Vessel Adapted for Multiple Installation and Salvage

Abstract

For offshore developments, the installation of production decks onto floaters (e.g. spars for deep water developments) or fixed platforms using a heavy lift derrick barge is now well established, though, for high payloads, this requires multiple lifts and hence extensive offshore hook-up. As demand for lift vessels increases, their availability to match a specific project’s schedule cannot be guaranteed. Consequently, an alternative deck installation vessel design has been developed for not only installing decks onto floaters, but also onto high air gap (circa 20 m) fixed platforms. This paper will present this new design. The new vessel design consists of a linked catamaran shaped vessel with dimensions that permit it to go around the floater hull or jacket so that the deck can be lowered and stabbed. The procedure for lowering is based on motorized “legs” to achieve a rapid weight transfer in severe sea-states and also permits the deck to be raised up once at site to achieve a high air gap installation on a fixed substructure. This new vessel design greatly extends the geographical range for deck installation using the float-over method and offers a cost effective alternative to relying on crane vessels for installation. Additionally, the vessel can perform a range of other tasks, particularly relating to decommissioning of facilities, or offshore wind-farm turbine installation.