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are maintenance free, and the central access
shaft and external structure can be inspected
without the need to shut down production.
A series of high-integrity connectors connect the buoy to the FPSO’s turret, with each
connector designed to handle a vertical load of
around 1,200 metric tons ( 1,323 tons) – capacities well above anything previously developed
by the industry, SBM claims. To mate the buoy
to the turret, both for the initial installation
and for subsequent reconnections, the company developed a novel heave compensation
system which is built into the turret. Without
the heave compensator, the two-body system
(buoy and FPSO connected by a pull-in line)
would undergo a resonant mode correspond-
ing to typical wave frequencies.
The buoy’s underside is attached to three
sets of mooring lines. Each mooring line incorporates a spring buoy connected to the
disconnectable buoy by 120 m (393 ft) of chain.
Below the spring buoy the mooring line is
composed of chain-polyester-chain sections,
with the polyester being in three segments
of 1,200 mm length. The attachment arrangement, and the fact that the buoy remains under
water and is normally located within the vessel, would have made it difficult to access the
mooring lines to adjust tension.
In response, SBM developed and quali-
fied an In-Line Mooring Connector (ILMC),
a tensioning device situated within the chain
section of each mooring line a few hundred
meters from the buoy. The ILMC incorporates
a turning sheave and a ratchet, which allows
an anchor handling vessel to pull-in additional
length of line on the fully installed mooring
system to achieve the initial pre-tension re-
quired and to later compensate for any stretch
in the polyester legs that may occur over the
life of the TMS. This solution, the company
claims, could allow future turret/buoy FPSOs
to be installed in even deeper water.
In the case of severe weather like a hurri-
cane, the Turritella is designed to safely shut
in production operations, disconnect, and sail
away. Once the danger has passed, allowing
production to be reinstated, reconnection
should take around 24 hours including time
spent inspecting the buoy and the moorings.
In its connected condition (FPSO hooked up
to buoy), the system is designed to withstand
a 10,000-year winter storm. The buoy/riser/
mooring system without the FPSO hooked up
is engineered to withstand a 100-year hurricane. The wave height anticipated in the 10,000-
year winter storm is around 72% of the wave
height associated with the 100-year hurricane.
Following this initial application, SBM is
looking to offer the TMS/buoy combination
elsewhere in the Gulf of Mexico and to other
severe environment areas. •
The Turritella’s large buoy has an unprecedented
displacement for an FPSO system, according to SBM.