Over the past years Heerema Marine Contractors (HMC) has developed the QUAD lift method enabling the lift of single piece objects up to 30,000mT. This development is driven by the demand from our clients to install or remove larger topsides, both in size and weight. Lifting with two (or more) vessels simultaneously has been done before. Unique is that the QUAD lift operation is performed on DP. Two vessels lifting the topsides from opposite sides, instead of lifting the topsides from one side, creates the possibility for increasing dimensions and layouts of the topsides.
The connection of the two crane vessels to the lifted object means that all actions taken on one ship influences not only the lifted object but also the second crane vessel. This requires a clear communication plan and full understanding of the complete system such as the DP behaviour, stability, ballast operations and crane operations. During a QUAD lift operation the Dynamic Positioning (DP) system plays an important role. Therefore in the development process the DP-system was modified to ensure stability of the DP system throughout the entire operation. A systematic series of tests was performed to gain insight in the DP behaviour of both vessels with the goal to ensure a synchronous move with two vessels connected in a QUAD lift configuration.
In 2018 a demonstration QUAD lift is performed using Balder and Thialf to show HMCs commitment to perform this kind of operations in the future. The QUAD lift demonstration lift was prepared and executed in the Heerema Simulation Center (HSC) with the offshore crew in preparation of the actual offshore execution.
This paper will address the steps followed to prepare for the offshore execution, describing DP behaviour, vessel coupled dynamics and human factor aspects. Based on the offshore experience validation was performed on the numerical tools used in the preparation.