Ravva - Cairn’s first development success story has been the bedrock of innovation, and the foundation of our success story in the country and the region. Ravva, which in Sanskrit and Telegu means “diamond” showcases the journey of growth that Cairn has been able to achieve in its business. Incidentally, Ravva is the only field in India to get such a unique name indicating the belief of the nation in it.

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RAVVA
Celebrating 16 Years of Technical Excellence
Single Point Mooring

2. RAVVA – Celebrating 16 years of Technical Excellence
Pioneering Development
Single Point Mooring
Single Point Mooring (SPM) is a loading buoy anchored offshore that serves as a mooring and
interconnection point for tankers loading or offloading gas or fluid products. SPMs are the link between the
geostatic subsea manifold connections and the tanker. They are capable of handling ships of any size,
even very large crude carriers (VLCC).
SPM allows the tanker to head into the wind, which helps minimise the weather effect. There are four
parts in the total buoying system - the body of the buoy, mooring and anchoring elements, product transfer
system and other components.
The buoy body is usually supported on static legs attached to the seabed, with a rotating part above water
level connected to the tanker. The two sections are linked by a roller bearing, referred to as the ‘main
bearing’. The moored tanker can freely adjust itself with the winds around the buoy and find a stable
position.
The Catenary Anchor Leg Mooring (CALM) fixes the buoy to the seabed. The buoy design must account
for the behaviour of the buoy given applicable wind, wave and current conditions and tanker sizes. This
determines the optimum mooring arrangement and size of the various mooring leg components.
Anchoring points are greatly dependent on the local soil conditions. A tanker is moored to a buoy by
means of a hawser arrangement. Oil Companies International Marine Forum (OCIMF) standards are used
for designing mooring systems.
The hawser arrangement is made of a nylon rope,
which is shackled to an integrated mooring uni-joint
on the buoy deck. At the tanker end of the hawser, a
chafe chain is connected to prevent damage from the
tanker fairlead.
Hawser systems use either one or two ropes
depending on the largest size of vessel which would
be moored to the buoy. The ropes would either be
single leg or grommet leg type ropes. These are
usually connected to an OCIMF approved chafe
chain on the export tanker side and then held in the
chain stopper on board the export tanker.
The heart of each buoy is the product transfer system. From a geostatic location, e.g. a pipeline end
manifold (PLEM) which is located on the seabed, this system transfers products to the offtake tanker.
PLEM is provided near SPM with 2X20” valve connected to a 16” valve The main deliverables of the
product transfer function are:
 Direct flow from loading line to the under buoy hose of SPM during loading operation
 Bypass flow during recycle operation
 Allow pigging of pipelines
 Permit flushing of the under buoy hose and allow maintenance of the loading system by isolating
at the PLEM
The basic product transfer system components are flexible subsea hoses, generally referred to as
‘Risers’, floating hose string(s), product swivels, valves, piping, and turn table. The risers are flexible
hoses and connect the subsea piping to the buoy. The product swivel is the connection between the
piping in the geostatic parts and the rotating parts of the buoy. Product swivels range in size depending on
the size of the attached piping and the risers. Product
swivels provide one or several independent paths for fluids, gases, electrical signals or power. Swivels
are equipped with a multiple seal arrangement to minimise the possibility of leakage of the product into
the environment. Floating hose string(s) connect the buoy to the offloading tanker. The hose string can be
equipped with a breakaway coupling to prevent rupture of hoses and subsequent oil spills.

3. RAVVA – Celebrating 16 years of Technical Excellence
Pioneering Development
Other components of SPMs are:
• Boat landing, providing access to the buoy deck
• Fendering to protect the buoy
• Lifting and handling equipment to aid materials handling
• Navigational aids for maritime visibility
• An electrical subsystem to enable valve operation and to power navigation aids or other equipment