Alternative drive systems for offshore cranes by Bonfiglioli
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Alternative drive systems for offshore cranes by Bonfiglioli

Electrifying solutions

Even in the offshore sector, current technical developments show no sign of slowing. Up to now, the most common drive technology on ships and offshore platforms has been hydraulics. Due to increasing safety requirements and more stringent environmental regulations, use of electric drive technology has become the subject of ever stronger debate. Its higher precision and better dynamics and efficiency are winning over more and more users on the high seas. In cooperation with Bonfiglioli, offshore pedestal-mounted lattice boom cranes with an innovative electric drive concept have recently been commissioned by Palfinger Marine.

The mechanical demands sparked ambition in the engineers. For steel lattice boom cranes with a reach of up to 57 meters and a safe working load of 60 tons, the aim was to develop the most compact electric drives possible for the main winch and boom winch. The steel lattice structure of the crane boom strictly dictated installation space, because, for safety reasons, nothing can protrude beyond the lattice structure. At the same time, the size of the crane also dictated the cable thicknesses and lengths, and the dimensions of the drum. Figure in the necessary torques and motor outputs, and it quickly became clear that a simple electrical drive could not meet the perform adequately within the available space. The design task was therefore to distribute the power to several motors while transferring the total torque to the winch drum.

Tight installation space requires a specific layout

Based on calculations within the given conditions, the drive for the rope winch that operates the hook was divided among four size IEC 280 electric motors, each weighing about 1.2 tons. The boom winch has size IEC 315 two motors, each weighing in at 1.7 tons. This took care of the entrance side, but there was still another design task to tackle: the effective layout and connection of the motors to the winch system. Not only transmission of drive power had to be considered, but also the size and weight of the motors themselves. At about two meters long and with the aforementioned heavy weight per engine, the special asynchronous motors are an important factor. When it comes to the drive’s load distribution, which is handled by electronic control, then the purely mechanical elements must also be safely arranged.

The mechanical solution from Bonfiglioli O&K Antriebstechnik consists of two components, each on both sides of the drum: a motor flange and an angle system flowing into the actual winch system. For the boom winch, the angle gear is designed to have a fail-safe brake mounted opposite the engine power side for emergency situations. This has significant safety implications, because the crane boom remains in position and cannot sag, even when power is interrupted. A bevel gear setup very efficiently transfers the motor input torque to the winch’s planetary gear, which is located in the winch drum. The winch itself is at the crane tower and experiences only the rotational movements of the tower. There should be no anomalies when lubricating the angular gear. A superordinate control system ensures synchronous operation of the drives on both sides of the winch.
The large cable winch drum, about two meters wide, is mounted near the tower in the boom of the crane. The four cable winch drives are also arranged on both sides of the winch drum, with two drives on each side directly facing each other. These motors are also mounted with a motor flange on an angular gear. This transfers the combined power of the two motors, which are joined at right angles to the planetary gear integrated into the winch drum. Of particular importance here is the sophisticated lubrication system for the bevel gear setup. It ensures optimal lubricant supply regardless of the boom position. The four motors are also inverter-fed and work in perfect synchronization with each other. The paint work on the drive components from Bonfiglioli O&K Antriebstechnik complies for three-layered maritime applications with the specific C5M standards according to ISO 12944 or four-layer NORSOK M-501.

Full electrification offers clear advantages

Together with the electric rotary drives, the boom crane is completely electrically driven. The control system is at the cutting edge of current technology, operates and reacts quickly and ensures safety up to a wave height of up to six meters, which can only be reached during stormy winds. Another advantage of the electrical drives is that optimized load diagrams ensure flexibility in operation and even enable remote access to the crane. This can be implemented for fault detection and fast support, for example. In addition, the system largely uses standard components, which eases maintenance and speeds delivery of replacement parts. All in all, the electric drives provide greater energy efficiency, thus ensuring lower energy consumption and practically eliminating the risk of oil contamination that may occur from a breakdown or accident involving the hydraulic system.

The electric drives have proven completely effective for decades in other industries that operate in harsh environmental conditions. In construction machinery, they can serve just as reliably as travel or slewing drives as in wind turbines — around the globe and under extreme weather conditions. Developed to strict EN13852-1 and NORSOK R002 standards, they reliably meet all requirements, even in offshore applications. Cranes equipped with electric drive technology have fewer wear-prone components, which means lower maintenance costs. Above all, they work much more quietly and produce noticeably less vibration. So there are many reasons to implement this change.

Expertise and experience are fundamental

The specially designed drive components were implemented by engineers from Bonfiglioli O&K Antriebstechnik, who have in-depth expertise and decades of experience in drive technology. In close cooperation with machinery manufacturers, they develop and design machine-specific solutions in an amazingly short time. After a thorough range of tests tailored to specific application requirements, the product will go into serial production, ensuring reliable supply to customers.