IEC TS 62600-10:2015

IEC TS 62600-10 ®
Edition 1.0 2015-03
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 1.0 2015-03
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 978-2-8322-2431-1

– 2 – IEC TS 62600-10:2015 © IEC 2015
CONTENTS
FOREWORD. 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 9
4 Abbreviated terms . 11
5 Principal element . 12
5.1 General . 12
5.2 Mooring and anchor systems . 12
5.3 Design considerations . 12
5.4 Safety and risk consideration . 13
5.5 Analysis procedure . 13
5.6 Inspection and maintenance requirements . 13
6 Types of moorings and anchoring systems . 13
6.1 General . 13
6.2 Mooring systems . 13
6.2.1 General . 13
6.2.2 Spread moorings (catenary, taut-line and semi-taut-line) . 13
6.2.3 Single point moorings (SPM) . 14
6.3 Mooring line components . 15
6.3.1 General . 15
6.3.2 Chain . 15
6.3.3 Wire rope . 16
6.3.4 Synthetic rope . 17
6.3.5 Clump weights . 17
6.3.6 Buoyancy aids . 17
6.3.7 Connectors and accessories . 17
6.4 Anchors types . 18
6.4.1 General . 18
6.4.2 Drag embedment anchor . 18
6.4.3 Pile anchor . 19
6.4.4 Suction anchor . 19
6.4.5 Gravity installed anchor . 20
6.4.6 Gravity anchor . 20
6.4.7 Plate anchor . 21
6.4.8 Screw anchor . 21
7 Design consideration . 22
7.1 General . 22
7.2 Limit states . 22
7.2.1 Ultimate limit state (ULS) . 22
7.2.2 Accidental limit state (ALS) . 22
7.2.3 Serviceability limit state (SLS) . 22
7.2.4 Fatigue limit state (FLS) . 22
7.3 External conditions . 23
7.3.1 General . 23
7.3.2 Metocean conditions . 23

7.3.3 Marine growth . 23
7.3.4 Marine life . 23
7.3.5 Environmentally sensitive and protected areas and marine animals . 23
7.3.6 Nearshore impact . 23
7.3.7 Vandalism and misuse . 23
7.3.8 Marine traffic . 24
7.4 Assorted loading . 24
7.4.1 General . 24
7.4.2 Low frequency loads . 24
7.4.3 Wave frequency loads on mooring components . 24
7.4.4 Wave frequency loads on MEC . 25
7.4.5 High frequency loading . 25
7.5 Mooring line components . 25
7.5.1 Component strength . 25
7.5.2 Component fatigue life . 25
7.5.3 Redundancy . 25
7.5.4 Clearance . 25
7.6 Umbilical considerations . 26
7.6.1 Umbilical response . 26
7.6.2 Umbilical strength . 26
7.6.3 Umbilical offset and clearance limits . 26
7.7 Anchors . 26
7.7.1 Type selection . 26
7.7.2 Holding capacity . 26
7.7.3 Sediment and rock conditions . 26
7.7.4 Fluke setting . 27
7.7.5 Installation . 27
7.7.6 Proof loading . 27
7.7.7 Directional anchor loading . 27
7.7.8 Failure mode . 27
7.7.9 Environmental loading . 27
8 Safety and risk considerations . 27
8.1 Overview . 27
8.2 Risk . 27
8.2.1 General . 27
8.2.2 Definition . 28
8.2.3 Consequence types . 28
8.2.4 General risk mitigation . 28
8.2.5 ALARP principle . 28
8.3 Risk assessment methodology . 28
8.3.1 General . 28
8.3.2 Methodology flowchart . 29
8.3.3 Basic considerations . 30
8.3.4 Probability assessment . 31
8.3.5 Consequence classification assessment . 31
8.4 Consequence considerations for mooring failure . 31
8.5 Consequence classification . 31
8.5.1 General . 31
8.5.2 Consequence impact considerations . 32

– 4 – IEC TS 62600-10:2015 © IEC 2015
8.5.3 Waterway navigation impacts . 33
8.5.4 Environmentally sensitive and protected sites . 33
8.5.5 Archaeological sites . 33
8.6 Risk mitigation considerations . 33
8.6.1 Mitigation overview . 33
8.6.2 Probability reduction . 33
8.6.3 Consequence reduction . 33
8.7 Risk acceptance . 34
8.7.1 Acceptance overview . 34
8.7.2 Documentation . 34
9 Analysis procedure . 34
9.1 General . 34
9.2 Basic considerations . 34
9.3 Analysis procedure overview . 35
9.4 Modelling consideration . 36
9.4.1 General . 36
9.4.2 Mooring and umbilical models . 36
9.4.3 Floating unit numerical models . 36
9.4.4 Coupled and uncoupled analysis . 37
9.5 Analysis procedure considerations . 37
9.5.1 Metocean directionality . 37
9.5.2 Resonant response . 37
9.5.3 Dynamic mooring analysis . 37
9.5.4 Design situations of ULS . 38
9.5.5 Design situations of ALS . 38
9.5.6 Design situations of FLS . 38
9.5.7 Design situations of SLS . 38
9.6 Mooring design criteria . 38
9.6.1 Design return period . 38
9.6.2 Consequence class design factor . 38
9.6.3 Mooring line component failure . 39
9.6.4 Anchor holding capacity . 39
10 In-service inspection, monitoring, testing, and maintenance . 40
10.1 General . 40
10.2 Mooring system proof loading . 41
10.3 Component replacement . 41
10.4 In air and splash zone mooring line sections . 41
10.5 Submerged mooring line sections . 41
10.6 Commissioning and decommissioning procedures . 42
Annex A (informative) Sample mooring design . 43
A.1 General . 43
A.2 Problem layout . 43
A.3 Consequence class identification . 44
A.4 Mooring design process . 47
Bibliography . 50

Figure 1 – Spread mooring configuration . 14
Figure 2 – Catenary anchor leg mooring configuration . 14

Figure 3 – Single anchor leg mooring configuration . 15
Figure 4 – Turret mooring configuration . 15
Figure 5 – Studless and studlink chain . 16
Figure 6 – Typical wire rope construction . 16
Figure 7 – Types of connectors . 18
Figure 8 – HHP drag embedment anchor . 19
Figure 9 – Pile anchor . 19
Figure 10 – Suction anchor . 20
Figure 11 – Gravity installed anchor . 20
Figure 12 – Gravity anchor . 21
Figure 13 – Plate anchor . 21
Figure 14 – Screw anchor . 22
Figure 15 – General risk methodology flowchart . 30
Figure 16 – Conceptual mooring analysis procedure . 35
Figure A.1 – Potential tidal current MEC installation locations A, B; artificial reef C;
fish farm D; marine traffic corridor E . 43
Figure A.2 – Mooring line component minimum ASF for each return period environment
5, 10, 20, 50, and 100 plotted to determine mooring ULS return period . 48
Figure A.3 – Anchor minimum ASF for each return period environment 5, 10, 20, 50,
and 100 plotted to determine anchor ULS return period . 48

Table 1 – Potential nearshore impacts . 23
Table 2 – Consequence categories . 31
Table 3 – Consequence class . 32
Table 4 – Consequence class associated design factors . 39
Table 5 – Safety factors for ULS and ALS conditions . 39
Table 6 – Safety factors for holding capacity of drag anchors factors . 40
Table 7 – Safety factors for holding capacity of anchor piles and suction piles . 40
Table 8 – Safety factors for holding capacity of gravity and plate anchors . 40
Table A.1 –Consequence classification matrix: location A . 45
Table A.2 – Consequence classification matrix: location B . 46

– 6 – IEC TS 62600-10:2015 © IEC 2015
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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The main task of IEC technical committees is to prepare International Standards. In
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• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 62600-10, which is a technical specification, has been prepared by IEC technical
committee 114: Marine energy – Wave, tidal and other water current converters.

The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
114/140/DTS 114/150A/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

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 62600-10:2015 © IEC 2015
INTRODUCTION
This technical specification 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 will aim 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 MECs.
In addition to safety and ocean environmental requirements, this technical specification
focuses on the strength requirements of mooring systems for MECs.

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 Technical Specification is to provide uniform methodologies for the design
and assessment of mooring systems for floating MECs (as defined in TC114 scope). It is
intended to be applied at various stages, from mooring system assessment to design,
installation and maintenance of floating MEC plants.
This technical specification is applicable to mooring systems for floating MEC 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 technical specification is to highlight the different requirements of MECs 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 technical specification.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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, Marine energy – Wave, tidal and other water current converters – Part 1:
Terminology
ISO 17776:2000, Petroleum and natural gas industries – Offshore production installations –
Guidelines on tools and techniques for hazard identification and risk assessment
ISO 19901-1:2005, Petroleum and natural gas industries – Specific requirements for offshore
structures – Part 1: Metocean design and operating considerations
ISO 19901-7:2013, Petroleum and natural gas industries – Specific requirements for offshore
structures – Part 7: Stationkeeping systems for floating offshore structures and mobile
offshore units
API RP 2SK, Design and Analysis of Station keeping Systems for Floating Structures, 3rd
Edition, October 2005
API RP 2I, In-Service Inspection of Mooring Hardware for Floating Structures, 3rd Edition,
3 Terms and definitions
For the purposes of this document, the following terms and definitions as well as those given
in IEC TS 62600-1 apply.
– 10 – IEC TS 62600-10:2015 © IEC 2015
3.1
anchor
device that provides a holding point at the seabed for a mooring line connected to a floating
MEC
3.2
catenary mooring
mooring system where restoring forces are provided by the distributed weight of mooring lines
3.3
connectors and accessories
hardware used to join various components in the mooring system not including the structures
fixed to the MEC or the anchor
3.4
design criteria
quantitative formulations that describe the conditions to be satisfied with each limit state
3.5
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
3.6
design limit
set of physical conditions during a certain reference period for which the structure member
will demonstrate that relevant limit states are not exceeded
3.7
dynamic response
acceleration and resulting motion of a MEC with mooring system as it is subject to assorted
loads
3.8
floating device
structure supported by buoyancy
3.9
limit state
condition for which a system or a component is at its limit of performance of its intended
function
3.10
mobile mooring
temporary anchoring arrangement at a specific location for a short period of time
3.11
mooring components
general class of devices and hardware used in the mooring of floating structures
3.12
mooring line
string of components connecting a MEC to an anchor
3.13
mooring system
compliant configuration that consists of mooring lines, components, and anchors

3.14
resistance
capacity to withstand loads and motions
3.15
return period
inverse of the annual probability
3.16
single point mooring
mooring system that consists of a single connection point to the MEC
3.17
spread mooring
mooring system that consists of multiple connection points to the MEC
3.18
stiffness
ratio of change in restoring forces to change in displacement
3.19
semi-taut mooring
mooring system comprised of attributes of both taut and catenary forms
3.20
taut-line mooring
mooring system where the restoring action is provided by elastic deformation of mooring lines
3.21
axisymmetric
floating structure that is symmetric about an axis of rotation
3.22
umbilical
compliant and slender structure that is used to transport fluid, electricity, data, or other
material from a MEC to another location
3.23
proof loading
test procedure that applies loads at some fraction of design load to confirm adequate
structural response
3.24
consequence class
classification that correlates to the potential for damage in the event of failure with an
associated set of design factors
3.25
design factor
factors that amplify loading and stresses that are used to compensate for uncertainty and the
potential for damage in the event of failure in accordance with the associated consequence
class
4 Abbreviated terms
ALARP As low as reasonably practicable
ALS Accidental limit state
– 12 – IEC TS 62600-10:2015 © IEC 2015
API American Petroleum Institute
ASF Adjusted safety factor
CALM Catenary anchor leg mooring
CFD Computational fluid dynamics
DP Dynamic positioning
DF Design factor
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
ULS Ultimate limit state
UV Ultraviolet
VIM Vortex induced motion
VIV Vortex induced vibration
5 Principal element
5.1 General
This clause provides an overview of the content of this technical specification.
5.2 Mooring and anchor systems
An overview of existing mooring designs, components, and anchors is provided for reference.
5.3 Design considerations
Understanding the design inputs and limitations shall be considered when designing a
mooring system and selecting anchor types for MECs. Fundamental design considerations
include limit state categories, metocean and external conditions, external load effects, and
mooring line component and anchor hardware related considerations.

5.4 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.
5.5 Analysis procedure
The limit states influence the mooring design process. The potentially complex nature of MEC
dynamic behaviour and external loading effects mean that careful consideration of the
limitations of analysis techniques shall be made.
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.
6 Types of moorings and anchoring systems
6.1 General
This clause provides an overview of mooring and anchor types that may be used with floating
MECs. Floating structure station keeping systems vary depending on the characteristics of the
structure and on the environmental conditions. Single point moorings are frequently used for
floating structures where greater freedom in motion is required, while spread moorings are
used mostly on structures when maintaining a particular orientation is important. Another type
of station keeping system is dynamic positioning (DP). Dynamic positioning uses actively
controlled thrusters as part of the station keeping capability. Thruster-assisted moorings can
be used to reduce mooring line tensions or to control heading.
The mooring components, anchor types, and sizing depend on the site requirements, design,
and MEC power capture considerations.
6.2 Mooring systems
6.2.1 General
Examples of existing mooring system types for floating structures are described in the
following subclauses. These examples are not exhaustive.
6.2.2 Spread moorings (catenary, taut-line and semi-taut-line)
Spread moorings are often used when weathervaning, or rotation movement of a floating
structure such that it aligns to a wind or current load so as to minimize drag loading, is not
desirable. Spread moorings can incorporate chain, wire rope, synthetic rope, or various
combinations of materials. Spread mooring systems may use taut, semi-taut, or catenary
systems. A spread moored configuration can be seen in Figure 1.

– 14 – IEC TS 62600-10:2015 © IEC 2015

IEC
Figure 1 – Spread mooring configuration
6.2.3 Single point moorings (SPM)
Single point moorings allow floating structures to weathervane. A floating structure may
directly connect to the mooring system or to an intermediary moored buoy. There is wide
variety in the design of single point moorings but they all essentially perform the same
function. Examples of typical single point mooring systems are described below.
a) Catenary anchor leg mooring (CALM)
A CALM system consists of a large buoy that supports a number of catenary mooring lines.
The floating structure is connected to the buoy by a single connection point as indicated in
Figure 2.
IEC
Figure 2 – Catenary anchor leg mooring configuration
b) Single anchor leg mooring (SALM)
A SALM system consists of a large buoy that supports a single taut vertical mooring line. The
buoy floatation induces tensions that tend to restore the buoy to the vertical position. The
floating structure is connected to the buoy by a single connection point as indicated in
Figure 3.
IEC
Figure 3 – Single anchor leg mooring configuration
c) Turret mooring
A turret mooring system consists of lines that are attached as in a CALM or SALM buoy
system. The turret is attached to the floating structure via a bearing joint or other linkage that
allows relative yaw motion as indicated in Figure 4.
IEC
Figure 4 – Turret mooring configuration
6.3 Mooring line components
6.3.1 General
Mooring lines for floating structures are usually made up of wire rope, chain, synthetic fibre
rope or a combination thereof. Many possible combinations of line type, size and location, and
size of clump weights or buoys can be used to achieve the required mooring performance.
The following subclauses provide an illustration of common mooring components.
The selection of mooring components shall be based on design objectives. The mooring
components should meet material, manufacture, and testing requirements specified in
applicable certification rules. Mooring component properties (e.g. MBL, weight, etc.) shall be
based on manufacturer specific data. An adequate inspection and maintenance program shall
be developed to monitor for loss of integrity in-service. The components suitability for mobile
or long term mooring (LTM) deployments shall be considered. More information on aspects of
component selection can be found in A.1.7 and A.11.1 of ISO 19901-7:2013.
6.3.2 Chain
Chain size is defined by the bar diameter of the chain links. Diagrams of studless and studlink
chain can be seen in Figure 5. Various grades of chain are available from U-grades (normally
used for ship chain) to the higher grade of ORQ, R3, R3S, R4, R4S, and R5.

– 16 – IEC TS 62600-10:2015 © IEC 2015
Link Stud footprint
Stud weld
Stud
Flash weld
Link
Studless chain Stud chain
IEC
Figure 5 – Studless and studlink chain
The length of chain links have been standardised with an overall length of 6 times the nominal
bar diameter and 3,6 and 3,35 times the bar diameter for overall width for studded and
studless chain, respectively. To facilitate connection to other items, both chain types are often
terminated in slightly larger end links which are matched to LTM shackle designs.
When selecting chain, the choice of studded versus studless can be a key aspect. While
studded has greater fatigue life, a lost, damaged, or misaligned stud can reduce fatigue life to
less than that of studless chain. Studless chain can be easier to handle compared to studlink
since there is room in the link to attach a lifting point.
Corrosion allowance should be taken into account for LTM systems. Consideration of the
location of the system should be factored as it has been noted that the corrosion rate of chain
can be high in highly oxygenated environments. This corrosion will lead to a loss of strength
which shall be accounted for in the design.
6.3.3 Wire rope
Wire rope has a lower weight per unit length than chain, lower stiffness, and similar breaking
loads. Common wire ropes used in offshore mooring lines are six strand, spiral strand, and
multi-strand as seen in Figure 6. The wire rope is terminated with a socket for connection to
the other components in the mooring system. Special consideration is required to protect wire
rope components from coming in contact with the sea bed,
...