ISO 21321:2026

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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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
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This document was prepared by Technical Committee ISO/TC 8, Ships and marine technology, Subcommittee
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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
...