Merwede Shipyard positioned superstructure using SyncHoist Instead of the usual two floating cranes, only a single one was available for placing the superstructure – weighing over 600 tons – onto a Multi Role Vessel under construction for the New Zealand Ministry of Defence at Merwede Shipyard. Merwede Shipyards was looking for an alternative; calling Enerpac in was the answer. The result was a perfect combination of a single floating crane plus Enerpac's hydraulic SyncHoist positioning system.

Merwede Shipyard is one of the leading shipyards in the Netherlands and part of the IHC Holland Merwede BV group of companies. The 'MRV' is currently being built at their facilities in Hardinxveld-Giessendam as an order for the Australian company Tenix Defence Pty. Ltd who is the prime contractor for delivery of a fleet of 7 vessels to the New Zealand MOD. The MRV is a new multifunctional transport and patrol vessel for the Royal New Zealand Navy. The ship is constructed at Merwede Shipyard however the superstructure and the funnel unit were outsourced to Maatschappij De Maas BV in Rotterdam, which operates from the former RDM premises on Heijplaat. This is also where the superstructure and the funnel unit had to be placed on the ship that was towed to Maatschappij De Maas after being launched at Merwede Shipyard.

A single crane plus SyncHoist

This kind of placement task for heavy ship components – the superstructure of the MRV weighs over 600 tons – to precise geometric tolerances in both the vertical and horizontal planes normally requires two cranes or floating derricks to be used. The problem is that the construction is made of sheet steel and care has to be taken that all parts of the construction are moved synchronously when it is lifted, otherwise unacceptable stresses can arise within the construction. "The weight of the superstructure is no problem for a single crane. It's the volume that makes it awkward," explains Johan van Vuuren, production manager at Merwede Shipyard. "You could compare it to lifting a flexible cardboard box. That's why we designed the construction for hoisting using two cranes." However, in this case there was only a single floating derrick available, so an alternative solution had to be found for hoisting and positioning the superstructure. Enerpac's tried and tested hydraulic system SyncHoist provided the solution. The SyncHoist system was developed by Enerpac to improve the accuracy of the placement. It allows the load to be manoeuvred precisely in the vertical and horizontal plane using just a single crane. Furthermore, it can keep the interplay of forces under tight control so that the risk of sagging and the consequent undesirable stresses can be excluded.

Eight lifting points To be able to position the superstructure using the combination of SyncHoist plus a single crane, a special hoisting frame was made. As Johan van Vuuren explained, "Using this lifting frame, you see, we were able to keep all the features that we had constructed intact." A total of eight lifting points were used. Four of these were provided on two heavy-duty beams on the underside of the superstructure, with lifting cables that ran through the construction. The other four cables were attached to the very outside of the superstructure and were there to keep the entire construction properly balanced. The double-action hydraulic (lifting) cylinders of the SyncHoist system were integrated into the four outermost cables. The double action allows both lifting and lowering corrections in each cable to be controlled extremely precisely. These four cylinders, each with a capacity of 85 tons, were placed in the right position before the lift, so that a sort of pre-tensioning was achieved. During the lift, this pre-tensioning ensured that the entire superstructure could be hoisted synchronously. Then, while lifting and positioning the superstructure, the interplay of forces in the cylinders and the movements are monitored by sensors and a PLC control system, and corrected if necessary to the pre-defined values.

Major advantages

Using the SyncHoist system provided significant advantages for Merwede Shipyard. Thanks to Enerpac's hydraulic SyncHoist system, the crane was able to use multiple lifting points to a tolerance of ±1mm. Not only were there cost savings due to the fact that just a single floating crane was used, but Enerpac was also able to guarantee that the superstructure could be positioned without being subject to stresses. Although this did not really play a part since there was relatively little wind, the SyncHoist system is less affected by weather conditions than the application involving two cranes.