ISO/TS 25128:2026

Technical
Specification
ISO/TS 25128
First edition
Small craft — Propulsion system
2026-09
energy consumption — Test method
Petits navires — Consommation d'énergie du système de
propulsion — Méthode d'essai
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General test conditions . 2
4.1 Payload .2
4.1.1 General .2
4.1.2 Performance test mass .2
4.1.3 Maximum load .3
4.2 Fuel type .3
4.3 Engine(s)/motor(s) and propeller(s) .3
4.4 Measurement and calculation method for craft energy consumption .4
4.4.1 General .4
4.4.2 Measurement of energy consumption at the motor or engine .4
4.4.3 Measurement and establishment of the energy conversion or efficiency factor .4
4.5 System configuration .4
4.6 Energy consumption of non-essential systems .5
5 Test conditions . 5
5.1 State of propulsion system .5
5.2 Sea state .5
5.3 Wind conditions .5
5.4 Air temperature .5
5.5 Water temperature .5
5.6 Salinity .6
6 Test procedures . 6
6.1 General .6
6.1.1 Course .6
6.1.2 Water depth .6
6.1.3 Stabilization .6
6.2 Test Stage 1 .6
6.3 Test Stage 2 .7
7 Documentation of results . 7
8 Presentation of results . 8
8.1 Energy consumption .8
8.2 Range . .10
Bibliography .11

iii
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
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This document was prepared by Technical Committee ISO/TC 188, Small craft.
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.

iv
Introduction
This document establishes a comprehensive test framework for assessing energy use of propelled small
craft when navigating. The assessment encompasses both added energy, originating from the fuel or power
source propelling craft, and non-added energy, comprising forces from wind, currents and waves influencing
the craft’s movement.
The methodologies outlined not only enable consumers to evaluate energy use but also provide a tool for
understanding the environmental impact and operational costs associated with various craft types.
The specific use of this document is twofold. It enables consumers to have a common and comparable
baseline to evaluate trade-offs between craft models and/or propulsion systems, while enabling consumers
to acquire knowledge about the most energy efficient operational conditions of a specific craft model and/or
propulsion system.
In this document, energy use is a way of expressing energy in a common unit for use in comparisons and
trade-offs between different craft models, propulsion systems and other modes of transport. The energy
assessment to be determined includes some or all values reflected in the concept of total energy use.
This document does not include recommendations regarding the selection of energy sources. Furthermore,
the energy assessment detailed herein excludes considerations related to the energy expended in the
production of craft.
v
Technical Specification ISO/TS 25128:2026(en)
Small craft — Propulsion system energy consumption — Test
method
1 Scope
This document specifies requirements for the measurement, documentation and presentation of mechanical
propulsion energy consumption for small craft underway, irrespective of the propulsion system, type of
energy or hull characteristics.
This document does not apply to wind, wind-assisted hybrid and wave propulsion systems.
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 8665 (all parts), Small craft — Power measurements and declarations
ISO 8666:2020, Small craft — Principal data
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
propulsion system
system converting an energy source into kinetic energy to propel a craft (3.5)
3.2
energy system
system converting energy stored in a device to kinetic energy
3.3
maximum load
m
ML
load which the craft (3.5) is designed to carry in addition to the light craft condition
Note 1 to entry: The light craft condition is described in ISO 8666:2020, 7.5.
3.4
combustion engine
engine
energy converter, other than a gas turbine, designed to transform chemical energy (input) into mechanical
energy (output) with an internal combustion process

3.5
craft
small craft
recreational boat, and other watercraft using similar equipment, of up to 24 m length of hull (L )
H
[SOURCE: ISO 8666:2020, 3.15]
3.6
sailing craft
craft (3.5) for which the primary means of propulsion is by wind power, having a reference sail area (A )
S
2/3
(3.8) ≥ 0,07 (m )
LDC
Note 1 to entry: A is expressed in metres squared.
S
Note 2 to entry: m is the mass of the craft in the maximum load (3.3) condition, expressed in kilograms.
LDC
3.7
non-sailing craft
craft (3.5) for which the primary means of propulsion is other than by wind power, having a reference sail
2/3
area (A ) (3.8) < 0,07(m )
S LDC
Note 1 to entry: A is expressed in metres squared.
S
Note 2 to entry: m is the mass of the craft in the maximum load (3.3) condition, expressed in kilograms.
LDC
3.8
reference sail area
A
S
actual profile area of sails set abaft a mast, plus the maximum profile areas of all masts, plus reference
triangle area(s) forward of each mast
4 General test conditions
4.1 Payload
4.1.1 General
Sailing craft shall be loaded and equipped in accordance with 4.1.2.
Non-sailing craft shall be loaded and equipped in accordance with 4.1.2 and 4.1.3.
4.1.2 Performance test mass
The performance test mass (m ) of a craft shall include all permanently attached standard items of
P
equipment. Further, the craft shall be fitted with all items of loose equipment needed for the safe operation
of the craft, for example:
— warps;
— anchors/chain/ropes;
— engine(s);
— batteries.
In addition, the masses of the following shall be included:
— number of persons needed for the safe operation of the craft;
— fuel at least at 25 %, but no more than 50 % of the tank capacity of permanent
...