Configured as a crane the Mammoet Sliding Gantry, MSG-50, can lift 3,600t and has a load moment of around 70,000tm. However, being a modular system based on strand-jacking, it can be re-engineered to suit a variety of applications, as shown in a recent collaboration with Montalev in Brest, France.
Montalev’s contract culminated in a 6,700t lift of the upper deck section of the second of two new Sedco Forex oil platforms in July. One of Mammoet’s two MSG-50s was set up as eight individual lifting towers, each with two strand jacks. A bridge beam spanned two of the towers.
Having raised the main box or decks by 30m, the dock was flooded to allow the lower catamaran hull section to float and be winched in to position underneath the main box. DCN Brest, in charge of construction of the platforms, used Montalev for the heavy lifting and handling work. Total weight of each rig was nearly 16,000t, divided almost equally between the upper bridge and derrick sections, and the catamarans. Another 4,000t was later added to this in the form of fluids, fuel, drilling pipes and such like. Standing 110m high overall, the platforms are 106.5m long and 70m wide.
Components for the operation included hydraulic skid shoes, 600t and 900t capacity strand jacks and the structural steel masts. Six of these masts, each 45m long, were each mounted with two of the 900t strand jacks. The remaining two masts were part of the 50m high, 75m span gantry crane mounted with two 600t strand jacks. These gave a lifting capacity of 800t. Located on the seaward side of the dock, the gantry allowed the catamaran for each rig to be introduced without obstruction. A computerised system, run by two operators, was used to control the 14 strand jacks.
