Page 44: of Marine Technology Magazine (January 2013)

Deck Machinery & Cranes RL-K 7500 Subsea Crane RL-K 7500 Subsea Crane During customer days at the produc-tion plant in Rostock in January 2013 Liebherr presented its new subsea crane, type RL-K 7500. With this new knuckle boom crane the company extends its range of offshore cranes for subsea op- erations. The RL-K 7500 is able to lift up to 260t in the air and handle loads down to a water depth of 3,400m. The maximum rope diameter is 100mm, the maximum overturning moment of the crane is 75,000kNm. Depending on cus-tomers? speci cations, the boom con-  guration allows for working radii of up to 50 m.One 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. Based on sophisticated Motion Refer- ence Units (MRUs) the Active Heave Compensation system compensates this movement. In order to meet the high power demands of the AHC the hydrau- lic hybrid drive system Pactronic, origi- nally developed for Liebherr mobile harbor cranes, was specially adapted for subsea applications. Pactronic is charac- terized by an additional energy storage device. A hydraulic accumulator supple- ments the  uid pump in delivering pow- er to the system. It serves as a pressure storage reservoir incorporating a gas in conjunction with a hydraulic  uid. En- ergy is stored in this compressed gas to be released upon demand. The AHC system is fully integrated in the Litronic system. One of its most im-portant features is its self-learning func-tion. It automatically recognizes the ves- sel?s motion and adjusts itself according to this information. Hence, the system does not need to be manually adjusted and is independent of weather condi-tions. 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. In order to ensure optimized rope guid-ance, the crane has a patented horizontal winch shifting system that guarantees the ideal  eet angle of the rope under all load conditions in both hoisting and lowering operations. A further innova- tion is the vertical winch frame lifting system, which is also patented. Two hydraulic cylinders allow for the adjust- ment of the lifting height without mov- ing the drum of the hoisting winch. Due to this design, wear of the main wire rope is minimized, intended to extend its service life and reduce life cycle costs. With the RL-K 7500 Liebherr offers an innovative crane concept for subsea ap- plications. 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. Tobias.Frö[email protected] www.Liebherr.com January/February 2013 44 MTRMTR #1 (34-49).indd 44MTR #1 (34-49).indd 441/30/2013 12:08:48 PM1/30/2013 12:08:48 PM