Annex 2 - Recommendation on Performance Standards for Marine Transmitting Magnetic Heading Devices (TMHDs)
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Statutory Documents - IMO Publications and Documents - Resolutions - Maritime Safety Committee - Resolution MSC.86(70) - Adoption of New and Amended Performance Standards for Navigational Equipment - (Adopted on 8 December 1998) - Annex 2 - Recommendation on Performance Standards for Marine Transmitting Magnetic Heading Devices (TMHDs)

Annex 2 - Recommendation on Performance Standards for Marine Transmitting Magnetic Heading Devices (TMHDs)

 1 SCOPE

1.1 A TMHD is an electronic device which uses the geomagnetic field to obtain and transmit information about the ship’s heading.

1.2 In addition to the general requirements contained in resolution A.694(17)footnote all marine TMHD equipment should comply with the following minimum requirements.

2 APPLICATION

2.1 A TMHD complying with the requirements contained in this recommendation, can be used to meet the carriage requirements for a suitable device providing heading information contained in Chapter V of the SOLAS Convention.

2.2 In addition such THMD can meet the dynamic requirements contained in the HSC Code chapter 13 for the carriage of a suitable device providing heading information.

3 COMPOSITION

3.1 Transmitting magnetic heading devices (TMHDs) may comprise of:

  • .1 a standard magnetic compass equipped with a magnetic sensor and electronics for generating a suitable output signal for other devices. The compass used should be the standard magnetic compass provided under SOLAS chapter V; or

  • .2 an electromagnetic compass consisting of the sensor part and electronics for generating a suitable output signal for other devices; or

  • .3 any type as defined under .1 and .2 additionally equipped with a rate gyro to improve dynamic performance.

4 CONSTRUCTION

4.1 Fore-and-aft mark

4.1.1 A fore-and-aft mark should be inscribed on the magnetic sensor housing, which should be installed in parallel to the ship’s fore-and-aft line.

4.1.2 The accuracy of the fore-and-aft mark should be within ± 0.5° to the fore-and-aft direction of the housing.

4.1.3 If a rate gyro is installed it should be marked in the same way and additionally be marked with top or bottom.

4.2 Fitting

4.2.1 Provision should be made, in the mounting arrangements of the magnetic sensor, for correction of any misalignment, up to ± 5°, with respect to the fore-and-aft line.

4.2.2 The fitting of the sensor arrangement to the compass in paragraph 3.1 above should still enable the compass to comply with resolution A.382(X) with particular reference to accuracy, gimbling and use of the azimuth reading device.

4.3 Compensation of deviation and heeling error

  • Provision should be made to correct the deviation and heeling error and it should be possible to correct the following values:footnote

  • .1 vertical component of the ship's magnetic field (producing the heeling error): up to ±75 μT;

  • .2 coefficient A: up to ±3°;

  • .3 coefficient B: up to ±(720/H)°;

  • .4 coefficient C: up to ±(720/H)°;

  • .5 coefficient D: up to ±7°; and

  • .6 coefficient E: up to ± 3°,

where H is the horizontal component of the geomagnetic flux density in microteslas (μT).

4.3.1 Indication of compensation

  • The values used for electronic compensation should be indicated by adequate means and should be stored such that values are automatically recovered on switch-on.

4.3.2 Protection of compensation

  • The compensating devices should be protected against inadvertent operation.

4.4 Heading output

  • All displays and outputs of heading should indicate true heading. An indication of any deviation and variation applied to compensate the heading should be capable of being displayed or included in the output.

4.5 Interfaces

  • The TMHD should be so designed to transmit heading information to other equipment. At least one output should be in accordance with the relevant international marine interface standard.footnote

5 PERFORMANCE

  • The following performance standards are required to be achieved under the conditions of a value of 18 μT of the horizontal component of the geomagnetic field and the environmental conditions experienced on board ships.footnote

5.1 Accuracy of heading

5.1.1 Static

  • The static accuracy of the heading indication should be within ± 1.0°.

5.1.2 Dynamic

  • The dynamic accuracy of the heading indication or output should be within ± 1.5° in addition to the static accuracy as defined. Periods of oscillation of the error should not be shorter than 30 s under the conditions of various sea states and ship's motion likely to be experienced in ships.footnote

5.2 Follow-up accuracy of the transmission system

The follow-up accuracy of the transmission system should be within ± 1.5°, when the sensor is

rotated at a rate of 20°/s.

6 ELECTROMAGNETIC COMPATIBILITY

The compass system, with regard to electromagnetic interference and immunity, should, in addition

to resolution A.694(17), comply with resolution A.813(19).footnote

7 FAILURE CONDITIONS

An alarm should be provided to indicate a failure of the power supply to the compass system.


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