Section
16 Long-term nearshore positional mooring system
16.1 General
16.1.1 The requirements of this Section shall apply to inshore/at-shore-moored units with
station-keeping capabilities to remain at terminal facilities and are additional to
those applicable in other Sections of the Rules. This shall cover units with
permanent or semi-permanent mooring systems at terminal facilities such as floating
power generation, LNG terminals with onshore regasification or a FSRU that
regasifies cargo LNG and exports to a gas network onshore. Essentially, this Section
does not apply to a ‘mooring system’ anchored to the sea bed.
16.1.2 The terminal mooring system is to provide restraining forces at terminal facilities
in the long term, normally within the entire duration of service life of units which
are not required to leave the berth during unfavourable weather conditions, unless
it is planned to do so. This will suggest mooring systems at the following
inshore/at-shore facilities (where units' offloading manifolds are often connected
to a distribution facility onshore through marine loading arms or flexible
hoses):
- Jetty, which is a structure providing berths at some
distance from the shore. A jetty may be connected to the shore by a
causeway, or may be of the island type.
- Quay, which is a berth structure backing on to the shore
or reclaimed land.
- Dolphin, which is an isolated structure or strongpoint
to facilitate holding a unit in position at its berth; with bollards or
hooks for securing the unit and for preventing it from moving away from a
berth due to combined wave, wind and current action.
16.1.3 The jetty/pier layout and mooring equipment arrangement and
specifications, in addition to the plans and data listed in Pt 3, Ch 10, 1.4 Plans and data submission,
will be subject to review and approval. The information and plans are to be
submitted in an agreed electronic format, to cover the design review and class
approval of the long-term nearshore positional mooring system.
16.2 Environment condition
16.2.1 The extreme environmental conditions applicable to the location or
operating areas are to be specified, together with all operating environmental
limits. Detailed specialist environmental reports are to be submitted, with
sufficient supporting information to demonstrate the validity of the limiting
criteria. See
Pt 3, Ch 10, 3 Environmental conditions for
more details.
16.2.2 Wave headings of all the possible direction should be considered unless limited
heading angles are defined in the specialist environmental report.
16.2.3 Sea bed bathymetry may vary considerably around the units in case they are moored
near the shoreline. Such a change in bathymetry may affect waves and currents. The
current load can be even higher in the under-keel clearance. This should be
investigated in the environmental specialist report and considered for the
analysis.
16.2.4 A tsunami can have significant effects on the units. The specialist environmental
report should include the likelihood of a tsunami and its effect, if applicable.
16.2.6 For permanent inshore/at-shore-moored units operating in protected waters such as
harbours or inland lakes, or semi-permanent units where such units need not remain
at shore in adverse weather conditions, the design environmental return periods
could be less as agreed with LR and shall be considered as a design limitation of
the units.
16.2.7 When a unit is disconnectable and is expected to operate near other structures,
return period should be at least 10 years. This is applicable, for instance, to a
FSRU operating near other structures operating at another jetty in the same
harbour.
16.2.8 For semi-permanent units, disconnection procedures from terminal facilities such as
marine loading arms or flexible hoses are to be included in the operation manual
submitted for approval. The manual at the minimum should contain:
- Environment parameter threshold to disconnect;
- Actions at incremental environment towards threshold value
to disconnect (e.g. actions at incremental wind speeds before disconnection).
16.3 Mooring layout
16.3.1 The optimum restraining force distribution in mooring layout at terminal facilities,
either inshore or at-shore, is provided by combined breast and spring lines
arrangement. Within the context of this sub-Section:
- Breast lines are mooring lines orientated as perpendicular
as possible to the longitudinal centreline of the units and as far aft and
forward as possible.
- Spring lines are mooring lines orientated as parallel as
possible to the longitudinal centreline of the units.
16.3.2 A mooring layout plan is to be submitted for approval. The arrangement of such
combined mooring lines shall be demonstrated to be capable of:
- Maintaining excursion of units during offloading/cargo
transfer operation within allowable operating envelope of gangways and access
structures (if present), and marine loading arms or flexible hoses; as defined
by terminal facilities administrator and/or manufacturer specifications.
- Maintaining mooring load below working load limit of mooring
line and its tail component, during operation. The working load limit is to
follow Table 10.6.1 Minimum factors of safety
for anchor lines for floating offshore installations at a fixed
location. For fibre ropes, follow
Pt 3, Ch 10, 9 Fibre ropes.
- Maintaining restraining forces exerted to shipboard mooring
fittings below their respective SWL capacities.
16.4 Design considerations
16.4.1 The terminal mooring system is to be designed by considering as
applicable, requirements of Pt 3, Ch 10, 4 Design aspects, Pt 3, Ch 10, 5 Design analysis and Pt 3, Ch 10, 6 Anchor lines; this shall cover
verification on strength adequacy and fatigue life of mooring components including
applicable factors of safety and detailed design methodology. For further reference,
see the ShipRight procedure for Long-Term Nearshore Positional Mooring
System associated with this Section of the Rules.
16.4.2 The corrosion and wear should be considered for mooring system design.
16.4.3 For nearshore positional mooring system with novel features, the design
considerations and methodology should be reviewed and agreed by LR.
16.4.4 The effect of passing vessel on nearshore positional mooring system should be
considered and the loads induced by passing vessel shall be combined with relevant
environmental conditions.
16.4.5 The effects of long period waves such as infragravity waves, that could force
seiching especially in certain enclosed mooring terminal, as well as further impact
of infragravity waves which may be free or bound to sea and swell waves, should be
considered.
16.4.6 In the location where snow or ice can be accreting, the effect should be considered
in the design and analysis.
16.4.7 Sea bed bathymetry may affect waves and currents in case the floating system is
moored near the shoreline. Such an effect should be taken into account for the
design.
16.4.8 UV degradation and high temperature for the mooring lines above the water can reduce
the mooring strength and fatigue capacities especially on fibre ropes and should be
considered during the design.
16.4.9 The above water components of the mooring system especially fibre ropes are
vulnerable to fire and blast. This can particularly be an issue for jetty moored
FLNG units with large topsides processing facilities where there may be jet fire
scenarios which the mooring system should survive. This risk should be considered
during the design for accidental and post-accidental fire and blast design
conditions.
16.5 Mooring winches
16.6 Mooring fittings and components
16.6.2 The design and specification of mooring fittings shall ensure that mooring fittings
and supporting structure to which they are attached do not suffer structural damage
before the mooring line breaks.
16.7 Mooring terminal facilities
16.7.1 Safety aspects in designing mooring at terminal facilities should be put in place,
including access by emergency services, escape routes from hazardous areas and the
provision of fire-fighting equipment.
16.7.2 Although design aspects of mooring terminal facilities are excluded in this Section,
LR shall consider recognised standards and/or guidelines which provide
recommendations and initial design strategy to build, maintain and refurbish mooring
terminals. Provided that the level of safety is agreed by LR, the followings
publications could be adopted:
- BS 6349-2:2019, “Maritime works, Part 2:Code of practice
for the design of quay walls, jetties and dolphin”;
- A number of related publications by working groups under
Association for Waterborne Transport Infrastructures (PIANC), e.g. PIANC Report
153: “Recommendations for the Design and Assessment of Marine Oil and
Petrochemical Terminals”, and PIANC Report 116: “Safety Aspects affecting the
Berthing Operations of Tankers to Oil and Gas Terminals”;
- OCIMF MEG4, 4th edition 2018, Section 9.5 pertinent to quick
release hooks and bollards.
16.8 General guidelines on maintenance and inspection
16.8.1 A mooring system management plan is to be provided to record the lifecycles of
mooring equipment (e.g. mooring fittings, fairleads, mooring lines, tails, pennants,
joining shackles, etc.), including operating, maintenance and inspection
instructions as recommended by the original equipment manufacturer. Publications
from OCIMF (i.e. latest edition of Mooring Equipment Guidelines) can be adopted as
agreed with LR.
The mooring system management plan is to be approved by LR and must be
retained on board throughout the service life of the unit and be considered as live
documents for recording any changes that have occurred to the mooring system since
the unit was built or on the day the long-term near shore positional mooring system
notation was given.
16.8.2 The format of the mooring system management plan shall contain, as a minimum,
information covering the following:
- Mooring system design philosophy;
- Records of mooring system including historical data of
upgrades or modifications to mooring equipment; and
- Inspection, maintenance including record for related
documents and certifications, and retirement strategy for mooring lines based on
guidance from the original equipment manufacturer.
For chain, wire and other steel components, see
Pt 3, Ch 20, 2 General guidelines on inspection of mooring system components. For fibre rope, the industry standard such as CI 2001-04:
Fibre Rope Inspection and Retirement Criteria recognised by INTERTANKO can
be adopted as applicable.
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