Huisman introduces rope luffing knuckle boom crane

The patented active heave-compensated (AHC) crane, Huisman noted, provides unparalleled performance by combining the benefits of a traditional rope luffing crane and a knuckle boom crane. As such, it offers a high lifting height and a large capacity at outreach. The capacities of the new cranes range from 400 up to 1,200 tonnes. They can be deployed for water depths up to 5,000m. The first crane of this type, a 900-tonne rope luffing knuckle boom crane for Subsea 7’s Seven Arctic, is scheduled for delivery in 2016.
For the innovative and patented design proven key components are used, Huisman said. According to the global specialist in lifting, drilling, and subsea solutions the overall construction weight of the crane can be kept low, while allowing a high lifting capacity and large radius. By incorporating a knuckle in the design of the crane, it is possible to reduce the pendulum of the hook and, if extended, it can allow for high lifting heights, the company noted. Furthermore, the boom of the crane can be stored vertically saving valuable deck space. The main hoisting system comprises a traction and storage winch system and a separate heave compensation system. This means both lifting/lowering and heave compensation can occur simultaneously with no performance interdependency, resulting in a better overall system performance and increased safety. A failure in main hoisting system will not affect the heave compensator or the other way around.
Because the crane is fully electrically driven, the power consumption, noise levels, and the number of components are reduced. Maintenance and operational costs are also cut down. The main hoist system can be equipped with a double fall reeve system instead of a single fall reeve system, improving the life span of the wire and therewith reducing operational expenditure. Further the lifetime of the wire rope is significantly extended by the combined active and passive heave compensation system on the main hoist, since the number of sheave bends is minimised and there is no drum crushing or wire rope cut-ins on the winch. The passive mode of the heave system includes built-in redundancy, so the passive system is fail-safe. During splash zone lifts, substantial reduction of the dynamic forces on the crane and the lifted object is achieved by using the passive system as a shock absorber, and can be used to avoid any resonance during subsea lifts. Furthermore, Huisman said, real-time active heave compensation can take place at a very low power consumption level. The anti-twist device prevents twisting of the lower block and wire rope during subsea lifts in double fall configuration, it added. In addition, it lowers the point of application of the wire rope, which improves the stability of the vessel and reduces the boom tip motion.