The marine systems in the Sevan units are in general based on conventional technology used onboard any ship (e.g. an oil tanker), FPSO, or drilling unit. However, the cylindrical shaped platform offers advantages compared to a ship shaped or column stabilized unit.

With the pump room located in a shaft in the middle of the unit, the amount of piping required for cargo and ballast handling is significantly reduced compared to a ship shaped unit.

The design development of the marine systems has focused on incorporating the experiences obtained from years of operating FPSO’s in the North Sea. One example is the introduction of a hydrocarbon blanketing system (HC blanketing) as standard on the Sevan FPSOs. The HC blanketing system uses hydrocarbon gas from the process plant to inert the cargo tanks as opposed to using inert gas from an inert gas generator. Th HC blanketing makes the cargo system a fully closed system with no emissions to the atmosphere. All VOC release is routed back into the gas handling system in the process plant. FPSO  Hummingbird Spirit is the first FPSO on the UK Shelf fitted with a HC blanketing system.