ISO 21321:2026

Ships and marine technology — Human-occupied submersibles — Manoeuvring tests

This document specifies the general requirements, test items and methods for conducting manoeuvring tests on human-occupied submersibles. It is applicable to manoeuvring tests for all human-occupied submersibles operating in the sea and inland waterway areas. It can also be used as a reference for manoeuvring tests on other types of submersibles operating in pools, lakes and seas.

Navires et technologie maritime — Submersibles habités — Essais de manœuvre

General Information

• Status: Published
• Publication Date: 28-Apr-2026
• ICS: 47.080 - Small craft
• Technical Committee: ISO/TC 8/SC 13 - Marine technology
• Drafting Committee: ISO/TC 8/SC 13 - Marine technology
• Current Stage: 6060 - International Standard published
• Start Date: 29-Apr-2026
• Due Date: 27-Jul-2026
• Completion Date: 29-Apr-2026

Overview

ISO 21321: Ships and Marine Technology – Human-Occupied Submersibles – Manoeuvring Tests establishes internationally recognized requirements and test methods for evaluating the manoeuvring performance of manned submersibles. Developed under ISO/TC 8/SC 13, this standard is applicable to all human-occupied submersibles operating in pools, lakes, and sea environments. The document’s harmonized testing protocols help ensure safety, reliability, and consistency in submersible operations and development.

Adhering to ISO 21321 brings confidence to manufacturers, operators, and regulatory authorities by defining general requirements, essential test items, and consistent procedures for conducting manoeuvring tests. Additionally, these standardized methods serve as a reference for other submersible types, supporting a broad range of applications in research, industrial, and exploration settings.

Key Topics

ISO 21321 covers the following core aspects related to manoeuvring testing for manned submersibles:

• General Requirements: Emphasizes the use of suitable support vessels, validated test instruments, appropriate test conditions, and robust emergency procedures for all manoeuvring tests.
• Test Items and Methods: Outlines a series of test types essential for comprehensive assessment, including:
  • Physical buoyancy tests
  • Powered and unpowered submerging and surfacing tests
  • Auto-depth, auto-heading, and auto-altitude (height) control tests
  • Triple-direction speed and stopping distance measurements
  • Turning and hovering performance evaluations
• Test Equipment: Specifies recommended instruments such as doppler velocity logs, depth gauges, altimeters, motion sensors, and CTD sensors, as well as requirements for proper installation and calibration.
• Safety and Operational Guidelines: Stresses requirements for pre-dive checks, environmental monitoring, and detailed trial documentation for traceability and emergency response readiness.

Applications

Adopting ISO 21321 is vital for a wide range of real-world applications, including:

• Submersible Manufacturing and Commissioning: Ensures that new human-occupied submersibles meet defined performance and safety benchmarks before deployment.
• Operator Training and Certification: Provides a framework for consistent training standards and performance verification for submersible crews.
• Research and Scientific Missions: Supports research teams by facilitating reliable and safe manoeuvrability, enabling efficient data collection and underwater navigation.
• Commercial Operations: Essential for underwater tourism, inspection, and resource exploration companies to demonstrate compliance with international safety and manoeuvring test requirements.
• Regulatory Compliance and Audits: Serves as a reference for government authorities and certifying agencies to assess submersible performance and operational readiness.

Related Standards

ISO 21321 complements and references other standards in the marine and submersible technology field, including:

• ISO 5411 – Ships and Marine Technology – Submersibles – Vocabulary: Provides standardized terminology critical for consistent interpretation and application of ISO 21321 across international boundaries.
• Other Marine Technology and Safety Standards: ISO 21321 aligns with broader ISO frameworks for vessels and marine operations, supporting safety management systems and technical auditing in the marine industry.

By implementing ISO 21321, organizations contribute to a safer, more reliable, and internationally standardized approach to the design, testing, and operation of manned submersibles, strengthening confidence for users and stakeholders in the marine technology sector.

Standards Content (Sample)

International
Standard
ISO 21321
First edition
Ships and marine technology —
2026-04
Human-occupied submersibles —
Manoeuvring tests
Navires et technologie maritime — Submersibles habités —
Essais de manœuvre
Reference number
© ISO 2026
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General requirements and recommendations. 2
4.1 Support vessel .2
4.2 Test instruments .2
4.3 Test conditions .3
4.4 Emergency operating procedures .3
5 Test types . 3
6 Test methods . 4
6.1 Submersible designed physical buoyancy test .4
6.1.1 Test purpose .4
6.1.2 Test procedure.4
6.1.3 Measuring parameters .4
6.1.4 Test result .4
6.2 Powered submerging test .4
6.2.1 Test purpose .4
6.2.2 Test procedure.4
6.2.3 Measuring parameters .5
6.2.4 Test result .5
6.3 Unpowered surfacing with releasable ballast response test .5
6.3.1 Test purpose .5
6.3.2 Test procedure.5
6.3.3 Measuring parameters .5
6.3.4 Test result .6
6.4 Powered surfacing test .6
6.4.1 Test purpose .6
6.4.2 Test procedure.6
6.4.3 Measuring parameters .6
6.4.4 Test result .6
6.5 Auto-depth test .7
6.5.1 Test purpose .7
6.5.2 Test procedure.7
6.5.3 Measuring parameters .7
6.5.4 Test result .7
6.6 Auto-heading test .7
6.6.1 Test purpose .7
6.6.2 Test procedure.7
6.6.3 Measuring parameters . .8
6.6.4 Test result .8
6.7 Triple-direction speed test .8
6.7.1 Test purpose .8
6.7.2 Test procedure.8
6.7.3 Record requirement .8
6.7.4 Measuring parameters . .8
6.7.5 Test result .9
6.8 Stopping distance test .9
6.8.1 Test purpose .9
6.8.2 Test procedure.9
6.8.3 Measuring parameters .9
6.8.4 Test result .9

iii
6.9 Turning test .9
6.9.1 Test purpose .9
6.9.2 Test procedure.10
6.9.3 Measuring parameters .10
6.9.4 Test result .10
6.10 Auto-altitude test .10
6.10.1 Test purpose .10
6.10.2 Test procedure.10
6.10.3 Measuring parameters .10
6.10.4 Test result .11
6.11 Hovering test .11
6.11.1 Test purpose .11
6.11.2 Test procedure.11
6.11.3 Measuring parameters .11
6.11.4 Test result .11
Annex A (informative) Record tables .12
Bibliography .24

iv
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
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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)
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This document was prepared by Technical Committee ISO/TC 8, Ships and marine technology, Subcommittee
SC 13, Marine technology.
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.

v
Introduction
1)
As global marine technology continues to develop, human-occupied submersibles are being utilized in an
increasing number of fields. A standardized manoeuvring test for human-occupied submersibles may be
employed to provide a common approach to the analysis and assessment of the manoeuvrability performance
of newly built submersibles. The output of such a common approach can provide useful information for the
design, development and selection of navigation, power management and other ancillary systems used in
the subsequent completion of the submersible’s manufacture.
To meet the operating safety requirements, it is essential that the manoeuvring test is conducted within
the designed safe operating envelope of the submersible including environmental, depth and endurance
parameters. The measurement of manoeuvring performance is expected to be accurate and verifiable
against an appropriately considered set of performance expectations. However, at the time of publication
of this document, there is no International Standard that covers this element of submersible design and
development in the industry. Therefore, the aim of this document is to provide standardized requirements
for the submersible manufacturing and operating community.
1) This document uses the inclusive term "human-occupied submersible" in place of the term "manned submersible".

vi
International Standard ISO 21321:2026(en)
Ships and marine technology — Human-occupied
submersibles — Manoeuvring tests
1 Scope
This document specifies the general requirements, test items and methods for conducting manoeuvring
tests on human-occupied submersibles.
It is applicable to manoeuvring tests for all human-occupied submersibles operating in the sea and inland
waterway areas.
It can also be used as a reference for manoeuvring tests on other types of submersibles operating in pools,
lakes and seas.
2 Normative references
There are no normative references in this document.
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
human-occupied submersible
submersible that encloses one or more persons within its pressure hull, fitted with one or more available
surface accesses, or underwater pressurized or non-pressurized accesses
[SOURCE: ISO 5411:2024, 3.1.2, modified — the term has been modified from "manned submersible" to the
inclusive term "human-occupied submersible".]
3.2
unpowered surfacing
free rising movement of a human-occupied submersible (3.1) which occurs without the use of propulsion or
operation of the submersible's ballast system
3.3
unpowered submerging
free sinking movement of a human-occupied submersible (3.1) which occurs without the use of propulsion or
operation of the submersible's ballast system
3.4
auto-depth keeping
computer-controlled mode to maintain the designated depth relative to the surface
[SOURCE: ISO 5411:2024, 3.9.6]

3.5
auto-heading control
computer-controlled mode to maintain the designated heading relative to the seabed
[SOURCE: ISO 5411:2024, 3.9.4]
3.6
auto-height keeping
computer-controlled mode to maintain the designated height above the seabed
[SOURCE: ISO 5411:2024, 3.9.7]
3.7
stopping distance
distance from slow down to stop with the use of propulsion, when a human-occupied submersible (3.1) travels
at an initial speed
3.8
design maximum safe operating depth
maximum water depth at which the submersible is permitted to operate repeatedly and normally throughout
its entire design life
4 General requirements and recommendations
4.1 Support vessel
For all submersible trial activities undertaken in open water such as the sea or an inland lake, a trial support
surface vessel should be available to ensure the safe conduct of the trial programmes and meet any relevant
requirements. If required, the support vessel should be capable of safely launching and recovering the
submersible in the safe operating envelope of the submersible system. It can be necessary for the support
vessel to be capable of dynamic positioning or mooring, thereby enabling the safe launch and recovery to be
conducted in the environmental conditions in which the trials will take place. The vessel should be capable
of dealing with any foreseeable emergency likely to be encountered during the trial programmes. The vessel
should also have a robust communication capability such that the submersible’s crew can communicate with
the support vessel at all times during the trials and testing activities.
4.2 Test instruments
Test instruments include but are not limited to:
a) doppler velocity log;
b) depth gauge;
c) altimeter;
d) motion sensor;
e) conductivity, temperature and depth (CTD) sensor;
f) positioning system.
NOTE Test instruments can be subject to approval by national authorities for use in the testing process.
Test instruments should be valid for use in the testing regime and as required by the testing protocol.
Test instruments should be installed in a suitable location to achieve the objective of the test process and not
adversely affected by movement, moisture, vibration or external environmental conditions during the test.

4.3 Test conditions
The test shall be conducted in a designated sea or inland waterway area where the water depth should be
less than the design maximum safe operating depth of the human-occupied submersible. The specified test
depth should not be affected by surface waves and appropriate safety precautions shall be implemented.
This should include a suitably considered plan for recovery of a disabled submersible from the seabed or
bottom of the inland waterway and establishing a safe depth which the submersible should not cross without
approval.
The temperature, salinity, dept
...