ISO 18821:2025

International
Standard
ISO 18821
First edition
Ships and marine technology —
2025-10
Marine combined connecting
mooring line
Navires et technologie maritime — Ligne d'amarrage
combinée marine
Reference number
© ISO 2025
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification, structure and code . 2
4.1 Classification .2
4.2 Structure .3
4.3 Codes .4
5 Design requirements . 4
5.1 General .4
5.2 Specifications .5
5.2.1 Steel wire rope used as mooring line .5
5.2.2 Synthetic fibre rope as mooring line .5
5.2.3 Connection device .6
5.2.4 Tails .6
5.2.5 Combined line .6
5.3 Designation .6
6 Test methods . 7
6.1 General .7
6.2 Surface quality .7
6.3 Dimensions .8
6.4 Linear density.8
6.5 Breaking force .8
6.6 Proof load and ultimate load .8
6.7 Cyclic loading and axial compression resistance .8
6.8 Immediate strain .8
6.9 Angled endurance .8
Annex A (informative) Specifications of mooring rope . 10
Annex B (informative) Specifications of connection devices .12
Annex C (informative) Tails specifications . 14
Annex D (informative) Specifications of combined lines .15
Annex E (informative) Proof load and ultimate load test of the connection devices.18
Annex F (informative) Example test report of combined line . 19
Bibliography .21

iii
Foreword
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iv
International Standard ISO 18821:2025(en)
Ships and marine technology — Marine combined connecting
mooring line
1 Scope
This document specifies the classification, structure and code, design requirements and testing methods of
a marine combined connecting mooring line (hereinafter referred to as a combined line), which consists of a
mooring line, connection device and tail.
This document applies to the design, manufacture and inspection of combined lines for tankers.
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.
ISO 1140, Fibre ropes — Polyamide — 3-, 4-, 8- and 12-strand ropes
ISO 1141, Fibre ropes — Polyester — 3-, 4-, 8- and 12-strand ropes
ISO 2307:2019, Fibre ropes — Determination of certain physical and mechanical properties
ISO 2408:2017, Steel wire ropes — Requirements
ISO 9554, Fibre ropes — General specifications
ISO 16143-1:2014, Stainless steels for general purposes — Part 1: Corrosion-resistant flat products
ISO 10325, Fibre ropes — High modulus polyethylene — 8-strand braided ropes, 12-strand braided ropes and
covered ropes
ISO 10556, Fibre ropes of polyester/polyolefin dual fibres
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
fibre rope
rope made from synthetic fibre
3.2
tail
short length of rope attached to the end of a mooring line to provide increased elasticity and also ease of
handling
3.3
cow hitch
method of joining two fibre ropes (3.1) without connection device
3.4
ship design minimum breaking load
ship design MBL
minimum breaking load of new, dry mooring lines for which a ship's mooring system is designed
Note 1 to entry: This minimum breaking load is expressed in kN.
3.5
line design break force
LDBF
minimum force at which a new, dry, spliced mooring line will break when tested
Note 1 to entry: This minimum force is expressed in kN.
3.6
tail design break force
TDBF
minimum force at which a new, wet, spliced tail will break when tested
Note 1 to entry: This minimum force is expressed in kN.
3.7
working load limit
WLL
maximum allowable load the mooring line is able to sustain
Note 1 to entry: This maximum allowable load is expressed in t.
3.8
proof load
force applied as a test to a finished connection device
Note 1 to entry: This force is expressed in kN.
3.9
ultimate load
maximum force reached during a static tensile test before the assembly being tested fails to retain the load
Note 1 to entry: This maximum force is expressed in kN.
3.10
safe working load
SWL
rated capacity of the connection device to withstand tensile force
4 Classification, structure and code
4.1 Classification
The combined lines can be classified into three types according to the way it can be connected. The three
types include T type, M type and C type. The code, type and content of combined line are shown in Table 1.

Table 1 — Three types of combined lines
Code Type Content
T T type combined line link without roller type combined line, see Figure 1
M M type combined line link with roller type combined line, see Figure 2
C C type combined line cow hitch type combined line, see Figure 3
4.2 Structure
The T type combined line is shown in Figure 1.
Dimensions in millimetres
Key
1 mooring rope
2 link without roller
3 tail
L length of mooring rope
L length of tail
NOTE L and L can be selected according to users’ demands.
1 2
Figure 1 — T type combined line
The M type combined line is shown in Figure 2.
Dimensions in millimetres
Key
1 mooring rope
2 link with roller
3 tail
L length of mooring rope
L length of tail
NOTE L and L can be selected according to users’ demands.
1 2
Figure 2 — M type combined line
The C type combined line is shown in Figure 3.

Dimensions in millimetres
Key
1 mooring rope
2 haulage rope
3 tail
L length of mooring rope
L length of tail
NOTE 1 L and L can be selected according to users’ demands.
1 2
NOTE 2 The haulage rope with Φ10 mm to Φ16 mm can be selected for separating the mooring rope and tail.
Figure 3 — C type combined line
4.3 Codes
The codes of the main components of combined lines are shown in Table 2. The applicable standards listed
in Table 2 shall apply.
Table 2 — Codes of main components
Items Material components Applicable standard Code
steel wire rope ISO 2408 WR
high modulus polyethylene (HMPE) rope ISO 10325 HP
mooring rope
LCP fibre rope — LCP
aramid fibre rope — AR
a
connection device X20Cr13 or equal strength material ISO 16143-1 GS
polyamide rope ISO 1140 SR1
tail polyester rope ISO 1141 SR2
fibre ropes of polyester or polyolefin dual fibres ISO 10556 SR3
a
X20Cr13 is a material grade specified in ISO 16143-1.
5 Design requirements
5.1 General
The combined lines shall be designed as follows:
a) The line design break force (LDBF) of the mooring rope shall be 100 % to 105 % of the ship design
minimum breaking load (MBL).
b) Steel wire ropes shall have a working load limit (WLL) of 55 % of the ship design MBL, and fibre ropes
shall have a WLL of 50 % of the ship design MBL.

c) The ultimate load of the connection devices shall be three times the safe working load. The test tension
of the connection devices shall not be less than twice its own safe working load.
d) The TDBF of tails shall be 125 % to 130 % of the ship design MBL.
e) The surface quality of steel wire ropes and their strands shall comply with the requirements of ISO 2408.
f) The cyclic loading dependent on line design shall be considered. Predictive cyclic loading models for
steel wire and synthetic fibre line are not able to account for the complex and varied conditions most
mooring lines experience in service.
g) The break force of mooring line materials shall be specified at varied temperatures (−20 °C, 0 °C, 20 °C,
40 °C, 60 °C, 80 °C).
h) Immediate strain is measured at 10 %, 20 %, 30 %, 40 % and 50 % of the design break force.
i) It shall be ensured that appropriate D/d ratios are specified during ship design, so as to manage the line
degradation caused by line bending through the line management plan.
NOTE D/d ratio refers to the diameter of the bend divided by the diameter of the mooring line.
5.2 Specifications
5.2.1 Steel wire rope used as mooring line
5.2.1.1 The product design, test and inspection of steel wire ropes shall be in accordance with ISO 2408.
5.2.1.2 The breaking force of steel wire ropes shall meet the requirements of ISO 2408:2017, 4.5.
5.2.1.3 When steel wire ropes are used as mooring ropes, independent wire rope core (IWRC) of class
6 × 36 and class 6 × 41 parallel twist or conventional right reciprocal twisting and left alternate twist steel
ropes shall be selected.
5.2.1.4 The minimum tensile strength of steel wire ropes shall not be less than 1 770 N/mm . Specifications
of steel wire ropes are listed in Table A.1.
5.2.2 Synthetic fibre rope as mooring line
5.2.2.1 The product design, test and inspect of synthetic fibre ropes shall be in accordance with ISO 9554.
5.2.2.2 The linear density of synthetic fibre ropes shall be calculated in accordance with ISO 2307:2019, 11.2.
5.2.2.3 The diameter of synthetic fibre ropes shall be measured and calculated in accordance with
ISO 2307:2019, 11.3.
5.2.2.4 The breaking strength of synthetic fibre ropes shall be measured in accordance with ISO 2307:2019,
Clause 9, and shall be reported as the spliced breaking strength value.
5.2.2.5 When HMPE fibre rope is used as a mooring rope, it may be either 8-strand (L type), 12-strand (T
type), or jacketed (C type) as specified in ISO 10325. Preferred specifications of HMPE fibre ropes are listed
in Table A.2.
5.2.2.6 When LCP fibre rope is used as a m
...