SIST EN ISO 19901-7:2013

SLOVENSKI STANDARD
01-junij-2013
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SIST EN ISO 19901-7:2006
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Petroleum and natural gas industries - Specific requirements for offshore structures -
Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units
(ISO 19901-7:2013)
Erdöl- und Erdgasindustrie - Spezielle Anforderungen an Offshore-Bauwerke - Teil 7:
Betriebssysteme für die Stationsunterhalte schwimmender Anlagen und mobiler Offshore
-Einheiten (ISO 19901-7:2013)
Industries du pétrole et du gaz naturel - Exigences spécifiques relatives aux structures
en mer - Partie 7: Systèmes de maintien en position des structures en mer flottantes et
des unités mobiles en mer (ISO 19901-7:2013)
Ta slovenski standard je istoveten z: EN ISO 19901-7:2013
ICS:
75.180.10 Oprema za raziskovanje in Exploratory and extraction
odkopavanje equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 19901-7
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2013
ICS 75.180.10 Supersedes EN ISO 19901-7:2005
English Version
Petroleum and natural gas industries - Specific requirements for
offshore structures - Part 7: Stationkeeping systems for floating
offshore structures and mobile offshore units (ISO 19901-
7:2013)
Industries du pétrole et du gaz naturel - Exigences Erdöl- und Erdgasindustrie - Spezielle Anforderungen an
spécifiques relatives aux structures en mer - Partie 7: Offshore-Anlagen - Teil 7: Betriebssysteme für das
Systèmes de maintien en position des structures en mer Positionshalten schwimmender Anlagen und mobiler
flottantes et des unités mobiles en mer (ISO 19901-7:2013) Offshore-Einheiten (ISO 19901-7:2013)
This European Standard was approved by CEN on 5 January 2013.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19901-7:2013: E
worldwide for CEN national Members.

Contents Page
Foreword .3
Foreword
This document (EN ISO 19901-7:2013) has been prepared by Technical Committee ISO/TC 67 "Materials,
equipment and offshore structures for petroleum, petrochemical and natural gas industries" in collaboration
with Technical Committee CEN/TC 12 “Materials, equipment and offshore structures for petroleum,
petrochemical and natural gas industries” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by November 2013, and conflicting national standards shall be withdrawn
at the latest by November 2013.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 19901-7:2005.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 19901-7:2013 has been approved by CEN as EN ISO 19901-7:2013 without any modification.
INTERNATIONAL ISO
STANDARD 19901-7
Second edition
2013-05-01
Petroleum and natural gas industries —
Specific requirements for offshore
structures —
Part 7:
Stationkeeping systems for floating
offshore structures and mobile offshore
units
Industries du pétrole et du gaz naturel — Exigences spécifiques
relatives aux structures en mer —
Partie 7: Systèmes de maintien en position des structures en mer
flottantes et des unités mobiles en mer

Reference number
ISO 19901-7:2013(E)
©
ISO 2013
ISO 19901-7:2013(E)
©  ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
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Published in Switzerland
ii © ISO 2013 – All rights reserved

ISO 19901-7:2013(E)
Contents Page
Foreword . v
Introduction . vii
1  Scope . 1
2  Normative references . 2
3  Terms and definitions . 2
4  Symbols and abbreviated terms . 7
4.1  Symbols . 7
4.2  Abbreviated terms . 8
5  Overall considerations . 9
5.1  Functional requirements. 9
5.2  Safety requirements . 9
5.3  Planning requirements . 10
5.4  Inspection and maintenance requirements . 10
5.5  Analytical tools . 10
6  Design requirements . 10
6.1  Exposure levels . 10
6.2  Limit states . 11
6.3  Defining design situations . 11
6.4  Design situations . 12
7  Actions. 14
7.1  General . 14
7.2  Site-specific data requirements . 14
7.3  Environmental actions on mooring lines . 15
7.4  Indirect actions . 16
8  Mooring analysis . 18
8.1  Basic considerations . 18
8.2  Floating structure offset . 19
8.3  Floating structure response . 20
8.4  Mooring line response . 25
8.5  Line tension . 26
8.6  Line length and geometry constraints . 26
8.7  Anchor forces . 27
8.8  Typical mooring configuration analysis and assessment . 27
8.9  Thruster-assisted moorings . 28
8.10  Transient analysis of floating structure motions . 29
9  Fatigue analysis . 30
9.1  Basic considerations . 30
9.2  Fatigue resistance . 30
9.3  Fatigue analysis procedure . 32
10  Design criteria . 37
10.1  Floating structure offset . 37
10.2  Line tension limit . 38
10.3  Grounded line length . 38
10.4  Anchoring systems . 38
10.5  Fatigue safety factor . 41
10.6  Corrosion and wear . 41
10.7  Clearances . 42
ISO 19901-7:2013(E)
10.8  Supporting structures .42
11  Mooring hardware .42
11.1  Mooring line components .42
11.2  Winching equipment .43
11.3  Monitoring equipment .43
12  In-service inspection, monitoring and maintenance .44
12.1  General .44
12.2  Mobile moorings .44
12.3  Permanent moorings .44
13  Dynamic positioning system .46
13.1  Basic considerations .46
13.2  Design and analysis .47
13.3  Design, test and maintenance .48
13.4  Operating personnel .48
13.5  Determination of stationkeeping capability .48
14  Synthetic fibre rope mooring .48
14.1  Basic considerations .48
14.2  Fibre rope mooring analysis .49
14.3  Fatigue analysis .50
14.4  Creep analysis .50
14.5  Design criteria .50
14.6  Model testing .51
Annex A (informative) Additional information and guidance .52
Annex B (informative) Regional information . 169
Bibliography . 176

iv © ISO 2013 – All rights reserved

ISO 19901-7:2013(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 19901-7 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries, Subcommittee SC 7, Offshore structures.
This second edition cancels and replaces the first edition (ISO 19901-7:2005), which has been technically
revised.
This second edition of ISO 19901-7 includes several major additions and changes, primarily to Annex A
(informative). The largest change is the addition of detailed informative text incorporated directly from API RP
2SK on all types of anchor design. In the first edition of this International Standard, this material was
previously addressed only by reference to API RP 2SK. Informative material has also been added from
API RP 2SK regarding the analysis and mitigation of vortex-induced motions of large cylindrical hulls.
Consequently, the normative text has been modified to remove reference to API RP 2SK and to cross-
reference portions of the expanded informative annex.
The other significant change is the updating of guidance on polyester rope mooring design to conform to the
provisions of the recent amendment to API RP 2SM. The changes include new definitions of stiffness,
recognition of effective filter barriers, removal of the prohibition against the rope touching the sea floor, and
more detail on minimum tension requirements, among others. Additionally, minor corrections were made to
the text in 7.4.4 (Wind actions) and 8.3.4 (Riser considerations), and the terminology "most probable
maximum" has been standardized throughout. Finally, the Norwegian clause of Annex B has been updated at
the request of Norway, and a new Canadian clause has been added.
ISO 19901 consists of the following parts, under the general title Petroleum and natural gas industries —
Specific requirements for offshore structures:
 Part 1: Metocean design and operating considerations
 Part 2: Seismic design procedures and criteria
 Part 3: Topsides structure
 Part 4: Geotechnical and foundation design considerations
 Part 5: Weight control during engineering and construction
 Part 6: Marine operations
 Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units
ISO 19901-7:2013(E)
The following parts are under preparation:
 Part 8: Marine soil investigations
ISO 19901 is one of a series of International Standards for offshore structures. The full series consists of the
following International Standards:
 ISO 19900, Petroleum and natural gas industries — General requirements for offshore structures
 ISO 19901 (all parts), Petroleum and natural gas industries — Specific requirements for offshore
structures
 ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
 ISO 19903, Petroleum and natural gas industries — Fixed concrete offshore structures
 ISO 19904-1, Petroleum and natural gas industries — Floating offshore structures — Part 1: Monohulls,
semi-submersibles and spars
 ISO 19905-1, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
units — Part 1: Jack-ups
 ISO/TR 19905-2, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
units — Part 2: Jack-ups commentary and detailed sample calculation
 ISO 19905-3, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
1)
units — Part 3: Floating units
 ISO 19906, Petroleum and natural gas industries — Arctic offshore structures

1) Under preparation.
vi © ISO 2013 – All rights reserved

ISO 19901-7:2013(E)
Introduction
The series of International Standards applicable to types of offshore structure, ISO 19900 to ISO 19906,
constitutes a common basis covering those aspects that address design requirements and assessments of all
offshore structures used by the petroleum, petrochemical and natural gas industries worldwide. Through their
application, the intention is to achieve reliability levels appropriate for manned and unmanned offshore
structures, whatever type of structure and nature or combination of materials used.
It is important to recognize that structural integrity is an overall concept comprising models for describing
actions, structural analyses, design rules, safety elements, workmanship, quality control procedures and
national requirements, all of which are mutually dependent. The modification of one aspect of design in
isolation can disturb the balance of reliability inherent in the overall concept or structural system. The
implications involved in modifications therefore need to be considered in relation to the overall reliability of all
offshore structural systems.
The series of International Standards applicable to types of offshore structure is intended to provide wide
latitude in the choice of structural configurations, materials and techniques without hindering innovation.
Sound engineering judgement is therefore necessary in the use of these International Standards.
This part of ISO 19901 was developed in response to the worldwide offshore industry’s demand for a coherent
and consistent definition of methodologies to analyse, design and evaluate stationkeeping systems used for
floating production and/or storage platforms of various types (e.g. semi-submersibles, spar platforms, ship-
shaped structures) and to assess site-specific applications of mobile offshore units (such as mobile offshore
drilling units, pipelay units, construction units).
Stationkeeping is a generic term covering systems for keeping a floating structure, which is under the constant
influence of external actions, on a pre-defined location and/or heading with limited excursions. Stationkeeping
systems resist external actions by means of any combination of the following:
 mooring systems (e.g. spread moorings or single point moorings);
 dynamic positioning systems (generally consisting of thrusters).
The external actions generally consist of wind, wave, current and ice actions on the floating structure, mooring
and/or risers.
Some background to, and guidance on, the use of this part of ISO 19901 is provided in informative Annex A.
The clause numbering in Annex A is the same as in the normative text to facilitate cross-referencing.
Regional information, where available, is provided in informative Annex B.

INTERNATIONAL STANDARD ISO 19901-7:2013(E)

Petroleum and natural gas industries — Specific requirements
for offshore structures —
Part 7:
Stationkeeping systems for floating offshore structures and
mobile offshore units
1 Scope
This part of ISO 19901 specifies methodologies for
a) the design, analysis and evaluation of stationkeeping systems for floating structures used by the oil and
gas industries to support
1) production,
2) storage,
3) drilling, well intervention and production,
4) production and storage,
5) drilling, well intervention, production and storage, and
b) the assessment of stationkeeping systems for site-specific applications of mobile offshore units (e.g.
mobile offshore drilling units, construction units, and pipelay units).
Most stationkeeping systems used with the class of floating structures covered by a) are termed “permanent
mooring systems”, for which this part of ISO 19901 is applicable to all aspects of the life cycle and includes
requirements relating to the manufacture of mooring components, as well as considerations for in-service
inspections. Most stationkeeping systems used with mobile offshore units, the class covered by b), are termed
“mobile mooring systems”. Throughout this part of ISO 19901, the term “floating structure”, sometimes
shortened to “structure”, is used as a generic term to indicate any member of the two classes, a) and b).
This part of ISO 19901 is applicable to the following types of stationkeeping systems, which are either covered
directly in this part of ISO 19901 or through reference to other guidelines:
 spread moorings (catenary, taut-line and semi-taut-line moorings);
 single point moorings, anchored by spread mooring arrangements;
 dynamic positioning systems;
 thruster-assisted moorings.
Descriptions of the characteristics and of typical components of these systems are given in Annex A.
The requirements of this part of ISO 19901 mainly address spread mooring systems and single point mooring
systems with mooring lines composed of steel chain and wire rope. This part of ISO 19901 also provides
ISO 19901-7:2013(E)
guidance on the application of the methodology to synthetic fibre rope mooring systems, and includes
additional requirements related to the unique properties of synthetic fibre ropes.
This part of ISO 19901 is applicable to single anchor leg moorings (SALMs) and other single point mooring
systems (e.g. tower soft yoke systems) only to the extent to which the requirements are relevant.
This part of ISO 19901 is not applicable to the vertical moorings of tension leg platforms (TLPs).
The methodology described in this part of ISO 19901 identifies a set of coherent analysis tools that, combined
with an understanding of the site-specific metocean conditions, the characteristics of the floating structure
under consideration, and other factors, can be used to determine the adequacy of the stationkeeping system
to meet the functional requirements of this part of ISO 19901.
NOTE For moorings deployed in ice-prone environments, additional requirements are given in ISO 19906.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 19900, Petroleum and natural gas industries — General requirements for offshore structures
ISO 19901-1, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 1:
Metocean design and operating considerations
ISO 19904-1, Petroleum and natural gas industries — Floating offshore structures — Part 1: Monohulls, semi-
submersibles and spars
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
action
external load applied to the structure (direct action) or an imposed deformation or acceleration (indirect action)
EXAMPLE An imposed deformation can be caused by fabrication tolerances, settlement, temperature change or
moisture variation.
NOTE An earthquake typically generates imposed accelerations.
[ISO 19900:2002]
3.2
action effect
effect of actions on structural components
[ISO 19900:2002]
EXAMPLE Internal forces, moments, stresses, strains, rigid body motions or elastic deformations.
3.3
catenary mooring
mooring system where the restoring action is provided by the distributed weight of mooring lines
[ISO 19900:2002]
2 © ISO 2013 – All rights reserved

ISO 19901-7:2013(E)
3.4
characteristic value
value assigned to a basic variable, an action or a resistance from which the design value can be found by the
application of a partial factor
NOTE 1 The value usually has a prescribed probability of not being violated which, in the case of an action, will
normally relate to a reference period.
NOTE 2 Adapted from ISO 19900:2002, definition 2.7.
3.5
design criteria
quantitative formulations that describe the conditions to be fulfilled for each limit state
[ISO 19900:2002]
3.6
design service life
assumed period for which a structure or a structural component is to be used for its intended purpose with
anticipated maintenance, but without substantial repair being necessary
NOTE Adapted from ISO 19900:2002, definition 2.12.
3.7
design situation
set of physical conditions during a certain reference period for which the design will demonstrate that relevant
limit states are not exceeded
NOTE Adapted from ISO 19900:2002, definition 2.13.
3.8
dynamic action
action that induces acceleration of a structure or a structural component of a magnitude sufficient to require
specific consideration
3.9
dynamic positioning
DP
stationkeeping technique consisting primarily of a system of automatically controlled on-board thrusters, which
generate appropriate thrust vectors to counter the mean and slowly varying induced actions
3.10
expected value
first-order statistical moment of the probability density function for the considered variable that, in the case of a
time-dependent parameter, can be associated with a specific reference period
3.11
fit-for-purpose
fitness-for-purpose
meeting the intent of an International Standard although not meeting specific provisions of that International
Standard in local areas, such that failure in these areas will not cause unacceptable risk to life-safety or the
environment
[ISO 19900:2002]
ISO 19901-7:2013(E)
3.12
floating structure
structure where the full weight is supported by buoyancy
[ISO 19900:2002]
NOTE The full weight includes lightship weight, mooring system pre-tension, riser pre-tension, operating weight, etc.
3.13
limit state
state beyond which the structure no longer fulfils the relevant design criteria
[ISO 19900:2002]
3.14
maintenance
set of activities performed during the operating life of a structure to ensure it is fit-for-purpose
3.15
minimum breaking strength
MBS
RCS certified strength of a chain, wire rope, fibre rope or accessories
3.16
mobile mooring system
mooring system, generally retrievable, intended for deployment at a specific location for a short-term operation,
such as those for mobile offshore units (MOUs)
3.17
mobile offshore drilling unit
MODU
structure capable of engaging in drilling and well intervention operations for exploration or exploitation of
subsea petroleum resources
3.18
mobile offshore unit
MOU
structure intended to be frequently relocated to perform a particular function
[ISO 19900:2002]
EXAMPLE Pipelaying vessel or barge, offshore construction structure, accommodation structure (floatel), service
structure, or mobile offshore drilling units.
3.19
mooring component
general class of component used in the mooring of floating structures
EXAMPLE Chain, steel wire rope, synthetic fibre rope, clump weight, buoy, winch/windlass, fairlead or anchor.
3.20
owner
representative of the company or companies which own a development, who can be the operator on behalf of
co-licensees
3.21
permanent mooring system
mooring system normally used to moor floating structures deployed for long-term operations, such as those
for a floating production system (FPS)
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ISO 19901-7:2013(E)
3.22
proximity
closeness in distance
NOTE 1 Mooring systems are considered to be in proximity to a surface installation (or facility) if any part of the other
installation lies within a contour described by the set of offsets coinciding with each line reaching 100 % MBS in the intact
or redundancy check condition, whichever is larger.
NOTE 2 Mooring systems are considered to be in proximity to a sea floor installation (or facility) if any part of the other
installation lies within a polygon formed by the anchor locations.
3.23
RCS
recognized classification society
member of the international association of classification societies (IACS), with recognized and relevant
competence and experience in floating structures, and with established rules and procedures for
classification/certification of installations used in petroleum-related activities
3.24
resistance
capacity of a structure, a component or a cross-section of a component to withstand action effects without
exceeding a limit state
NOTE This definition is at variance with that specified in ISO 19900:2002.
3.25
return period
average period between occurrences of an event or of a particular value being exceeded
NOTE The offshore industry commonly uses a return period measured in years for environmental events. The return
period is equal to the reciprocal of the annual probability of exceedance of the event.
[ISO 19901-1:2005]
3.26
riser
piping connecting the process facilities or drilling equipment on the floating structure with the subsea facilities
or pipelines, or reservoir
NOTE 1 Possible functions include drilling and well intervention, production, injection, subsea systems control and
export of produced fluids.
NOTE 2 Adapted from ISO 19900:2002, definition 2.29.
3.27
semi-submersible
floating structure normally consisting of a deck structure with a number of widely spaced, large cross-section,
supporting columns connected to submerged pontoons
NOTE Pontoon/column geometry is usually chosen to minimize global motions in a broad range of wave frequencies.
3.28
serviceability
ability of a structure or structural component to perform adequately for normal functional use
3.29
significant value
statistical measure of a zero-mean random variable equal to twice the standard deviation of the variable
ISO 19901-7:2013(E)
3.30
single point mooring
mooring system that allows the floating structure to which it is connected to vary its heading (weathervane)
EXAMPLE One example of a single point mooring is a turret mooring system where a number of mooring lines are
attached to a turret, which includes bearings to allow the structure to rotate.
3.31
ship-shaped structure
monohull floating structure having a geometry similar to that of ocean-going ships
3.32
spar platform
deep-draught, small water-plane area floating structure
3.33
spread mooring
mooring system consisting of multiple mooring lines terminated at different locations on a floating structure,
and extending outwards, providing an almost constant structure heading
3.34
stationkeeping system
system capable of limiting the excursions of a floating structure within prescribed limits
3.35
structural component
physically distinguishable part of a structure
[ISO 19900:2002]
3.36
structure
organized combination of connected components designed to withstand actions and provide adequate rigidity
[ISO 19900:2002]
3.37
taut-line mooring
mooring system where the restoring action is provided by elastic deformation of mooring lines
[ISO 19900:2002]
3.38
thruster-assisted mooring
stationkeeping system consisting of mooring lines and thrusters
3.39
verification
examination made to confirm that an activity, product, or service is in accordance with specified requirements
3.40
weathervaning
process by which a floating structure passively varies its heading in response to time-varying environmental
actions
6 © ISO 2013 – All rights reserved

ISO 19901-7:2013(E)
4 Symbols and abbreviated terms
4.1 Symbols
C coefficient (non-dimensional unless otherwise specified)
–1
D annual fatigue damage, in years
d diameter of the mooring line or component, in metres (m)
F direct action, in newtons (N), or a direct action per unit length, in newtons per metre, (N/m)
f frequency, in hertz (Hz)
K fatigue constant (non-dimensional unless otherwise specified)
k axial stiffness, in newtons per metre (N/m)
L design service life, in years

l length, in metres (m)
M mass, in kilograms (kg)
m inverse slope of T-N or S-N fatigue curves
N total number of (permissible) cycles
-1
n number of cycles per annum, in year
P probability of occurrence
S offset or motion, in metres (m)
S stress range, in megapascals (MPa)
R
s standard deviation
T tension force, in newtons (N); or non-dimensional tension ratio
t time, period or duration, in seconds (s)
v velocity, in metres per second (m/s)
W submerged weight, in newtons (N), or weight per unit length, in newtons per metre (N/m)
 gamma function
 design safety factor 
 bandwidth parameter for the wave frequency
 annual creep elongation, percent per year
 ratio of the standard deviation of the tension variations around the mean tension to a reference breaking
strength
 density, in kilograms per cubic metre (kg/m )
ISO 19901-7:2013(E)
4.2 Abbreviated terms
ALS accidental limit state
CALM catenary anchor leg mooring
DP dynamic positioning
FEA finite element analysis
FLS fatigue limit state
FMEA failure modes and effects analysis
FPS floating production system
FPSO floating production, storage and offloading structure
FSO floating storage and offloading structure
HMPE high modulus polyethylene
IACS International Association of Classification Societies
IMCA International Marine Contractors Association
IMO International Maritime Organization
LTM long-term mooring
MBS minimum breaking strength
MDS mooring design states
MODU mobile offshore drilling unit
MOU mobile offshore unit
ORQ oil rig quality
RAO response amplitude operator
RCS recognized classification society
ROV remotely operated vehicle
SALM single anchor leg mooring
SAW submerged arc welding
SIM structural integrity management
SLS serviceability limit state
TAM thruster-assisted mooring
TLP tension leg platform
ULS ultimate limit state
VIM vortex-induced motion
VIV vortex-induced vibration
8 © ISO 2013 – All rights reserved

ISO 19901-7:2013(E)
5 Overall considerations
5.1 Functional requirements
The function of a stationkeeping system is to restrict the horizontal excursion of a floating structure within
prescribed limits, as well as to provide means of active or passive directional control when the structure’s
orientation is important for safety or operational considerations.
The limiting criteria for excursions and orientation are generally established either by the owner of the floating
structure or by direct derivation from design requirements including those related to
 safety of personnel,
 protection of the environment,
 stability and serviceability of the floating structure,
 serviceability of the topsides equipment,
 integrity and serviceability of drilling, production, export or other types of risers,
 access to and clearances with respect to nearby subsea or surface installations, and
 any other special positioning requirement.
Compliance of the stationkeeping system design with the requirements outlined above shall be established
using the analysis methodologies given in Clauses 8 and 9, and the design criteria specified in Clause 10. The
effects of external actions on the floating structure such as line tensions, structure offsets and anchor forces
shall be evaluated for all relevant design situations, and shall be compared with the system and component
resistances to ensure the existence of reserve strengths against mooring line breakage, offset exceedance,
anchor slippage or other undesirable occurrences.
5.2 Safety requirements
Safety of life, environment and property shall be the main principles to be respected at all times through
 competent design or assessment, which ensures the ability of the floating structure and its stationkeeping
system to withstand environmental and other external actions likely to occur during the design service
lives of the structure and stationkeeping system, or duration of site-specific deployment of an MOU,
 definition of safe operating procedures so that risks of injuries to personnel are identified and minimized,
 identification and assessment of possible accidental events, as summarized in ISO 19900, and
minimization of their consequences,
 performance of a risk assessment to ensure that possible malfunctions do not pose a danger to life or
structure integrity, and
 compliance with all relevant regulations, see ISO 19904-1.
The implications of the above items shall be incorporated in the stationkeeping system design or assessment,
and in the development of the operational philosophy.
ISO 19901-7:2013(E)
5.3 Planning requirements
Planning shall be carried out before actual design or assessment is started in order to ensure that the
stati
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