Shipyard cranes are often perceived to be heavy-duty gantry cranes, and single and double boom cranes of several hundred tons capacity. However, light loads also have to be moved around large shipbuilding sites, and smaller riverside docks or repair docks have to be served. In these cases, a specialised tower crane can be a sound alternative to a purpose-built portal-slewing crane.
Indeed, the first real shipyard cranes developed in the late 19th Century showed typical tower crane design features. Moving on rail-going portals or on fixed basis, the top slewing saddle jib models were customer-built heavy cranes not showing today’s widespread modular design, but representing lifting capacities from 6t to an impressive 150t in the massive hammerhead stile version. It was not until 1908 that Maschinenfabrik Julius Wolff & Co. introduced the first series tower crane built with large-scale construction sites in mind. Although these first-generation Wolff cranes – of which more than 10,000 have been built – were not designed specially for shipyard applications, shipbuilders nonetheless installed many hundreds of them. The basic design remained in production until the late sixties, and can still be found in the shipbuilding industry.
These top-slewing luffing jib models laid the foundation for the successful MAN Wolff special-purpose modified tower cranes seen at today’s docksides.
Other major tower crane manufacturers such as Cornell, Favelle Favco, FM Gru, Liebherr Kroll, Potain, and Terex-Peiner have also produced modified tower cranes for the shipbuilding industry. In some cases, only minor change of the series tower crane design is carried out, for example using a box-shaped portal as the undercarriage. In other cases, integrated standard crane components are hardly to be found at a first view since customer-orientated design features lead to special-purpose built cranes.
In most cases, shipyards use tower cranes with the upper range of load capacity.
Bottom-slewing modular tower cranes, typical of the 1970s, are giving way to top slewing models, mainly of the saddle jib design. Sophisticated large-scale models in the 2,000-5,000mt class, mainly built by Kroll and Potain, recently entered market niches formerly dominated by miscellaneous and dockside crane manufacturers, especially in the Far East.
Tower crane veterans of the duty cycle construction industry in the 100-500mt class find a ready market in the European river shipyard industry.
While very heavy lifts must be left to purpose-built slewing or goliath cranes, the standard tower crane permanently or temporarily installed increases the productivity of a shipbuilding yard notably. The cost effectiveness of a standard tower crane is appealing. Besides relatively low running costs (because of maintenance free components and low energy consumption thanks to modern FU regulated drives), the initial costs also tend to be lower.
In terms of costs per ton of capacity, the tower crane is cheaper than other crane types. For example, series parts can be added later, or rented, keeping the initial investment relatively low. The initial investment needs to cover only short-term plans. By using system cranes, rigging configurations like jib length and tower height can be varied ‘just in time’, as the requirements arise, and support by a local distributor is generally assured, adding to the reliability of the whole crane system.
Load placing accuracy is important when fitting huge steel structures. Generally, older electrically powered tower cranes have slow hoisting and lowering speeds and the sensitivity of control is related to the number of speed steps provided by the gearbox. On the other hand, hydraulically driven modes and the new frequency-controlled drive technology in modern tower cranes allow stepless control of every crane movement. Older Ward-Leonard drives can achieve comparable performance, but are heavier, and generate more maintenance and repair costs.
Most standard tower cranes are of the saddle jib design. As a design integrated feature, the saddle jib crane achieves better work output than a luffing jib crane – in long boom configuration, they are generally more than twice as fast. On top of this, the dead weight of the luffing jib requires the installation of bigger prime movers. Especially in the flat top design, a saddle jib crane can be installed in such a way that it passes under goliath cranes or inside large wharf halls. And the shortened counter jibs supplied on a standard tower crane can cope with narrow site conditions.
The complete crane upper of a saddle jib crane can easily be shifted in one piece by a goliath crane if special lugs are installed at the tower head. Hence, saddle jib tower cranes can be relocated on large-scale shipyards with minor preparation. Smaller units can even be moved in “one-shot”, including upper crane, tower and undercarriage, by slinging the tower crane at the strengthened tower head, securing the ballast and locking the slewing part to the tower. Another means of moving the cranes is to use self-propelled platform trailers to pick up the complete crane fixed to a purpose-built portal.
However, luffing jib cranes are more suitable in restricted spaces, for example bypassing goliath cranes, or where special fitting-out duties require extreme hook height, for example to reach over tall ship superstructures. Reduced overall tower height for over-slewing obstacles also leads to more wind resistance when the boom is lowered in or placed in an out of service position. When equipped with a shortened jib, the generally steeper load radius curve of luffing cranes results in extra load capacity in the inner working range, which can only be matched by a much bigger saddle jib crane. In contrast to older models, complex maintenance and intensive reeving of the hoisting rope are no longer required for the desired horizontal load movement when luffing.
Software programs automatically control the hoisting winch of modern tower cranes in order to adjust the hook position during luffing. As a result, the load stays at the same vertical position.
Depending on whether the application is temporary or permanent, a number of different foundation solutions are available to cope with the individual site conditions, no matter which tower crane upper is selected.
For temporary applications, standard undercarriages, cross sections, or rail going undercarriages may be the best solution. For permanent applications, customer-orientated adaptation is possible by using the standard upper tower crane. Most common are rail-going portal undercarriages, which extend the working, area and need less space. The tower can be eccentrically mounted on the portal for close proximity to the dock. The number of standard bogies can be extended by bogey supports depending on the individual wheel loads accepted at the yard.
Different heights of the track are addressed by portal-leg heights. In some cases it is even possible to reuse an existing large portal of an old wharf jib crane in order to install a system tower crane upper by using a specially built support frame.
Besides the rail-going versions, fixed bases are to be found as concrete foundations like used in the construction industry or individual solutions are found like foundation plates or studs directly-welded to a steel structure. For example, pontoon-mounted solutions turn the standard tower crane into a versatile floating crane for light duty work.
The flexibility and adaptability of the Richier tower crane range led to the construction of large-scale tower cranes with up to 62t capacity and 60-70m saddle jib in the 1970s. Some of these giants, like the GT 1450 SP800, are still working. Their movable counterweight assures constant equilibrium of the moment resulting from the lifting of the load. Optional hydraulic motors permit the periodical immersion of the crane base.
In this tradition stands the Potain MDN range of shipyard cranes incorporating many standard features of the well-established mega sized construction cranes in the Potain MD series.
One typical example is the MDN 2200 built for the Samsung shipyards in Korea. In order to carry out tilting operations normally done by goliath cranes with two trolleys, the crane is equipped with two hoisting winches and two separately or automatically controlled trolleys. The main hook lifts 50t while the auxiliary lifts 25t. The 44m high crane with a 75m jib is mounted on a tubular mast resting on a 7m wide rail going undercarriage.
Over the last 30 years Kroll has supplied tower cranes for shipyard applications in many parts of the world operating under various climatic conditions.
Korean Daewoo shipbuilding company, one of the largest shipbuilders in the world (employing more than 12,000 workers), has for many years been one of Kroll Cranes’ most important customers with a population of 10 units standard saddle jib cranes K-320 delivered in 1997, seven units K-1800 delivered 1982-1999, one unit of the K-3000, installed 2002, one unit K-4000, delivered 2002, and two units giant K-5000 cranes installed 2001 and 2002.
Besides the well-known K-10000, the 5,000mt rated all new K-5000 is claimed to be the second largest tower crane of the world. With the double trolley arrangement, 120t can be lifted at 39.1m radius, while 60t can be handled at the maximum radius of 70m. The two portal-mounted K-5000 cranes often combine their impressive force for heavy tandem lifting operations. The little smaller K-4000 provide at 92m maximum outreach still a capacity of 38t, while as well 120t can be lifted to 33.3m radius. The large crane moves on a 12m wide undercarriage, spreading the force over a purpose-built 30.3m long bogey arrangement.
The K-2500 (with a maximum capacity of 50t at 50m and 40t at 60m radius) delivered to Hyundai Construction Co. Ltd for a harbour project in Libya 1981 remained the biggest Kroll tower crane at the waterfront for a decade, but there has been a upturn in capacity with the customer made models supplied in the last three years. Even some giant K-10000 cranes have found a new application in the wharf industry.
With its broad experience in tailor–made crane designs, Kroll Cranes A/S established itself in the heavy duty crane class by developing a real alternative to individual built classic shipyard jib cranes.Modified standard tower cranes can prove to be economical lifting tools for shipyards. For permanent tower crane installations in particular, modifications can be made depending on climatic conditions by using Tropical or Arctic packages provided by the manufacturers. Such packages might include air-conditioned cabins or fully enclosed electrical cabinets.
To cope with local wind conditions, stronger mast sections from a larger crane model may have to be fitted using a standard adapter frame. The surface should be painted with special protective paint to cope with the corrosive atmosphere common in shipyards.
In order to reduce the maintenance costs associated with the crane surface in permanent installations, a purpose-built tubular tower (rather than the standard lattice tower segment) can be considered.
For the driver’s comfort, extended cabins with rest rooms and personal lifts or stairways instead of access ladders are preferred.
Assistance derricks normally supplied for standard tower cranes operating on high-rise construction sites can make access easier for electric motor maintenance. The touch-screens of sophisticated construction tower cranes provide operational data that can also be useful for the shipyard operation.
Large hydraulically powered multi-purpose luffers with strong single line pull, like those manufactured by Favelle Favco and Cornell, can be easily transferred into portal or pedestal mounted wharf cranes. Adding the standard style runner to the boom and operating a second hoisting winch alongside the main hoist adds to the versatility of these cranes.