ISO 8728:2014

INTERNATIONAL ISO
STANDARD 8728
Third edition
2014-08-01
Ships and marine technology —
Marine gyro-compasses
Navires et technologie maritime — Compas gyroscopiques à usage
marin
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Construction . 2
5 Performance requirements . 4
5.1 Accuracy in latitudes up to 60° . 4
5.2 Interface . 5
6 Type tests . 5
6.1 General . 5
6.2 Settling time test . 5
6.3 Settle point error test . 5
6.4 Settle point heading repeatability test . 5
6.5 Settling time on a Scorsby table . 6
6.6 Scorsby test . 6
6.7 Intercardinal motion test . 7
6.8 Repeater accuracy test . 7
6.9 Speed correction test . 7
6.10 General requirement test . 8
6.11 Interface test .10
7 Marking .10
8 Information .10
Annex A (normative) Advice to ship surveyors for installation of gyro-compasses and repeater
compasses on board ships .11
Annex B (informative) Equivalent requirements in ISO 8728 and IMO Resolution .12
Bibliography .14
Foreword
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The committee responsible for this document is ISO/TC 8, Ships and marine technology, Subcommittee
SC 6, Navigation and ship operations.
This third edition cancels and replaces the second edition (ISO 8728:1997), which has been technically
revised.
iv © ISO 2014 – All rights reserved

INTERNATIONAL STANDARD ISO 8728:2014(E)
Ships and marine technology — Marine gyro-compasses
1 Scope
This International Standard specifies the construction, performance, and type testing for gyro-compasses
required by Regulation 12 of Chapter V of SOLAS 1974 (as amended).
NOTE All requirements that are extracted from the recommendations of IMO Resolutions [Resolution
A.424(XI) on performance standards for gyro-compasses] are printed in italics.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 25862, Ships and marine technology — Marine magnetic compasses, binnacles and azimuth reading
devices
IEC 60945, Maritime navigation and radiocommunication equipment and systems — General requirements
— Methods of testing and required test results
IEC 61162-1, Marine navigation and radiocommunication equipment and systems — Digital interfaces -
Part 1: Single talker and multiple listeners
IEC 61162-2, Maritime navigation and radiocommunication equipment and systems — Digital interfaces —
Part 2: Single talker and multiple listeners, high-speed transmission
IEC 61924-2, Maritime navigation and radiocommunication equipment and systems — Integrated Navigation
Systems (INS) — Part 2: Modular structure for INS — Operational and performance requirements, methods
of testing and required test results
IMO Resolution MSC.252(83), Performance standards for alert communications with an Integrated
Navigation System
IMO Resolution MSC.302(87), Performance standards for bridge alert management
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
gyro-compass
complete equipment including all essential elements of the complete design, including both the gyro-
compass as heading sensor and the associated heading transmission system
3.2
true heading
horizontal angle between the vertical plane passing through the true meridian and the vertical plane passing
through the ship’s fore-and-aft datum line; it is measured from true north (000°) clockwise through 360°
Note 1 to entry: When the gyro-compass equipment is not installed on board ship, this “true heading” is regarded
as the true heading of the lubber line. Where a gyro-compass has the facility of introducing a correction by moving
the lubber line, the correction is set for the local latitude.
3.3
settled
stable situation when any three readings taken at intervals of 30 min are within a band of 0,7°, with the
compass level and stationary
Note 1 to entry: The settling time is the elapsed time between the time of switch-on at the initial heading error
and the third recording of the settle.
3.4
settle point heading
mean value of ten readings taken at 20 min intervals after the compass has settled as defined in 3.3
3.5
settle point error
difference between the settle point heading as defined in 3.4 and the true heading
3.6
error
difference between the observed value and the settle point heading as defined in 3.4
3.7
bearing repeater compass
device that reproduces the master compass card at a remote location
3.8
compass card
graduated dial of the compass which indicates the measured direction of the meridian
3.9
latitude error
error to which some gyro-compasses are subject, the magnitude and sign of which depend upon the
local latitude
Note 1 to entry: Means are provided for correcting this error.
3.10
speed error
error to which gyro-compasses are subject, the magnitude and sign of which depend upon the speed,
course, and latitude of the ship
Note 1 to entry: Means are provided for correcting this error.
3.11
lubber line
index line situated on the body of a compass against which the compass heading is read
3.12
master compass
main compass unit which supplies the heading information to the repeaters and other navigational aids
3.13
scorsby table
test machine which independently oscillates a platform about three axes; it is used to simulate the
motion of a ship
4 Construction
Gyro-compass units shall conform to the following requirements.
2 © ISO 2014 – All rights reserved

4.1 The equipment shall be capable of continuous operation under conditions of vibration, humidity,
change of temperature and variations of the power supply as specified in 6.10.1 to 6.10.5.
4.2 For those ships which are required to carry bearing repeater compasses, the construction of these
shall be as follows.
a) The bearing repeater compass shall be designed to be fitted with an azimuth reading device.
b) A gimbal mechanism shall be provided to enable the bearing repeater compass card to be held
horizontally against the ship’s motion.
c) Any bearing repeater compass intended for use on an open deck shall be waterproof.
4.3 The compass card shall be graduated at equal intervals of 1° or fraction thereof.
The graduation error shall be less than ±0,2°.
A numerical indication shall be provided at least at every 10°, starting from 000° clockwise through 360°.
4.4 Fully adequate illumination shall be provided to enable the reading of all compass cards at all times.
Facilities for dimming shall be provided.
4.5 Both master compass and repeater compasses shall be provided with a lubber line to indicate the
ship’s heading.
4.5.1 The base or some other fixed extremity of the compass shall be marked or identified in such a way
as to facilitate the installation of the compass in a ship, so that the lubber line lies in a vertical fore-and-aft
plane of the ship. Where a gyro-compass has the facility of introducing a correction by moving the lubber
line, the correction during installation shall be set to zero.
If such marks or identifications are not in the same vertical planes as the uncorrected lubber line, then
the horizontal angular relationship between them shall be clearly indicated.
4.6 Means shall be provided for correcting the errors induced by speed and latitude. Graphical or tabular
means of correction can be used.
4.7 Steps shall be taken to eliminate as far as is practical, the causes of and to suppress electromagnetic
interference between the gyro-compass and other equipment on board.
4.8 Mechanical noise from all units shall be so limited as to ensure the hearing of sounds on which the
safety of the ship may depend.
4.9 The equipment shall be so constructed that it is readily accessible for maintenance purposes.
1)
4.10 An automatic alert shall be provided to indicate malfunctions of the system or a power failure in
the gyro-compass. The alert shall conform to the presentation and handling requirements of Bridge Alert
Management [IMO Res. MSC.302(87)]. A suitable interface shall be provided for alert communications
with an Integrated Navigation System [IMO Res. MSC.252(83) and IEC 61924-2].
The following sentences shall be provided for the alert communications interface:
Sentences transmitted by the gyro-compass:
— ALR, HBT: See IEC 61162-1;
1) The term “alarm” was replaced by “alert” in accordance with IMO Resolution MSC.252(83) and IMO Resolution
MSC.302(87).
— ALC, ALF, ARC: See IEC 61924-2.
Sentences received by the gyro-compass:
— ACK, HBT: See IEC 61162-1;
— ACN: See IEC 61924-2.
4.11 Means shall be incorporated for the protection of the equipment from excessive currents and voltages,
transients and accidental reversal of power supply polarity.
4.12 If provision is made for operating the equipment from more than one source of electrical energy,
arrangements for rapidly changing from one source of supply to the other shall be incorporated.
4.13 The gyro-compass shall be designed to enable heading information to be provided to other
navigational aids.
5 Performance requirements
5.1 Accuracy in latitudes up to 60°
5.1.1 Settling time
When switched on in accordance with the manufacturer’s instructions, the compass shall settle within 6 h.
5.1.2 Settle point error
5.1.2.1 The settle point error as defined in 3.5 at any heading shall not exceed ± 0,75° × secant latitude, and
the RMS value of the differences between individual heading indications and the mean value shall be less
than 0,25° × secant latitude.
5.1.2.2 The repeatability of settle point error from one run-up to another shall be within 0,25° × secant
latitude.
5.1.3 Settling time under operational conditions
When switched on in accordance with the manufacturer’s instructions, the compass shall settle within 6
h when rolling and pitching with simple harmonic motion of any period between 6 s and 15 s, a maximum
angle of 5°, and a maximum horizontal acceleration of 0,22 m/s .
5.1.4 Settle point error under general conditions
The repeatability of the settle point error of the master compass shall be within ± 1° × secant latitude under
the general conditions and including variations in magnetic fields likely to be experienced in the ship in
which it is installed.
5.1.5 Residual error in correction
The residual steady-state error, after correction for speed and course influences at a speed of 20 kn, shall not
exceed ±0,25° × secant latitude.
5.1.6 Effect of alteration of speed
The error due to a rapid alteration of speed of 20 kn shall not exceed ±2°.
4 © ISO 2014 – All rights reserved

5.1.7 Effect of alteration of course
The error due to a rapid alteration of course of 180° at a speed of 20 kn shall not exceed ±3°.
5.1.8 Accuracy on a Scorsby table
The transient and steady-state errors due to rolling, pitching, and yawing, with simple harmonic motions of
any period between 6 s and 15 s, maximum angles of 20°, 10°, and 5° respectively, and a maximum horizontal
acceleration not exceeding 1 m/s , shall not exceed ±1° × secant latitude.
5.1.9 Synchronization between the master compass and repeaters
Once the repeaters have been synchronized with the master, the maximum divergence in reading between
the master compass and repeaters under all op
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