ISO 21711:2019

Marine structures - Mobile offshore units - Chain wheels

This document specifies the requirements for the profiles, dimensions, tolerances, materials and inspection of chain wheels for chains on mobile offshore units. Chain wheels meeting the requirements of this document can be used with offshore mooring chains conforming to ISO 20438.

Structures maritimes — Unités mobiles au large — Pignons à chaîne

General Information

• Status: Published
• Publication Date: 23-Apr-2019
• ICS: 47.020.50 - Deck equipment and installations
• Technical Committee: ISO/TC 8/SC 4 - Outfitting and deck machinery
• Drafting Committee: ISO/TC 8/SC 4/WG 2 - Deck machinery
• Parallel Committee: ISO/TC 4 - Rolling bearings
• Current Stage: 9093 - International Standard confirmed
• Start Date: 03-Sep-2024
• Completion Date: 13-Dec-2025

Overview

ISO 21711:2019 specifies requirements for chain wheels used on mobile offshore units (MOUs). The standard covers tooth profiles, nominal dimensions, dimensional and geometric tolerances, material selection and inspection requirements for chain wheels intended to work with offshore mooring chains conforming to ISO 20438. Chain wheels are classified by tooth count (Type A = 5-tooth, Type B = 6-tooth, Type C = 7-tooth) and designated using the format e.g. Chain wheel ISO 21711:2019 A56.

Key topics and technical requirements

• Profiles & dimensions: Nominal tooth profiles and dimensional tables are defined for the 5-, 6- and 7-tooth chain wheels to ensure correct engagement with stud-link mooring chains.
• Tolerances:
  • Linear dimensional tolerances for castings: conform to ISO 8062-3, DCTG 11.
  • Geometric tolerances for castings: conform to ISO 8062-3, GCTG 7.
• Materials: Selection of base materials is linked to mooring chain grades (R3, R3S, R4, R4S, R5).
• Tooth surface hardness: Tooth hardness at the meshing zone should be compatible with the chain hardness and may be up to 10% higher depending on service conditions. Hardness can be achieved by heat treatment or embedding wear‑resistant materials.
• Inspection & testing:
  • Dimensional/geometric inspection per ISO 8062-3 requirements.
  • Visual surface quality inspection referenced to ISO 11971 (under preparation at publication).
  • Tooth hardness testing per ISO 6506-1 (Brinell) or ISO 16859-1 (Leeb).
  • Material traceability: product inspection certificate from the classification society required for chain wheel blanks.

Applications and users

ISO 21711:2019 is intended for use where reliable chain‑wheel / mooring‑chain interaction is critical:

• Offshore vessel and mobile offshore unit designers and shipyards specifying deck machinery.
• Manufacturers of chain wheels, capstans, windlasses and mooring equipment.
• Classification societies, inspection bodies and procurement teams for quality control and certification.
• Maintenance and diving/anchor-handling teams ensuring safe mooring operations.

Practical benefits include improved interchangeability, predictable load transmission (pitch diameter defined for torque calculations), wear control through hardness specification, and consistent inspection criteria.

Related standards

• ISO 20438 - Offshore mooring chains (compatibility target)
• ISO 8062-3 - Dimensional and geometrical tolerances for castings
• ISO 6506-1 - Brinell hardness test (metallic materials)
• ISO 16859-1 - Leeb hardness test (metallic materials)
• ISO 11971 - Visual examination of steel and iron castings (under preparation)

Keywords: ISO 21711:2019, chain wheels, mobile offshore units, offshore mooring chains, chain wheel dimensions, tooth surface hardness, chain wheel inspection, marine structures.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21711
First edition
2019-04
Marine structures — Mobile offshore
units — Chain wheels
Structures maritimes — Unités mobiles au large — Pignons à chaîne
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification . 2
4.1 Types of the chain wheels . 2
4.2 Designation . 7
5 Requirements . 7
5.1 Geometric tolerance and dimensional tolerance . 7
5.2 Materials . 8
6 Inspection . 8
6.1 Dimensional and geometric inspection . 8
6.2 Visual inspection for surface quality . 8
6.3 Inspection of tooth surface hardness . 8
6.4 Material inspection. 8
Bibliography . 9
Foreword
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This document was prepared by Technical Committee ISO/TC 8, Ships and marine technology,
Subcommittee SC 4, Outfitting and deck machinery.
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iv © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 21711:2019(E)
Marine structures — Mobile offshore units — Chain wheels
1 Scope
This document specifies the requirements for the profiles, dimensions, tolerances, materials and
inspection of chain wheels for chains on mobile offshore units.
Chain wheels meeting the requirements of this document can be used with offshore mooring chains
conforming to ISO 20438.
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 3828, Shipbuilding and marine structures — Deck machinery — Vocabulary and symbols
ISO 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method
ISO 8062-3, Geometrical product specifications (GPS) — Dimensional and geometrical tolerances for
moulded parts — Part 3: General dimensional and geometrical tolerances and machining allowances for
castings
1)
ISO 11971:— , Steel and iron castings — Visual examination of surface quality
ISO 16859-1, Metallic materials — Leeb hardness test — Part 1: Test method
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3828 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
pitch diameter
D
p
circumscribed circle diameter of the regular polygon formed by the centerline of the stud-link anchor
chain where the anchor chain is engaged with the chain wheel
Note 1 to entry: Pitch diameter is used to calculate the maximum torque of the anchor chain during operation.
3.2
speed calculation diameter
D
v
diameter of the moving line of the stud-link anchor chain when anchoring with power
1) Under preparation. Stage at the time of publication: ISO/DIS 11971:2018.
4 Classification
4.1 Types of the chain wheels
a) Type A — 5-tooth chain wheel, see Figure 1 for the tooth profile structure. The nominal dimensions
are given in Table 1.
It is not recommended to select values in the shaded area.
Figure 1 — Tooth profile structure of type A chain wheel
2 © ISO 2019 – All rights reserved

b) Type B — 6-tooth chain wheel, see Figure 2 for the tooth profile structure. The nominal dimensions
are given in Table 1.
It is not recommended to select values in the shaded area.
Figure 2 — Tooth profile structure of type B chain wheel
c) Type C — 7-tooth chain wheel, see Figure 3 for the tooth profile structure. The nominal dimensions
are given in Table 1.
It is not recommended to select values in the shaded
...