The Tenix is a new multifunctional support and troop transport ship for the New Zealand Navy currently being built at Merwede Shipyards’ facilities in Hardinxveld-Giessendam.

The ship’s superstructure weighs more than 600t. Placing this to precise geometric tolerances in both the vertical and horizontal planes would normally require two cranes or floating derricks.

As Johan van Vuuren, project manager at Merwede Shipyards, explains: ““The weight of the superstructure is no problem for a single crane. It’s the volume that makes it awkward. 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 only a single floating derrick was available, so an alternative solution for hoisting and positioning the superstructure had to be found.

Enerpac’s hydraulic SyncHoist system provided the solution. The system is designed to allow the load to be manoeuvred precisely in both vertical and horizontal planes using a single crane. Furthermore, says the company, it can keep the interplay of forces under control to exclude the risk of sagging and undesirable stresses.

To position the superstructure using the SyncHoist and crane, a special hoisting frame was made. Eight lifting points were used. Four 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 outside of the superstructure to keep the entire construction 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 precisely. These four cylinders, each with a capacity of 85t, were placed in the right position before the lift so that a sort of pre-tensioning was achieved. During the lift, this 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.

Enerpac says the crane was able to use multiple lifting points to a tolerance of ±1mm thanks to its hydraulic SyncHoist system. Cost savings resulted from the use of a single floating crane.