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APPENDIX 4
Single Point Mooring Guidelines
1 INTRODUCTION
1.1 This Appendix outlines general information to supplement that given in
Section 3.14 of TERMPOL Surveys and Studies. It should not be regarded as
exhaustive. The proponent’s attention is drawn to other standards,
recommendations or guidelines of various international authorities or
associations such as those produced by the Oil Companies International
Marine Forum (OCIMF).
2 DIMENSIONS
2.1 The mooring circle should have a minimum radius of three times (3X) the
length of the design ship. A larger radius may be required depending on the
local weather and sea conditions.
2.2 The mooring circle should be so located that the closest point on its
circumference should be not less than 300 meters from the requisite minimum
water depth contour.
3 CONSTRUCTION
3.1 Swivels should be operable in all weather including icing conditions and
should be designed so that the turntable can rotate freely with the floating
hose assembly under the wind and current forces. Seals should prevent all
leakage and should be effective in all weather conditions that are within
the operating criteria.
3.2 Each SPM should be equipped with a mooring load monitoring device.
3.3 An SPM buoy should be designed for "fail-safe" buoyancy provided
by compartmentation, double-bottom tanks, mono-cellular flotation or other
means. Adverse effects of ice accretion on buoyancy and stability should be
investigated.
3.4 The buoy should be fitted with integral fendering and a skirt for
protection against override by ships and impact with the floating hoses. The
fendering system should be such that it not only protects against collision
by ships at drift speeds, but is also capable of absorbing any impact should
the fenders come into contact with any part of the cargo system.
3.5 The buoy should be designed so that when the maximum mooring load is
applied statically to the installed buoy in calm water, no part of the deck
will be submerged.
3.6 The construction of the buoy body, rotating assembly, mooring fittings and
bearings should be such that the maximum mooring force can be transmitted to
the buoy anchor system, but the system should be designed such that the
ship-to-buoy mooring will fail before overloading the buoy or its anchorage
system.
3.7 Automatically activated lights and foghorns, fire alarms and fire
extinguishers should be provided for buoy structures and should comply with
CCG standards. This equipment should also include at least one lifebuoy with
attached, automatic light and buoyant life lines. Means should also be
provided for the attachment of safety lines in all working areas and
gratings. Ladders and handrails should be fitted as required to ensure safe
access to operating equipment. All electrical equipment should be
explosion-proof and watertight.
4 LINES
4.1 The sea bed manifold of the submarine lines should be anchored to the sea
bottom, and should be provided with a "failsafe", automatic means
of closure which can also be activated manually at the buoy or at a shore
connection.
4.2 Subject to an acceptable inspection and maintenance program, all submarine
lines should be entrenched in the sea bottom, where the following measures
cannot be met:
- a special study should be carried out to ensure that the lines will not
form an obstruction to natural sediment movement;
- the lines should traverse a route of minimum cross current and uniform
gradient and there should be no unsupported sections; and
- anchors and/or concrete weight jacks may be required to stabilize the
lines against sliding.
4.3 Floating hoses should be connected to the buoy piping in such a manner to
ensure that loads on the hoses are kept within the manufacturer’s design
limits. Special consideration should be given to the effect of icing on the
hose buoyancy.
4.4 Under-buoy hoses should be designed so that under all conditions they form
a faired curve between the bottom manifold and the underside of the buoy and
do not touch bottom. Under-buoy hoses should have electrical discontinuity.
All hoses and ancillary equipment, including flange bolting and gaskets
should comply with the "Buoy Mooring Forum Hose Guide", published
by the OCIMF.
4.5 The maximum mooring line load in any ship-to-buoy line should be limited
to forty percent (40%) of the breaking strength of the line. This
ship-to-buoy mooring line should be designed as the weakest link in the
system. Compatible automatic sealing breakaway type couplings should be
fitted in the hose lines.
5 ANCHORING
5.1 An 6-leg anchor system or an alternative acceptable anchoring system
should be provided for the buoy. The anchorage system should have adequate
strength to maintain buoy stability in the event of failure of any one part
without damage to the under-buoy hoses or remaining chains.
5.2 All anchor chains should have sufficient length so that under maximum
mooring load a sufficient length of chain at the anchor end will remain in
contact with the sea-bed.
5.3 The maximum design tension in any anchor chain should not exceed
thirty-five percent (35%) of its breaking strength.
6 OPERATION
6.1 The cessation of cargo transfer operations and/or the tanker departure
from a SPM prior to adverse weather conditions is often based on specified
sea, swell, and wind conditions. These specifications are site-specific,
however, the following are averages of world wide data assessments and are
provided for general information:
- cargo transfer operations should be suspended at an SPM when wave height
are in excess of 2.5 meters significant and/or wind velocities exceed
20m/s (39 knots);
- tankers should disengage from the SPM when seas with wave heights exceed
4 meters significant and/or wind velocities exceed 30 m/s (58 knots); and
- loading tanks attached to the buoy should have adequate stability and
sea-keeping characteristics and compatible hose securing devices.
6.2 In the interest of safety, a consistent site-specific weather forecasting
service is recommended for SPM locations.
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