Alternative drive systems for offshore operations

25th May 2018

Alternative drive systems for offshore operations

GROUNDED OFFSHORE Pedestal-mounted lattice boom cranes with an innovative electric drive concept

Owing to increasing safety requirements and more stringent environmental regulations, use of electric drive technology has become the subject of ever stronger debate in the offshore sector.

Its higher precision and better dynamics and efficiency are winning over more and more users on the high seas. In cooperation with industrial gearbox and geared motors supplier

Bonfiglioli, offshore pedestal- mounted lattice boom cranes, with an innovative electric drive concept, have been commissioned by crane manufacturer Palfinger Marine.

For steel lattice boom cranes with a reach of up to 57 m and a safe working load of 60 t, 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. After calculating the necessary torques and motor outputs, it became clear that a simple electrical drive could not meet the requirements needed 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.
Owing to the tight installation space requiring a specific layout and 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 t. The boom winch has two size IEC 315 motors, each weighing 1.7 t. 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 was there supposed to be consideration of transmission of drive power, but also the size and weight of the motors themselves. At about 2 m long and with the aforementioned heavy weight for every engine, the special asynchronous motors are an important factor. Concerning the drive’s load distribution, which is handled by electronic control, mechanical elements must also be safely arranged.

The mechanical solution from Bonfiglioli 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 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 2 m 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.

The specially designed drive components were implemented by engineers from Bonfiglioli, who have in-depth expertise and decades of experience in drive technology. In close cooperation with machinery manufacturers, it develops and designs machine-specific solutions in a short space of time. After a thorough range of tests tailored to specific application requirements, the product goes into serial production, ensuring reliable supply to customers.