Shuttle tankers are very complex with respect to dynamic positioning capability, bow loading cargo systems and VOC emission control systems. DNV has been an active party in the development of shuttle tankers and has gained considerable insight into and experience of construction, equipment and operations. Currently more than 60 shuttle tankers in operation, roughly 70 per cent of the world fleet, are classed by DNV. Ten more are under construction; Olav Tveit writes:
Converted at Haugesund Mekaniske Verksted in 1980, Anders Wilhelmsen’s WILNORA became DNV’s first shuttle tanker with side thrusters fore and aft, vari- able pitch main propellers, bow loading, single point mooring equipment and a forward navigation bridge. As the shuttle tanker demand in the North Sea grew, DNV launched its first Dynamic Position- ing Systems (DYNPOS) rules in 1977, rules for Tanker Bow Loading systems in 1985, and rule requirements for STL (Sub- merged Turret Loading) in 1995. Today dynamically positioned shuttle tankers are common.
The permit regime for reducing emissions of non-methane volatile organic compounds (NMVOC) was implemented in the Norwegian North Sea sector in 2000. Operators were required to reduce but also address structural fatigue life. For vessels operating in harsh environments, like many shuttle tankers, owners may specify standards beyond those required by the CSR.
NMVOC emissions by 78 per cent, with an operational vapour recovery regularity of 95 per cent. By 2005, 95 per cent of all crude oil had to be loaded onto vessels with VOC recovery systems. Rapid technol- ogy development and concept testing on board DNV-classed ships led to DNV’s class notation VCS-3 in 2000.
High installation and operation costs, significant power requirements and regularity problems gave rise to a search for alternatives. In 2002, Knutsen OAS Shipping developed its passive KVOC system for loading, with DNV as its concept verification, testing and installation partner. The North Sea operators’ VOC industry partnership (VOCIC) estimates that KVOC, combined with increased tank pressure and small swirl absorption systems, reduces emissions by 50–70 per cent with 100 per cent regularity. In 2010, the legislation was changed by imple- menting a technology-neutral maximum emission limit of 0.45 kg NMVOC per ton loaded crude oil per offshore loading point.