Huisman hatches a hybrid

25 April 2014

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Huisman has launched an innovative new active heave compensated offshore crane at OTC in London, combining the benefits of rope luffers and knuckleboom cranes. The new series of cranes will be able to lift loads of up to 1,200t, and work at depths up to 5,000m. The first of the new rope luffing knuckleboom cranes, a 900t unit, will be installed on Subsea 7’s new vessel Seven Arctic, due to be delivered in 2016.

Huisman says the overall construction weight of the crane is kept low, whilst allowing for a high lifting capacity and large lifting 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 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. This makes the crane more reliable than hydraulically driven cranes. It also means that maintenance and operational costs are reduced.

The main hoist system can be equipped with a double fall reeve system instead of a single fall reeve system, improving the lifespan of the wire and reducing operational expenditure. 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 minimized 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.

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. 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.