CRANES: Huisman delivers world’s largest Leg Encircling Crane

Huisman recently delivered the cranes for the Seajacks Scylla, the new build wind turbine installation vessel for Seajacks UK Ltd. This jack up vessel is currently nearing completion at the yard of Samsung Heavy Industries in South Korea. The Seajacks Scylla, based on the Gusto MSC NG14000X design, has been specifically designed to meet the demands associated with working UK Round 3, Scottish territorial waters and the other North West European markets. The vessel will be the fifth new self-propelled jack-up to join the Seajacks fleet since 2009.

With a capacity of 1,500mt at 34m, the main crane of the “Seajacks Scylla” is the world’s largest leg encircling crane. An exceptional detaill for this type of crane is that it is installed around the starboard-aft jack up leg of the vessel. The crane has an internal leg opening of 11m diameter to ensure free travel of the leg through the crane. This solution saves significant amount of deck space on the vessel.

Crane features

The crane is equipped with three different hoist systems. The main hoist has a capacity of 1,500mt SWL, which is suitable for installation of turbine foundations and monopiles. Nacelles and towers up to 600mt can be lifted with the secondary hoist. For a fast installation of lighter loads, e.g. wind turbine blades, a third, high speed, hoist system with 100mt capacity is installed.

To reach high lifting heights, the crane is equipped with lattice type boom of 110m long. It is a ‘parallel’ boom type, which can be stored around the forward jack up leg of the vessel. This way the boom takes up less deck space during storage. When the crane is needed, the boom can be hoisted over the forward leg, even when this is fully retracted e.g. in transit.

Slew bearing

The leg encircling crane is mounted on a 14m diameter segmented slew bearing. This bearing is completely developed and manufactured in house by Huisman. Application of a slew bearing is advantageous over traditional slew mechanisms (e.g. bogie systems or wheels). Because of the local load transfer and a better distribution of the loads the weight of the slew mechanism can be significantly reduced. Weight is an important factor for vessels, and especially for jack up units. Lower weights result in a higher vessel payload and less loading on the vessel jacking system. This makes the slew bearing a valuable feature of the Huisman leg encircling crane.

The raceways and rollers of the bearing are protected from the harsh marine environment by the completely enclosed construction which is filled with grease. Therefore the amount of maintenance on the slew bearing is limited. If maintenance is required, special hatches are installed to reach the inside of the enclosed construction. Through these hatches the rollers and cages can be inspected or exchanged. If needed, segments can be dismantled to exchange complete raceways. This allows inspection, maintenance, and possibly replacement of the complete bearing segments if needed without dismounting the complete bearing.

Weight optimization

To reduce the weight even further, the crane is constructed out of high tensile steel where possible. This has a higher load bearing capacity and therefore allows for a lighter construction. The complete crane is modelled in a computer program for detailed finite element calculations. All excess steel has thereby been omitted.

Electric drive system

All movements of the crane are electrically driven by means of variable frequency drives. Electric drive systems give a high level of control and accuracy and it is more environmental friendly than hydraulic drive systems. Hydraulic drive systems have an increased risk of oil leakages into the environment. In addition, electric  drive systems are more efficient and do not require power during standstill. Therefore this system uses less energy.

The electric power supplies and control signals are transferred from the vessel to the crane via a 14m diameter slip ring. This slip ring is mounted on the bottom of the crane. The use of a slip ring instead of a drag chain allows the crane to revolve limitlessly around its axis.

Turnkey delivery

The complete development of the crane, from first design to final assembly, is done in house by Huisman. In the crane only components from renowned Western European suppliers have been used. The design has been made in the Huisman head office in Schiedam, the manufacturing has been performed at the Huisman facility in the P.R. of China.

Maarten van de Waal, Sales Engineer Cranes, says: “The house of the crane has been fully assembled in our workshop. This makes it possible to test most crane functions before delivery of the crane. After factory testing of different components, the crane has been transported to the shipyard in two pieces: the slew section with back frame and the boom. Here it is installed onboard the vessel.” At the moment of writing, commissioning of the crane is nearing completion. After this, the final load tests need to be performed and the crane can be put in operation. For its first project, the crane will used to install XL monopiles exceeding 1,500mt in weight at the Veja Mate wind farm.