SIST EN ISO 19901-7:2026
(Main)Specific requirements for offshore structures - Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units (ISO 19901-7:2026)
- Abstract
This document specifies methodologies for:
the design, analysis and evaluation of stationkeeping systems for floating offshore structures;
the assessment of stationkeeping systems for site-specific applications of mobile offshore units and construction units.
Originally developed for floating structures used in the oil and gas industry, this document is now also used in the renewable energy sector. The extent of application of this document to floating structures used in other industries is at the discretion of the relevant standard entity and its users. For example, IEC 61400-3-2 for floating wind applies this document to determine stationkeeping system responses while incorporating its own load conditions, safety factors, and environmental return periods.
This document is applicable to the following types of stationkeeping systems, which are either covered directly in this document or through reference to other guidelines:
spread mooring systems;
single point mooring systems;
dynamic positioning systems;
thruster-assisted mooring systems.
This document is not applicable to:
stationkeeping systems which do not have redundancy against failure of any single component, e.g., single anchor leg moorings (SALMs);
stationkeeping systems which use any means other than mooring lines or thrusters such as tower soft yoke systems, or tension leg platforms (TLPs) that use tendons.
The requirements for this document address spread mooring systems and single point mooring systems with mooring lines composed of steel chain, steel wire or synthetic fibre rope.
This document is applicable to all aspects of the life cycle of mooring systems. It includes requirements relating to the selection of mooring components, mooring system configuration and performance, components design, installation, post-installation survey, and as-installed assessments as needed for mooring integrity management.
For mooring systems deployed in ice-prone environments, additional requirements in ISO 19906 apply.
- Status
- Published
- Public Enquiry End Date
- 30-Dec-2024
- Publication Date
- 24-Aug-2026
- Technical Committee
- I13 - Imaginarni 13
- Current Stage
- 6060 - National Implementation/Publication (Adopted Project)
- Start Date
- 11-Aug-2026
- Due Date
- 16-Oct-2026
- Completion Date
- 25-Aug-2026
SIST EN ISO 19901-7:2026 is the CEN-adopted European Standard for stationkeeping systems for floating offshore structures and for the site-specific assessment of mobile offshore units and construction units. It specifies methodologies for design, analysis and evaluation, and it is used for spread mooring, single point mooring, dynamic positioning (DP) and thruster-assisted mooring (TAM) systems. The document is meant for designers, operators, verifiers and inspection teams working in offshore oil and gas, and it is also applied in the renewable energy sector where users choose to adopt it.
What does SIST EN ISO 19901-7:2026 specify?
SIST EN ISO 19901-7:2026 specifies the methodologies used to plan, design, analyze and assess stationkeeping systems for floating offshore structures, and to assess stationkeeping systems for site-specific use on mobile offshore units and construction units. It also sets the life-cycle framework for components, installation, survey, and integrity management.
The document applies to these stationkeeping system types:
| Annex | What it covers |
|---|---|
| Annex A (informative) | Additional information and guidance, including examples, figures, analysis guidance and inspection advice. |
| Annex B (normative) | Regional requirements and supporting information, including regional clauses for Norway, Canada and the USA: Gulf of Mexico. |
The scope includes spread mooring systems, single point mooring systems, dynamic positioning systems and thruster-assisted mooring systems. It is not intended for systems without redundancy against failure of any single component, or for systems that rely on means other than mooring lines or thrusters, such as tower soft yoke systems or tendon-based tension leg platforms (TLPs).
The document focuses on mooring lines made of steel chain, steel wire or synthetic fibre rope, and it covers the full mooring life cycle. That matters in practice because the same standard is used to select components, define the layout, check performance, manage installation, and support later surveys and as-installed assessments.
What are the key requirements of SIST EN ISO 19901-7:2026?
Component selection, quality and interfaces
Clause 4 treats the mooring system as a complete assembly from anchor to the connection on the floating structure. SIST EN ISO 19901-7:2026 requires an operator-approved quality plan for mooring hardware, plus review of manufacturing tolerances, fit-up tests, and a clear interface management plan between operator, designer, contractor and manufacturers.
In practice, this means the system should be designed as an integrated chain of parts, not as separate pieces. The standard also states that the design philosophy should make sure equipment or mooring components fail before the supporting foundations fail, which helps avoid hidden weak points in the structure.
Site data and environmental conditions
Clause 5 requires metocean, bathymetric, geotechnical, geophysical, marine growth, physicochemical and ice-related data to be defined for the site. Bathymetry and seabed surveys are tied to anchor positions and clearances, while soil characterization supports anchor design and holding capacity. For ice-prone environments, ISO 19906 applies.
This matters because stationkeeping performance depends on the actual site, not only on the nominal system design. The standard expects the designer to use site data deep enough and broad enough to cover anchor influence zones, degradation mechanisms and any environmental factors that affect loads or materials.
Functional safety, design basis and verification
Clause 6 requires the stationkeeping system to meet its functional limits on excursion and heading, while also protecting personnel, the environment, the structure and connected risers or topsides equipment. SIST EN ISO 19901-7:2026 also requires the operator to define the rules and regulations that apply, with their order of precedence.
For permanent systems, the standard calls for independent verification of design, manufacturing and installation, and it allows this to be supported by classing. It also expects the designer to document analysis tools and modeling protocols, which is important when software results are used to support safety decisions. Design work is organized by limit state and design situation, including ultimate, serviceability, fatigue, abnormal, accidental and temporary phases.
Acceptance criteria: offsets, clearances and fatigue
Clause 7 sets the criteria for line tensions, buoyancy elements and anchor holding capacity, and it places responsibility for offset and heading limits with the operator. The standard also requires clearances to be checked against the seabed, sea surface, hull, risers, umbilicals, pipelines, seabed assets and exclusion zones.
Clause 7.4 requires fatigue resistance to be assessed with Miner's rule, using either a tension-range T-N approach or a stress-range S-N approach. The operator chooses the method, but the safety factors and curve selection must match that method. The clause also brings VIM fatigue into the calculation and expects corrosion and wear to be accounted for when reference breaking strength is used.
Analysis methods and response checks
Clause 8 requires mooring analysis for the design situations defined earlier in the standard, and the calculated responses must be checked against the criteria in Clause 7. SIST EN ISO 19901-7:2026 allows frequency-domain, time-domain, or combined approaches, but it requires line dynamics to be included. Quasi-static methods are not acceptable for final design of permanent systems or final site-specific assessment of MOU moorings.
This section also requires the analysis to include coupling with risers, the effect of marine growth, seabed slope and trenching, and sensitivity checks on critical cases. Response-based analysis (RBA) is also described as a way to estimate extreme responses from long-term response statistics rather than only from the environmental condition itself.
DP, TAM and operational redundancy
Clause 9 sets out the stationkeeping rules for dynamic positioning (DP) and thruster-assisted mooring (TAM). The document uses DP equipment classes 1, 2 and 3 to express redundancy, and it requires the available effective thrust to be determined and then reduced for the worst single failure when applicable.
In practice, this means the operating class must match the consequence of losing position or heading. FMEA, proving trials, annual surveys, annual tests and trained operating personnel are part of the DP/TAM package, and the holding capability analysis must check whether the vessel can stay within its acceptable watch circle under the relevant limit state.
Installation, as-installed condition and integrity management
Clauses 10 and 11 carry the standard into offshore installation and long-term service. SIST EN ISO 19901-7:2026 requires constructability review, storm-safe criteria, installation procedures, tolerances, traceability records, as-installed surveys and post-installation capacity assessment.
The integrity side is handled through a mooring integrity management (MIM) program, periodic inspections, conformity assessment, fitness-for-service checks and monitoring of position, heading and line failure. That matters because the design basis only remains valid if the installed system is tracked, inspected and updated over time.
What terms does SIST EN ISO 19901-7:2026 define?
- active stationkeeping system - a stationkeeping system that changes its position-keeping response through DP, thruster assistance, line length or pretension adjustment, draught changes, winching off location or disconnection.
- catenary mooring system - a mooring system where restoring action comes from both the weight of the line and its strain deformation.
- damaged condition - the state of the stationkeeping system after a line is missing or weakened, or after a thruster failure, including the critical damaged case for thruster-assisted systems.
- design situation - the set of physical conditions under which the structure or component is verified.
- dynamic positioning (DP) - a stationkeeping method that uses thrusters and control systems to hold position and heading.
- mooring integrity management (MIM) - the facility-specific program used to maintain mooring integrity from design stage through the design service life.
- weathervaning - the passive change of a floating structure's heading in response to changing environmental actions.
Who uses SIST EN ISO 19901-7:2026?
SIST EN ISO 19901-7:2026 is used by mooring engineers, offshore structural designers, marine operations planners, operators, class societies, independent verifiers and inspection teams. They use it for design, site-specific assessment, installation planning, as-installed checks, survey planning and integrity management.
It is relevant to floating offshore structures in oil and gas, lower-carbon energy and renewable energy projects. It is also used for mobile offshore units and construction units when a location-specific stationkeeping assessment is needed.
Quality and procurement teams use it to define component specifications, quality plans, interface responsibilities and traceability expectations. Surveyors and integrity managers use it for inspection intervals, fitness-for-service work and monitoring of condition changes over time.
What changed in SIST EN ISO 19901-7:2026 from the previous edition?
SIST EN ISO 19901-7:2026 supersedes EN ISO 19901-7:2013.
Which standards are used with SIST EN ISO 19901-7:2026?
SIST EN ISO 19901-7:2026 relies on the following references and companion documents to complete the design and assessment framework:
| Reference | What it contributes |
|---|---|
| ISO 19900 | General offshore structure requirements and shared concepts such as action, design situation and verification. |
| ISO 19901-1 | Metocean design and operating considerations. |
| ISO 19901-4 | Geotechnical design considerations. |
| ISO 19901-6 | Marine operations for planning installation and handling. |
| ISO 19901-8 | Marine soil investigations. |
| ISO 19901-10 | Marine geophysical investigations and bathymetry / seabed survey. |
| ISO 19904-1 | Floating offshore structures context for mooring and related structure behavior. |
| ISO 19905-3 | Site-specific assessment of mobile offshore units. |
| ISO 19906 | Arctic offshore structures and ice-related conditions. |
| ISO 18692-1 | Fibre ropes for offshore stationkeeping and rope property guidance. |
| ISO 20438 | Offshore mooring chains. |
| ISO 31000 | Risk management framework used for DP and other risk-based decisions. |
| IMO MSC.1/Circ.1580 | DP guidance used for failure analysis and operational practice. |
| IACS UR W22 | Offshore mooring chain requirements. |
| API RP 2I | In-service inspection of mooring hardware. |
| API RP 2MIM | Mooring integrity management. |
| API SPEC 9A | Wire rope specification. |
| ASME Section VIII, Division 1 | Pressure vessel rules referenced where applicable to components. |
| DNV-OS-E301, DNV-RP-E301, DNV-RP-E302, DNV-RP-E303 | Position mooring and anchor design / installation guidance. |
| MTS DP operations guidance | DP operational guidance used with risk assessment and operating practice. |
What does the SIST EN ISO 19901-7:2026 document contain?
SIST EN ISO 19901-7:2026 contains the full framework for stationkeeping systems, from terminology through installation and integrity management. Clause 3 defines terms, symbols and abbreviations, while Clauses 4 and 5 cover hardware, site data and environmental inputs.
The technical core is split across Clauses 6 to 11. These clauses include the design basis, safety requirements, analysis methods, fatigue formulas and safety factors, DP and TAM requirements, installation and test loading, and the long-term inspection and monitoring program.
Annex A adds guidance material rather than new mandatory text. It includes system examples, guidance on analysis methods, fatigue assessment, response-based analysis, installation practice and inspection methods, together with figures that illustrate mooring arrangements, response statistics and inspection workflows.
Annex B gives regional requirements and supporting information. It includes regional clauses for Norway, Canada and the USA: Gulf of Mexico, so users working in those areas can combine the main document with local practice and regulatory expectations.
Relations
- Effective Date
- 05-Aug-2026
- Effective Date
- 19-Jan-2023
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Frequently Asked Questions
SIST EN ISO 19901-7:2026 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "Specific requirements for offshore structures - Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units (ISO 19901-7:2026)". This standard covers: This document specifies methodologies for: the design, analysis and evaluation of stationkeeping systems for floating offshore structures; the assessment of stationkeeping systems for site-specific applications of mobile offshore units and construction units. Originally developed for floating structures used in the oil and gas industry, this document is now also used in the renewable energy sector. The extent of application of this document to floating structures used in other industries is at the discretion of the relevant standard entity and its users. For example, IEC 61400-3-2 for floating wind applies this document to determine stationkeeping system responses while incorporating its own load conditions, safety factors, and environmental return periods. This document is applicable to the following types of stationkeeping systems, which are either covered directly in this document or through reference to other guidelines: spread mooring systems; single point mooring systems; dynamic positioning systems; thruster-assisted mooring systems. This document is not applicable to: stationkeeping systems which do not have redundancy against failure of any single component, e.g., single anchor leg moorings (SALMs); stationkeeping systems which use any means other than mooring lines or thrusters such as tower soft yoke systems, or tension leg platforms (TLPs) that use tendons. The requirements for this document address spread mooring systems and single point mooring systems with mooring lines composed of steel chain, steel wire or synthetic fibre rope. This document is applicable to all aspects of the life cycle of mooring systems. It includes requirements relating to the selection of mooring components, mooring system configuration and performance, components design, installation, post-installation survey, and as-installed assessments as needed for mooring integrity management. For mooring systems deployed in ice-prone environments, additional requirements in ISO 19906 apply.
This document specifies methodologies for: the design, analysis and evaluation of stationkeeping systems for floating offshore structures; the assessment of stationkeeping systems for site-specific applications of mobile offshore units and construction units. Originally developed for floating structures used in the oil and gas industry, this document is now also used in the renewable energy sector. The extent of application of this document to floating structures used in other industries is at the discretion of the relevant standard entity and its users. For example, IEC 61400-3-2 for floating wind applies this document to determine stationkeeping system responses while incorporating its own load conditions, safety factors, and environmental return periods. This document is applicable to the following types of stationkeeping systems, which are either covered directly in this document or through reference to other guidelines: spread mooring systems; single point mooring systems; dynamic positioning systems; thruster-assisted mooring systems. This document is not applicable to: stationkeeping systems which do not have redundancy against failure of any single component, e.g., single anchor leg moorings (SALMs); stationkeeping systems which use any means other than mooring lines or thrusters such as tower soft yoke systems, or tension leg platforms (TLPs) that use tendons. The requirements for this document address spread mooring systems and single point mooring systems with mooring lines composed of steel chain, steel wire or synthetic fibre rope. This document is applicable to all aspects of the life cycle of mooring systems. It includes requirements relating to the selection of mooring components, mooring system configuration and performance, components design, installation, post-installation survey, and as-installed assessments as needed for mooring integrity management. For mooring systems deployed in ice-prone environments, additional requirements in ISO 19906 apply.
SIST EN ISO 19901-7:2026 is classified under the following ICS (International Classification for Standards) categories: 75.180.10 - Exploratory, drilling and extraction equipment. The ICS classification helps identify the subject area and facilitates finding related standards.
SIST EN ISO 19901-7:2026 has the following relationships with other standards: It is inter standard links to SIST EN IEC 61400-3-2:2025, SIST EN ISO 19901-7:2013. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
SIST EN ISO 19901-7:2026 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
SLOVENSKI STANDARD
01-oktober-2026
Posebne zahteve za naftne ploščadi - 7. del: Sistemi za vzdrževanje postaj na
plavajočih strukturah in premičnih enotah (ISO 19901-7:2026)
Specific requirements for offshore structures - Part 7: Stationkeeping systems for floating
offshore structures and mobile offshore units (ISO 19901-7:2026)
Öl- und Gasindustrie einschließlich kohlenstoffarmer Energieträger - Spezielle
Anforderungen für Offshore-Bauwerke - Teil 7: Positions-Erhaltungssysteme für
schwimmende Offshore-Bauwerke und mobile Offshore-Einheiten (ISO 19901-7:2026)
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-
7:2026)
Ta slovenski standard je istoveten z: EN ISO 19901-7:2026
ICS:
75.180.10 Oprema za raziskovanje, Exploratory, drilling and
vrtanje in odkopavanje extraction equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 19901-7
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2026
EUROPÄISCHE NORM
ICS 75.180.10 Supersedes EN ISO 19901-7:2013
English Version
Specific requirements for offshore structures - Part 7:
Stationkeeping systems for floating offshore structures
and mobile offshore units (ISO 19901-7:2026)
Exigences spécifiques relatives aux structures en mer - Öl- und Gasindustrie einschließlich kohlenstoffarmer
Partie 7: Systèmes de maintien en position des Energieträger - Spezielle Anforderungen für Offshore-
structures en mer flottantes et des unités mobiles en Bauwerke - Teil 7: Positions-Erhaltungssysteme für
mer (ISO 19901-7:2026) schwimmende Offshore-Bauwerke und mobile
Offshore-Einheiten (ISO 19901-7:2026)
This European Standard was approved by CEN on 5 June 2026.
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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19901-7:2026 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 19901-7:2026) has been prepared by Technical Committee ISO/TC 67 "Oil and
gas industries including lower carbon energy" in collaboration with Technical Committee CEN/TC 12
“Oil and gas industries including lower carbon energy” the secretariat of which is held by NEN.
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 January 2027, and conflicting national standards shall
be withdrawn at the latest by January 2027.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 19901-7:2013.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
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, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 19901-7:2026 has been approved by CEN as EN ISO 19901-7:2026 without any
modification.
International
Standard
ISO 19901-7
Third edition
Specific requirements for offshore
2026-07
structures —
Part 7:
Stationkeeping systems for floating
offshore structures and mobile
offshore units
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 19901-7:2026(en) © ISO 2026
ISO 19901-7:2026(en)
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii
ISO 19901-7:2026(en)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 2
3 Terms, definitions, symbols and abbreviated terms .3
3.1 Terms and definitions .3
3.2 Symbols . 12
3.3 Abbreviated terms . 13
4 Mooring hardware . 14
4.1 General .14
4.2 Off-vessel mooring line components . 15
4.2.1 General . 15
4.2.2 Anchors . 15
4.2.3 Chain . 15
4.2.4 Fibre rope. 15
4.2.5 Steel wire rope . 15
4.2.6 Connecting hardware .16
4.2.7 Buoys . .16
4.2.8 Clump weights .16
4.2.9 Mooring connectors . .16
4.2.10 Disconnectable turret buoy .17
4.3 On-vessel mooring line components .17
4.3.1 General .17
4.3.2 Fairleads . .17
4.3.3 Bending shoes .17
4.3.4 Chain stoppers .17
4.3.5 Uni-joints .17
4.3.6 Turret .17
4.4 On-vessel tensioning equipment .18
4.5 Monitoring equipment .18
4.5.1 General .18
4.5.2 Line tension or line payout .18
4.5.3 Floating structure position and heading .19
5 Metocean and other site data . 19
5.1 General .19
5.2 Metocean data .19
5.2.1 General .19
5.2.2 Wave data .19
5.2.3 Wind data . 20
5.2.4 Current data. 20
5.3 Bathymetry . 20
5.4 Geotechnical and geophysical data . 20
5.5 Marine growth .21
5.6 Physicochemical parameters .21
5.7 Ice-related .21
6 Design and site-specific assessment of stationkeeping systems .21
6.1 General .21
6.2 Functional requirements .21
6.3 Safety requirements . 22
6.4 Planning requirements . 23
6.4.1 General . 23
6.4.2 Design basis . 23
6.4.3 Design practices . 23
iii
ISO 19901-7:2026(en)
6.4.4 Installation considerations at design stage .24
6.4.5 Integrity management strategy .24
6.5 Rules and regulations . 25
6.6 Independent verification for permanent systems . 25
6.7 Numerical tools . 25
6.8 Design situations . 25
6.8.1 Limit states . 25
6.8.2 Analysis cases for ultimate limit state . 26
6.8.3 Analysis cases for serviceability limit state . 28
6.8.4 Analysis cases for fatigue limit state. 29
6.8.5 Analysis cases for abnormal and accidental limit states . 30
6.8.6 Analysis cases for temporary phases . 30
7 Design and site-specific assessment criteria .31
7.1 Safety factors for mooring component strength .31
7.1.1 Line tensions .31
7.1.2 Safety factors for buoyancy elements . 33
7.1.3 Anchor holding capacity safety factors . 33
7.2 Vessel offsets and heading . 35
7.3 Requirements for clearances . 35
7.3.1 General . 35
7.3.2 Mooring line with seabed (thrash zone) . 35
7.3.3 Mooring line with sea surface . 36
7.3.4 Mooring line with hull . 36
7.3.5 Mooring line with riser, umbilical, mooring line, pipeline, seabed assets and
exclusion zones . 36
7.3.6 Submerged turret buoy .37
7.3.7 Anchor with mooring line, pipeline, seabed assets and exclusion zones .37
7.4 Safety factors for mooring component fatigue resistance .37
8 Analysis . .40
8.1 General . 40
8.2 Analysis methods .41
8.3 Coupling effects .41
8.4 Environmental loads on the floating structure .42
8.4.1 General .42
8.4.2 Wave forces .42
8.4.3 Wind forces .42
8.4.4 Current forces and VIM .43
8.5 Environmental loads on mooring lines and risers .43
8.6 Mooring analysis for strength, offsets and clearances .43
8.6.1 Basic considerations .43
8.6.2 Extreme value statistics .43
8.6.3 Design values for responses to transient wind squalls . 44
8.6.4 Mitigating mooring line trenching effects on AHC . 44
8.7 Mooring analysis for fatigue. 44
8.7.1 Basic considerations . 44
8.7.2 Analysis approach . 44
8.7.3 Fatigue damage calculation methods .45
8.8 Response based analysis .47
9 Dynamic positioning and thruster-assisted mooring. 47
9.1 General .47
9.1.1 Dynamic positioning .47
9.1.2 Thruster assisted mooring. 48
9.2 DP and TAM equipment classes . 48
9.3 Available effective thrust . 49
9.4 Determination of allowable thrust . 49
9.5 Load sharing of TAM system . 49
9.5.1 General . 49
iv
ISO 19901-7:2026(en)
9.5.2 Mean load reduction method . 49
9.5.3 Weathervaning structures . 50
9.5.4 System dynamic analysis . 50
9.6 Failure mode and effects analysis . 50
9.7 Design, test and maintenance .51
9.8 Operating personnel .51
9.9 Determination of stationkeeping capability .51
10 Installation, test load and as-installed survey . 51
10.1 General .51
10.2 Installation considerations and storm-safe criteria .52
10.3 Mooring line handling and installation procedure .52
10.4 Test loading requirements . 53
10.4.1 General . 53
10.4.2 Anchor test load for permanent mooring systems . 53
10.4.3 Anchor test load for mobile mooring systems . 53
10.5 Installation tolerances . 53
10.6 Traceability records . 54
10.7 As-installed survey and establishment of as-installed capacity . 54
11 Integrity management, survey and inspection, and monitoring .55
11.1 Integrity management . 55
11.2 Surveys and inspections . 55
11.2.1 In-service inspection program . 55
11.2.2 As-built inspection . 55
11.2.3 Annual survey . 55
11.2.4 5-year survey . 56
11.3 Conformity assessment .57
11.4 Monitoring . 58
11.4.1 Position and heading monitoring . 58
11.4.2 Line failure detection . 58
Annex A (informative) Additional information and guidance .59
Annex B (normative) Regional requirements and supporting information .140
Bibliography .185
v
ISO 19901-7:2026(en)
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
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This document was prepared by Technical Committee ISO/TC 67, Oil and gas industries including lower
carbon energy, Subcommittee SC 7, Offshore structures, in collaboration with the European Committee for
Standardization (CEN) Technical Committee CEN/TC 12, Oil and gas industries including lower carbon energy,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 19901-7:2013), which has been technically
revised.
The main changes are as follows:
— addition of requirements for a mooring integrity management system;
— emphasis on the definition of the operator's expectations on the performance standard;
— inclusion of fibre ropes as a standard material such as chain and steel wire ropes;
— alignment of text relating to the geotechnical design of anchors with ISO 19901-4;
— inclusion of guidance on OPB (out of plane bending) fatigue and squall design cases.
A list of all parts in the ISO 19901 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 19901-7:2026(en)
Introduction
The International Standards on offshore structures prepared by TC 67 (i.e. ISO 19900, the ISO 19901 series,
ISO 19902, ISO 19903, ISO 19904-1, the ISO 19905 series, ISO 19906) constitute a common basis covering
those aspects that address design requirements and assessments of offshore structures used by the oil and
gas industries worldwide. The intention in their application is to achieve reliability levels appropriate for
manned and unmanned offshore structures, irrespective type of structure and the nature or combination of
materials used.
It is important to recognize that structural integrity is a concept comprised of models that describe 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 design or structural system. The implications
involved in modifications therefore should be considered in relation to the overall reliability of all offshore
structural systems.
The International Standards on offshore structures prepared by TC 67 are intended to provide a wide
breadth of choice for structural configurations, materials and techniques without hindering innovation.
Informed engineering judgement is therefore necessary in the use of these International Standards.
This document 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 energy production platforms (with and without storage) 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 and flotels) and construction units (such as heavy lift vessels and
pipelay units).
This document assumes that permanently moored hydrocarbon production systems that are equipped
with stationkeeping systems as a minimum have the ability to both shut-in wells and the facility in case of
emergency (e.g. emergency shut-down valves on the seabed), otherwise the consequence of mooring failure
can be significantly different.
Stationkeeping is a generic term covering systems for keeping a floating structure, which is under the
constant influence of external actions, either at a pre-defined location or at a pre-defined heading or both
with limited excursions. Stationkeeping systems resist external actions by means of any of the following:
— mooring systems (e.g. spread mooring systems or single point mooring systems);
— dynamic positioning systems (generally consisting of thrusters)
— a combination of mooring system and thrusters (thruster assisted mooring systems).
The external actions generally consist of wind, wave, current and ice actions on the floating structure,
mooring and risers.
The procedures for the design of permanent or site-specific assessment of mobile mooring systems specified
in this document are based on a deterministic approach where mooring system responses (such as line
tensions, vessel offsets, and anchor loads) are evaluated for a design environment defined by an annual
probability of exceedance or return period. Mooring system responses are then checked against specified
requirements for mooring strength, offsets and orientation, clearances, anchor capacity, fatigue resistance,
etc. The minimum specified requirements are defined either in this document or by the operator if more
stringent.
NOTE Stationkeeping systems designed based on this deterministic approach can have differing levels of
reliability.
For moored structures (vessels), system responses are calculated and compared to minimum specified
requirements for:
— Ultimate limit states (ULS): mooring component strength. Vessel offset, orientation, and clearance
constraints. Herein the ULS includes both intact and single failure condition for stationkeeping systems.
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ISO 19901-7:2026(en)
— Serviceability limit states (SLS): vessel offset, orientation, and clearance constraints. For mooring
components this includes clearances with the vessel, risers, umbilicals, seabed, water surface, field
infrastructure, exclusion zones, etc.
— Fatigue limit states (FLS) : cumulative mooring component fatigue damage.
— Accidental and abnormal limit state (ALS): no criteria are given for accidental or abnormal limit state
which are left to operator decision or local authorities requirements.
The methodology described in this document identifies a set of coherent analysis techniques 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 specified in this document.
Descriptions of characteristics and typical components found in these systems are given in Annex A.
Some background to, and guidance on, the use of this document is provided in Annex A. The clause numbering
in Annex A is the same as in the main text to facilitate cross-referencing.
Regional information, where available, is provided in Annex B.
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International Standard ISO 19901-7:2026(en)
Specific requirements for offshore structures —
Part 7:
Stationkeeping systems for floating offshore structures and
mobile offshore units
1 Scope
This document specifies methodologies for:
a) the design, analysis and evaluation of stationkeeping systems for floating offshore structures;
b) the assessment of stationkeeping systems for site-specific applications of mobile offshore units and
construction units.
Originally developed for floating structures used in the oil and gas industry, this document is now also used
in the renewable energy sector. The extent of application of this document to floating structures used in
other industries is at the discretion of the relevant standard entity and its users. For example, IEC 61400-3-2
for floating wind applies this document to determine stationkeeping system responses while incorporating
its own load conditions, safety factors, and environmental return periods.
This document is applicable to the following types of stationkeeping systems, which are either covered
directly in this document or through reference to other guidelines:
— spread mooring syste
...