IEC TS 62600-10:2021

IEC TS 62600-10 ®
Edition 2.0 2021-07
TECHNICAL
SPECIFICATION
colour
inside
Marine energy – Wave, tidal and other water current converters –
Part 10: Assessment of mooring system for marine energy converters (MECs)
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IEC TS 62600-10 ®
Edition 2.0 2021-07
TECHNICAL
SPECIFICATION
colour
inside
Marine energy – Wave, tidal and other water current converters –

Part 10: Assessment of mooring system for marine energy converters (MECs)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.140 ISBN 978-2-8322-1001-5

– 2 – IEC TS 62600-10:2021 © IEC 2021
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references. 9
3 Terms and definitions . 9
4 Abbreviated terms . 10
5 Principal elements . 10
5.1 General . 10
5.2 Technology qualification . 10
5.3 Safety and risk consideration . 11
5.4 Safety levels . 11
5.5 Design procedure . 11
5.6 Inspection and maintenance requirements . 11
6 Environmental and site conditions . 11
6.1 General . 11
6.2 Primary environmental conditions . 12
6.3 Secondary environmental conditions . 12
6.3.1 General . 12
6.3.2 Marine growth . 12
6.3.3 Seabed conditions . 12
6.4 Site characteristics . 12
6.4.1 General . 12
6.4.2 Environmentally sensitive and protected areas and marine animals . 12
6.4.3 Nearshore impact . 12
6.4.4 Vandalism and misuse . 13
6.4.5 Marine traffic . 13
6.4.6 Shallow water conditions . 13
7 Design load cases . 13
7.1 General . 13
7.2 Analysis procedure overview . 13
7.3 Load categories . 14
7.3.1 General . 14
7.3.2 Dynamic analysis of MEC response to environmental conditions . 15
7.3.3 Low frequency loads . 15
7.3.4 Wave frequency loads on mooring components . 15
7.3.5 Wave frequency loads on MEC . 15
7.3.6 High frequency loading . 16
7.4 Interaction with waves, currents, wind, water level and ice . 16
7.4.1 General . 16
7.4.2 Resonant response . 17
7.4.3 Design return period for short term deployments . 17
7.5 Mooring line components . 17
7.5.1 General . 17
7.5.2 Component strength . 17
7.5.3 Component fatigue life . 18

7.5.4 Redundancy . 18
7.5.5 Clearance . 18
7.6 Umbilical considerations . 18
7.6.1 Umbilical response . 18
7.6.2 Umbilical strength . 18
7.6.3 Umbilical offset and clearance limits . 18
7.7 Limit states . 19
7.7.1 General . 19
7.7.2 Ultimate limit state (ULS) . 19
7.7.3 Accidental limit state (ALS) . 19
7.7.4 Serviceability limit state (SLS) . 19
7.7.5 Fatigue limit state (FLS) . 19
7.7.6 Consequence class safety factors . 20
7.7.7 Mooring component failure . 20
7.7.8 Anchor holding capacity . 20
7.7.9 Load case modelling and simulation . 21
7.7.10 Design conditions . 22
8 In-service inspection, monitoring, testing, and maintenance . 32
8.1 General . 32
8.2 Anchor proof loading . 33
8.3 Component replacement . 33
8.3.1 General . 33
8.3.2 Fibre rope component inspection and replacement . 33
8.3.3 Inspection and predictive procedures . 33
8.4 In air and splash zone mooring line sections . 34
8.5 Submerged mooring line sections . 34
8.6 Commissioning and decommissioning procedures . 35
Annex A (informative) Moorings and anchoring systems . 36
A.1 Types of moorings and anchoring systems . 36
A.1.1 General . 36
A.1.2 Mooring systems . 36
A.2 Mooring line components . 38
A.2.1 General . 38
A.2.2 Chain . 38
A.2.3 Wire rope . 39
A.2.4 Synthetic rope . 39
A.2.5 Elastic tethers . 46
A.2.6 Clump weights . 47
A.2.7 Buoyancy aids . 47
A.2.8 Connectors and accessories . 47
A.3 Anchors . 48
A.3.1 General . 48
A.3.2 Drag embedment anchor . 48
A.3.3 Pile anchor . 49
A.3.4 Suction anchor . 49
A.3.5 Gravity installed anchor . 50
A.3.6 Gravity anchor . 51
A.3.7 Plate anchor . 52
A.3.8 Screw and rock anchors . 52

– 4 – IEC TS 62600-10:2021 © IEC 2021
A.3.9 Type selection . 53
A.3.10 Holding capacity . 53
A.3.11 Sediment and rock conditions . 54
A.3.12 Fluke setting . 54
A.3.13 Installation . 54
A.3.14 Proof loading . 55
A.3.15 Directional anchor loading . 55
A.3.16 Failure mode . 55
A.3.17 Environmental loading . 55
A.3.18 Failure point . 55
Annex B (normative) Safety and risk considerations . 56
B.1 General . 56
B.2 Risk . 56
B.2.1 General . 56
B.2.2 Definition . 56
B.2.3 Consequence types . 56
B.3 Risk assessment methodology . 57
B.3.1 General . 57
B.3.2 Methodology flowchart . 57
B.4 Consequence considerations for mooring failure . 59
B.5 Consequence classification . 59
B.5.1 General . 59
B.5.2 Consequence impact considerations . 60
B.5.3 Risk mitigation considerations . 61
B.5.4 Risk acceptance . 61
Annex C (informative) Numerical modelling considerations . 63
C.1 General . 63
C.2 Mooring, umbilical, and dynamic cable models . 63
C.2.1 General . 63
C.2.2 Static and catenary models . 63
C.2.3 Discrete models . 63
C.2.4 Floating unit numerical models . 63
Bibliography . 65

Figure 1 – Recommended conceptual mooring analysis procedure . 14
Figure A.1 – Spread mooring configuration . 36
Figure A.2 – Catenary anchor leg mooring configuration . 37
Figure A.3 – Single anchor leg mooring configuration . 37
Figure A.4 – Turret mooring configuration . 38
Figure A.5 – Studless and studlink chain . 38
Figure A.6 – Typical wire rope construction . 39
Figure A.7 – Parallel yarn rope . 41
Figure A.8 – Parallel core rope . 41
Figure A.9 – Rope construction with 18+12+6+1 format . 42
Figure A.10 – Three strand laid construction . 42
Figure A.11 – Rope with 8 plait braid construction . 43
Figure A.12 – Rope with braid on braid construction . 43

Figure A.13 – Types of connectors . 48
Figure A.14 – Drag embedment anchor . 49
Figure A.15 – Pile anchor . 49
Figure A.16 – Suction anchor . 50
Figure A.17 – Gravity installed torpedo anchor . 51
Figure A.18 – Gravity installed anchor with rotating load arm . 51
Figure A.19 – Gravity anchor. 52
Figure A.20 – Suction or pile driven plate anchor . 52
Figure A.21 – Screw anchor . 53
Figure A.22 – Rock anchor . 53
Figure B.1 – General risk methodology flowchart . 58

Table 1 – Potential nearshore impacts . 13
Table 2 – Combinations of uncorrelated extreme events . 17
Table 3 – Consequence class associated safety factors for dynamic analysis
techniques . 20
Table 4 – Safety factors for holding capacity of drag anchors . 21
Table 5 – Safety factors for holding capacity of anchor piles and suction piles . 21
Table 6 – Safety factors for holding capacity of gravity and plate anchors . 21
Table 7 – Design load cases for WECs . 24
Table 8 – Design load cases for CECs . 26
Table A.1 – Generalized comparison of mooring line material characteristics . 40
Table A.2 – Properties for selection of synthetic fibre . 44
Table A.3 – Generalized comparison of common rope relevant material properties . 44
Table B.1 – Consequence categories . 59

– 6 – IEC TS 62600-10:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MARINE ENERGY –
WAVE, TIDAL AND OTHER WATER CURRENT CONVERTERS –

Part 10: Assessment of mooring system
for marine energy converters (MECs)

FOREWORD
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IEC TS 62600-10 has been prepared by IEC technical committee 114: Marine energy – Wave,
tidal and other water current converters. It is a Technical Specification.
This second edition cancels and replaces the first edition published in 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Added specific Design Load Cases in alignment with 62600-2.
b) Added additional robustness check requirements.
c) Rearranged document for ease of use and alignment with 62600-2.
d) Added additional informative clauses on mooring materials.

The text of this Technical Specification is based on the following documents:
Draft Report on voting
114/390/DTS 114/395/RVDTS
114/395A/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
A list of all parts in the IEC 62600 series, published under the general title Marine energy –
Wave, tidal and other water current converters, can be found on the IEC website.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 8 – IEC TS 62600-10:2021 © IEC 2021
INTRODUCTION
This document defines rules and assessment procedures for the design, installation and
maintenance of mooring system with respect to technical requirements for floating marine
energy converters.
The proposed work aims to bring together expert knowledge from the marine energy power and
offshore engineering industries in order to formulate a guideline specification of the design,
installation and maintenance requirements for mooring system of floating Marine Energy
Converters.
In addition to safety and ocean environmental requirements, this document focuses on the
strength requirements of mooring systems for Marine Energy Converters.

MARINE ENERGY –
WAVE, TIDAL AND OTHER WATER CURRENT CONVERTERS –

Part 10: Assessment of mooring system
for marine energy converters (MECs)

1 Scope
The purpose of this document is to provide uniform methodologies for the design and
assessment of mooring systems for floating Marine Energy Converters (MECs) (as defined in
the TC 114 scope). It is intended to be applied at various stages, from mooring system
assessment to design, installation and maintenance of floating Marine Energy Converters plants.
This document is applicable to mooring systems for floating Marine Energy Converters units of
any size or type in any open water conditions. Some aspects of the mooring system design
process are more detailed in existing and well-established mooring standards. The intent of this
document is to highlight the different requirements of Marine Energy Converters and not
duplicate existing standards or processes.
While requirements for anchor holding capacity are indicated, detailed geotechnical analysis
and design of anchors are beyond the scope of this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
IEC TS 62600-1: 2020, Marine energy – Wave, tidal and other water current converters – Part
1: Vocabulary
IEC TS 62600-2:2019, Marine energy - Wave, tidal and other water current converters - Part 2:
Marine energy systems - Design requirements
IEC TS 62600-4:2020, Marine energy – Wave, tidal and other water current converters – Part 4:
Specification for establishing qualification of new technology
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 62600-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

– 10 – IEC TS 62600-10:2021 © IEC 2021
4 Abbreviated terms
ALARP As low as reasonably practicable
ALS Accidental limit state
API American Petroleum Institute
CALM Catenary anchor leg mooring
CEC Current Energy Converter
CFD Computational fluid dynamics
DP  Dynamic positioning
FLS Fatigue limit state
HAZID Hazard Identification
HHP High holding power
IEC International Electrotechnical Commission
ISO  International Organisation for Standardisation
LTM Long term mooring
MBL Minimum breaking load
MEC Marine energy converter
MEP Marine environmental protection
MPM Most probable maximum
PTO Power take-off
PT  Project team
ROV Remotely operated vehicle
SALM Single anchor leg mooring
SF  Safety factor
SLS  Serviceability limit state
SPM Single point mooring
TEC Tidal Energy Converter
ULS  Ultimate limit state
UV  Ultraviolet
VIM  Vortex induced motion
VIV  Vortex induced vibration
WEC Wave Energy Converter
5 Principal elements
5.1 General
The engineering and technical requirements to ensure integrity of a mooring system for a MEC
are given in this document. This document is used in conjunction with IEC TS 62600-2.
5.2 Technology qualification
Technology qualification for mooring system components shall be completed in accordance with
IEC TS 62600-4.
5.3 Safety and risk consideration
Understanding risk factors is important in quantifying the consequence class of the mooring
design. The consequence class dictates the required level of safety of the mooring design. A
mooring related risk assessment shall be completed. Guidelines for a mooring related risk
assessment is discussed in more detail in Annex B. Additional guidelines for risk assessment
can be found in IEC TS 62600-2:2019,5.4 and IEC TS 62600-4.
5.4 Safety levels
The assessment of consequences of failure shall cover all phases of MEC installation, operation,
maintenance, and decommissioning, where the mooring system is affected or affects the overall
system. Related consequences shall consider:
• Risk to life and injury
• Environmental impact
• Economic consequences
• Loss of public reputation and other political and societal consequences
-4
The requirements in this document, including safety factors are intended to comply with 10
per year probability of failure for normal consequence class. This is in alignment with the
objective of IEC TS 62600-2. However, a more conservative consequence class is provided
along with associated safety factors that may be applicable for a smaller associated target
probability of failure.
Where the risk can be controlled by short term deployments, or other factors, particularly for
prototype deployments, a larger probability of failure may be tolerated. More information and
guidance on safety and risk considerations can be found in Annex B.
5.5 Design procedure
The design process is iterative in nature. The potentially complex nature of MEC dynamic
behaviour and external loading effects mean that careful consideration of the definition of
environmental conditions, specific design load cases in the limit states required, and the
limitations of analysis techniques used should be made. Guidance on environmental and site
conditions are described in Clause 6.
The MEC mooring system design shall be regarded as completed when the integrity is verified
by the limit state analysis described in Clause 7.
5.6 Inspection and maintenance requirements
The integrity of a station keeping system and its serviceability throughout the design service
life are not only strongly dependent on a competent design, but also on the quality control
exercised in manufacture, supervision on-site, handling during transport and installation, and
the manner in which the system is used and maintained. Further information on inspection and
maintenance requirements are described in Clause 8.
6 Environmental and site conditions
6.1 General
External conditions include metocean and other environmental factors that will vary based on
location and should be considered on a site specific basis.

– 12 – IEC TS 62600-10:2021 © IEC 2021
6.2 Primary environmental conditions
The environmental conditions described in 6.2 of IEC TS 62600-2:2019 shall be considered in
the modelling, analysis, and prediction of environmental loads on and resulting dynamic
response of MECs for the purpose of resolving the mooring design. The return periods for
combinations of environmental conditions listed in 7.4 shall be used and are intended to align
with IEC TS 62600-2:2019.
Wind, wave, current, water elevation variations, snow and ice, and other conditions at each site
shall be considered. Guidelines for determining metocean conditions can be found in
ISO 19901-1. Annex A.5.7 of ISO 19901-1:2005 provides guidance to establish metocean
conditions with larger return periods. The confidence interval of statistical extrapolations to
establish return periods from measured site specific data can have a significant effect on the
return period values and should be selected carefully.
The return period of metocean conditions in the design load cases are a minimum. The
sensitivity to the system response to return period can be considered.
6.3 Secondary environmental conditions
6.3.1 General
Secondary environmental conditions listed in 6.3 of IEC TS 62600-2:2019 shall be considered
when the potential exists for significant effects on the MEC and mooring at the deployment site.
6.3.2 Marine growth
The type and accumulation rate of marine growth at a specific site can affect mass and
hydrodynamic properties and therefore the dynamic response of the MEC and mooring lines.
This shall be taken into consideration for mooring systems designed without any regular marine
growth removal or protection plan. Indicative marine growth rates for a variety of locations can
be found in ISO 19901-1. Increased line weight and drag coefficients representative of site-
specific marine growth accumulation profiles should be considered.
6.3.3 Seabed conditions
Seabed conditions and type are required for anchor selection. More information on anchor
selection can be seen in Annex C.
6.4 Site characteristics
6.4.1 General
Characteristics of the deployment site location may have special considerations that may
directly affect the mooring design through various requirements or component selection.
6.4.2 Environmentally sensitive and protected areas and marine animals
Selected sites for MECs can be located near sensitive or protected habitats. Any device located
in such a habitat can impact the ecology and environment via direct contact or indirectly by
harassment. Mooring systems can have impact without a failure event. Consequences can
include reduction in water quality from sediment churn and bottom scour due to normal mooring
motion, marine life entanglement with mooring components, and habitat damage from anchor
placement and installation activities. In addition, noise produced by strum, mooring line
interaction with the seabed, and mooring component rattle can be considered harassment.
6.4.3 Nearshore impact
Nearshore impact is defined as impacts associated with any developmental activities related to
the installation or operation of MECs that can take place in the area between the shoreline and

the area defined as the offshore zone. Nearshore impacts can have unintended consequences
that can be financial, environmental, or societal. Nearshore impacts may include but are not
limited to the following, listed in Table 1.
Table 1 – Potential nearshore impacts
Impact type Description of impact
Noise Noise generated during installation, recovery, or other
operations involving the mooring system that can disturb
marine life
Proximity Dredging operations in coastal zones can disrupt MEC
moorings or umbilical systems
6.4.4 Vandalism and misuse
Vandalism is the deliberate defacement, destruction, or theft of an existing MEC mooring
system or mooring components. The misuse of floating structures as temporary tie-off buoys
for sport and commercial vessels is common in nearshore areas. Accessibility of mooring
components and connections should be considered.
6.4.5 Marine traffic
The type and frequency of other marine traffic traversing the site should be considered. For
example, local or commercial fishing vessels can accidentally entangle in the MEC mooring
system that could lead to failure. In addition, any restriction within the water column to mooring
line components with regards to safe keel clearance regardless of limit state shall be considered.
A notice to mariners should be filed with the applicable regional authority and nautical charts
updated to reflect the location of the MEC and associated moorings.
6.4.6 Shallow water conditions
Synthetic ropes may contact the seabed during operations and installation if appropriately
designed. Synthetic ropes should use protective jacket designs that have been tested and
verified for specific conditions of sharp rocks or other features that could potentially cause
damage to the lines.
7 Design load cases
7.1 General
Each mooring design will be a function of the site specific environmental conditions and specific
MEC characteristics. Determining the mooring design that satisfies the limit states may not be
obvious and may require an iterative process. Static, quasi-static, and dynamic analysis
procedures can apply in the process.
The following subclauses elaborate on specific considerations for mooring design for MECs as
well as clarifying analysis procedures and load cases.
7.2 Analysis procedure overview
The various limit states, ULS, ALS, FLS, and SLS, and associated load cases define the
minimum set of criteria the mooring design shall satisfy. A recommended analysis procedure is
summarized by the flow chart seen in Figure 1. This is the recommended procedure but is not
necessarily the procedure that shall be used for design. This procedure is based on similar
processes presented in IEC TS 62600-2:2019 and ISO 19901-7:2013. This procedure can be
summarized as follows:
a) Determine site specific metocean and external conditions for the location.

– 14 – IEC TS 62600-10:2021 © IEC 2021
b) Establish a conceptual mooring pattern. Properties of the mooring components shall be
established. Mooring pretension should be considered including impacts due to water level
variations and achievable installation tolerance.
c) Determine external loads on the mooring and MEC due to metocean and external conditions.
d) Complete an analytical or static analysis using mean environmental loading to allow rapid
initial iteration on mooring components, pretensions, and mooring envelope. Iterate and
modify the mooring design as needed.
e) Perform a dynamic analysis on the mooring system for each of the limit states considered.
f) If the resulting design criteria for any limit state are not satisfied, iterate on the mooring
design concept or restart the process with a new mooring design concept.

Figure 1 – Recommended conceptual mooring analysis procedure
7.3 Load categories
7.3.1 General
Environmental loads listed in IEC TS 62600-2:2019,7.2, and the effects described in this clause,
shall be considered, unless they can be shown to have either no significant effect or are not
applicable to the deployment site, in assessing the combined MEC system and mooring
response. Further discussion on these environmental load types are discussed here. A range
of possible combined loads may result:
a) Low frequency current, wind and wave drift loads.
b) Wave frequency loading.
c) High frequency VIV, seismic, PTO, ice and ship impact.
The combined assorted loadings, including those from winds, currents, and waves, on the MEC
and mooring system are required to determine the motion response and mooring loads. The
assorted loadings may be determined by relevant analytical, numerical, or experimental
methods. Some loading can only be determined through the use of experimental methods or
specialized software. Interaction between and directionality of wind, current, and waves shall
be examined.
7.3.2 Dynamic analysis of MEC response to environmental conditions
In comparison to static and quasi-static modelling, dynamic modelling considers the
acceleration and velocity of all components in the system. Inertia, damping, and stiffness of the
MEC and mooring as well as PTO effects may be incorporated in the dynamic model. Dynamic
modelling may be coupled or uncoupled and performed in the frequency domain or the time
domain. Time domain modelling is t
...