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Liebherr to present innovative RL-K 7500 subsea crane with knuckle boom
During customer days at the production plant in Rostock in January 2013 Liebherr is going to present its new subsea crane,
type RL-K 7500. With this new knuckle boom crane the company extends its range of offshore cranes and offers its customers a
convenient solution for subsea operations.
The RL-K 7500 features impressive technical figures, being able to lift up to 260 t in the air and handle loads down to a
water depth of 3,400 m. The maximum rope diameter is 100 mm, the maximum overturning moment of the crane is 75.000 kNm.
Depending on customers’ specifications, the boom configuration allows for working radii of up to 50 m.
One vital advantage of the crane’s knuckle boom is that loads can be lowered to the water surface with a short rope length
between crane boom head and water line. Furthermore, the crane is equipped with a number of state-of-the-art hydraulic,
electric and electronic features and functions, some of which were submitted for patent by Liebherr, e.g. the Active Heave
Compensation system, Pactronic and the innovative winch system.
Active Heave Compensation (AHC)
Based on sophisticated Motion Reference Units (MRUs), i.e. sensors designed in-house to recognise and predict the vessel’s
motion, the AHC system compensates this movement. In order to meet the high power demands of the AHC the innovative hydraulic
hybrid drive system Pactronic, originally developed for Liebherr mobile harbour cranes, was specially adapted for subsea
applications. Pactronic is characterized by an additional energy storage device. A hydraulic accumulator supplements the
fluid pump in delivering power to the system. It serves as a pressure storage reservoir incorporating a gas in conjunction
with a hydraulic fluid. Energy is stored in this compressed gas to be released upon demand.
The revolutionary AHC system is fully integrated in the proven Litronic system. One of its most important features is its
self-learning function. It automatically recognises the vessel’s motion and adjusts itself according to this information.
Hence, the system does not need to be manually adjusted and is independent of weather conditions.
Up to 70 % of the power required to operate the AHC system is currently obtained from Pactronic. This means that the hybrid
drive system provides a maximum power of almost 4 MW.
Prior to its first delivery all functions of the AHC system were tested and optimised on a specially developed test stand at
Liebherr-Werk Nenzing. In doing so, potential risks of the system were reduced, thus lowering the costs.
Innovative winch technology
In order to ensure optimised rope guidance, the crane has a patented horizontal winch shifting system. It guarantees the
ideal fleet angle of the rope under all load conditions in both hoisting and lowering operations.
A further innovation is the vertical winch frame lifting system, which is also patented. Two hydraulic cylinders allow for
the adjustment of the lifting height without moving the drum of the hoisting winch. Due to this innovative design of the
winch unit, which is based on many years of experience and profound knowledge of Liebherr crane technology, wear of the main
wire rope is minimised, thus significantly extending its service life and reducing life cycle costs.
Easy adjustment to customer requirements regarding load and water depth can be made by exchanging the lebus shells and by
adapting the width of the winch to the actual rope diameter. Consequently, the customer is not obliged to change the complete
hsting winch.
With the RL-K 7500 Liebherr offers an innovative crane concept for subsea applications. The RL-K 7500 can be rated both as
general purpose offshore crane and as heavy lift crane, being able to hoist loads weighing up to 300 t. It can thus be
installed on board drill vessels and also heavy lift vessels.
The RL-K 7500 is calculated and built according to the latest rules and regulations. The knuckle boom of the subsea crane is
designed for use in hazardous areas. Upon special customer request the crane can additionally be equipped with an Arctic
temperature package allowing for operation at temperatures down to -40 degrees Celsius.
Source: Tobias Fröhlich,
Liebherr-Werk Nenzing GmbH, 2012-12-14
www.Liebherr.com
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