420t Special Handling System
The Special Handling System (SHS) is a brand new and barrier breaking concept for launch and recovery of heavy subsea modules under extreme environment and sea states. The SHS is designed by AXTech as a new platform for module handling, and the first delivery is specially designed for handling of the subsea factory modules for the Åsgard Subsea Gas Compression project. It is installed onboard the offshore installation and IMR vessel ‘North Sea Giant’ for clients Technip and Statoil.
The purpose of the SHS is to launch and recover large and heavy modules from vessel deck to sea bed in a safe, reliable and accurate way. The SHS is rated to a SWL of 420t at a sea state as high as Hs:=4,5!
The full lifting cycle is performed over the side of the vessel and the module is fully guided at all time, both when in-air and also through the splash zone. The guiding tool includes a docking mechanism and an advanced damping system.
Landing at seabed is handled by two synchronized main lift winches and two guide wire winches. All fully heave compensated. The synchronized main lift winches are sharing one wire in a two fall system with a double fall balance sheave block. This enable full redundancy in case of winch failure and the possibility to distribute wear hotspots over a large section of the wire. I.e. the wire may be transferred back and forward between the winches during AHC operation to prevent concentrated wire wear over the sheaves.
Safe handling of modules up to 420t applies extreme forces to the system and thus it is equipped with an active dampening system allowing the load to be handled in a rigid and controlled way. The docking system enables easy docking and release of modules subsea and on deck. Due to the safe and reliable docking system there’s no need for manual rigging on the top of the module. This allows a safe operation without personnel on deck during critical and demanding operational conditions. The special design of the SHS enables the vessel to pick up the modules from the quayside without need of an external crane. Collecting a module is easily done be slewing the SHS over the quay, pick up the module and slew it onto the vessel’s sea fastening arrangement.
The SHS is operated from a dedicated Control Cabin and powered by dedicated hydraulic power units. The guide wire winches are electrical with dedicated electrical power units.