of long-travel wheels should remain limited by mass reducing design and optimal aerodynamic performance. Models could also have suitable design arrangements for easy collection of excess oil and grease.
Regarding the crane, changes include optimum securing of crane and trolleys under storm-wind conditions; efficient load monitoring system (magnitude and positioning); avoidance of excessive application of overload tests; and regular inspections with disciplines followed up.
For the personnel, new designs could have easy evacuation arrangements in case of fire; optimum fire control and fire suppression arrangements; corrosion control of access structures or application of corrosion resistant materials; and solid and regular maintenance of all means of vertical transport, as well as all other mechanisms influencing safety of personnel.
As the ships grow larger and higher, the requirement for goliath cranes is an increase in lifting height. Equally, as productivity drives workshops to come up with ever larger sections (with corresponding reduction in their number per ship), increase in lifting capacity is also required. As ever larger sections have to be lifted, there may be requirement of increase in distance between hooks of the (same) trolley.
To summarise, all three requirements point towards a new crane with corresponding increase in mass and in wheel loads. So, how do you counter that if you have an existing runway originally designed for a smaller crane of the first generation?
First, let us state a fact that to increase capacity of the runway by reinforcing it is out of question. This is not only a problem of cost that, most probably, would be in excess of the cost of a new crane, it is also a matter of disruption to the production. This is the same if you decide to build another runway next to the existing one.
The obvious solution is to increase the number of wheels of the long-travel system. Simple as it appears, it has three principal disadvantages:
Firstly, the higher the number of wheels per corner, the longer, higher and heavier will be the "pyramid" of the equalizers to support them; in a way a self-defeating effort. As a consequence, the longer the long-travel system, the bigger the corresponding loss of serviceable space will be at each end of the runway; or in- between two cranes installed on the same runway. In addition, this situation will increase wear of wheel flanges as sensitivity of the whole system to crabbing and lateral runway imperfections will be magnified. Finally, the higher number of wheels, the higher the cost of maintaining them. The alternative is to fight the increase in mass, which is a question of design and materials.
The second approach is improved aerodynamic performance (each decrease in aerodynamic resistance resulting in decrease in the overturning moment) of the crane with resulting reduction in wheel loads. Admittedly, neither is an easy task given the scenario described previously, but not only can it be done, it is equally the only rational solution.
From trends to design
Chapter 3 summarised author's views on future needs. Their practical expression can be found in concepts SP2000/SP2000A (ref. 2); their international patent proceedings being currently in progress. To examine these concepts in detail is beyond scope of this paper; that would require a detailed presentation with a discussion during and after such event.
Nevertheless, let us state clearly that some principal features of currently marketed first generation cranes have been sensibly retained. The SP2000 concept is based on a twin-beam design, the SP2000A on a mono-beam design; the difference in approach justified by somewhat different mission of each variant. On the other hand, concept of all members below the beam bottom line is identical for both variants.
Further, the author does not wish to hide his opposition to concepts with more than two trolleys on the crane, finding this expensive in procurement, operation and maintenance when compared with additional benefits such solution may offer.
It appears desirable, however, to make specific observations regarding these concepts that go beyond their description in the patent documentation.
In case of SP2000 crane (intended lifting capacity 600 to 2,000 tonnes - concept aimed at large, sophisticated yards for a key role there). The service crane to be mobile and fully sheltered (if out of operations).
There are several reasons for this approach. Firstly, current fixed service cranes have very limited application and as such represent costly investment; hence the idea of making the crane an active piece of equipment. Moreover, installed in a position permanently exposed to inclement weather they require (to assure their all-round readiness) continuous attention by maintenance.
Further, mobile service crane of adequate capacity offers optimum flexibility for maintenance tasks; eliminates need of large capacity hired telescopic cranes required (even for small loads) due to considerable height of the SP2000 crane (needless to say, such cranes are expensive to hire and uneasy to get in emergency situations); is available at all times to operations for lifting construction loads up to its capacity and placing them where required. Thus, it complements the basic lifting system of the two trolleys at no extra charge; and assists in lifting scaffolding for beams together with principal lifting equipment of the crane.
In the case of the SP2000A crane (intended capacity 200 to 500 tonnes - principally aimed at small yards having a dual role there). Equally suitable for a secondary role in large shipyards or for tasks completely outside the shipbuilding sector.)
To dispense with the service crane altogether. Three reasons for that are:
- The SP2000A crane is generally much lower than its big brother, it is convenient to use hired telescopic cranes for maintenance. Due to lower height of the serviced crane and lower mass of loads to be expected, capacity of the telescopic crane can be lower too; hence less cost and easier availability for hire.
- No scaffolding for maintenance of (most of) the beam and trolleys is required, as all work can be performed from the returning trolley
- Low capacity of the returning trolley makes it highly flexible and cheaper to employ for smaller construction loads.
Finally, the much debated topic of the usefulness of four points load suspension. While this is not the place to reopen this debate, it should be of interest to those favouring this way of suspension to learn that the SP2000A crane provides this possibility.
What is unusual about the arrangement is that it is based on two trolleys including the returning mode of trolley operation. For those interested in it there is no need for any confusion stemming from the announced lower capacity and lifting height of the SP2000A crane. Cranes of the same capacity and lifting height as SP2000 can be built along the concept lines of SP2000A, but they will not enjoy many of the advantages of the SP2000 concept. Whether the four points’ of suspension that the SP2000A provides is worth of so many sacrifices is up to the relevant client to decide.
Only development and construction of the SP2000 and SP2000A cranes shall fully demonstrate their superiority over the first generation systems. Inevitably, during and after that time innovation and further refinements shall continue in a never-ending process of evolution. That, under all circumstances, shall be the duty and durable commitment of those participating in this project.
Acknowledgement: the author wishes to express his thanks to Assoc. Prof. N. Tsouvalis of the National Technical University of Athens, School of Naval Architecture & Marine Engineering, for contributing to quality of the text by its review.
1. Krupp Kranbau Wilhelmshaven / Giant Gantry Cranes
2. PCT publication n° WO 2009 / 125127A1
3. V. Nevsimal – Weidenhoffer / N. Tsouvalis / V. I. Papazoglou: Goliath Gantry Cranes Their Steel Structure – A Neglected Element. (http://users.ntua.gr/tsouv/Goliath_Gantry_Cranes/)
4. V. Nevsimal – Weidenhoffer / Goliath Gantry Cranes – Extension of operational life of the structure (http://users.ntua.gr/tsouv/Goliath_Gantry_Cranes_Life_Extension/)
5. Annexures 1 & 2