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5 STANDARDS FOR MAGNETIC COMPASSES

5.1 DEFINITIONS 

5.1.1 A magnetic compass is an instrument designed to seek a certain direction in azimuth and to hold that direction permanently, and which depends, for its directional properties, upon the magnetism of the earth.

5.1.2 The standard compass is a magnetic compass used for navigation, mounted in a suitable binnacle containing the required correcting devices and equipped with a suitable azimuth reading device.

5.1.3 The steering compass is a magnetic compass used for steering purposes mounted in a suitable binnacle containing the required correcting devices.

Note: If the transmitted image of a sector of the standard compass card of at least 15° to each side of the lubber mark is clearly readable for steering purposes at the main steering position, both in daylight and artificial light according to 5.7.1, the standard compass can also be regarded as the steering compass.

5.2 COMPASS CARD ^

5.2.1 The compass card shall be graduated in 360 single degrees. A numerical indication shall be provided every ten degrees, starting from North (000° ) clockwise to 360° . The cardinal points shall be indicated by the capital letters N, E, S and W. The North point may instead be indicated by a suitable emblem.

5.2.2 The directional error of the card, composed of inaccuracies in graduation, eccentricity of the card on its pivot and inaccuracy of orientation of the card on the magnetic system shall not exceed 0.5° on any heading.

5.2.3 The card of the steering compass shall clearly be readable both in daylight and artificial light at a distance of 1.4 m. The use of a magnifying glass is permitted.

5.3 MATERIALS ^

5.3.1 The magnets used in the directional system and the corrector magnets for correcting the permanent magnetic fields of the ship shall have a high coercivity of at least 11.2 kA/m

5.3.2 Material used for correcting induced fields shall have a low remanence and coercivity.

5.3.3 All other materials used in the magnetic compass and in the binnacle shall be non-magnetic, so far as reasonable and practicable and such that the deviation of the card caused by these materials shall not exceed , where H is the horizontal component of the magnetic flux density in m T (micro Tesla) at the place of the compass.

5.4 PERFORMANCE ^

5.4.1 The magnetic compass equipment shall operate satisfactorily and remain usable under the operational and environmental conditions likely to be experienced on board ships in which it is installed.

5.5 CONSTRUCTIONAL ERROR ^

5.5.1 With the compass rotating at a uniform speed of 1.5° per second and a temperature of the compass of 20° C ± 3° C the deflection of the card shall not exceed , if the diameter of the card is less than 200 mm. If the diameter of the compass is 200 mm or more, the deflection of the card shall not exceed ; H being defined as in sub-paragraph 5.3.3.

5.5.2 The error due to friction shall not exceed at a temperature of 20° C ±  3°C; H being defined as in sub-paragraph 5.3.3.

5.5.3 With a horizontal component of the magnetic field of 18m T the half period of the card shall be at least 12 seconds, after an initial deflection of 40° . The time taken to return finally to within ± 1° of the magnetic meridian shall not exceed 60 seconds after an initial deflection of 90° . Aperiodic compasses shall comply with the latter requirements only.

5.6 CORRECTING DEVICES ^

5.6.1 The binnacle should be provided with devices for correcting semicircular and quadrantal deviation due to:

1. the horizontal components of the ship's permanent magnetism;
2. heeling error;
3. the horizontal component of the induced horizontal magnetism;
4. the horizontal component of the induced vertical magnetism.

5.6.2 The correcting devices provided in sub-paragraph 5.6.1 shall ensure that no serious changes of deviation occur under the influence of the conditions described in paragraph 5.4 and particularly considerable alteration of magnetic latitude. Sextantal and deviations of higher order shall be negligible.

5.7 CONSTRUCTION ^

5.7.1 Primary and emergency illumination shall be so that the card may be read at all times. Facilities for dimming shall be provided.

5.7.2 with the exception of the illumination, no electrical power supply shall be necessary for operating the magnetic compass.

5.7.3 In the case where an electrical reproduction of the indication of the standard compass is regarded as a steering compass, the transmitting system shall be provided with both primary and emergency electrical power supply.

5.7.4 Equipment shall be constructed and installed in such a way that it is easily accessible for correcting and maintenance purposes.

5.7.5 The compass, binnacle and azimuth reading device shall be marked in accordance with paragraph 4.6.3.

5.7.6 The standard compass shall be suspended in gimbals so that its verge ring remains horizontal when the binnacle is tilted up to 40° in any direction, and so that the compass cannot be dislodged under any condition of sea or weather. Steering compasses suspended in gimbals shall meet the same requirements. If they are not suspended in gimbals they shall have a freedom of the card of at least 30° in all directions.

5.7.7 Material used for the manufacture of magnetic compasses shall be of sufficient strength and of such a standard as to ensure the elimination of distortion and the maintenance of tolerances for clearances and freedom of movement so as to maintain satisfactory operation in temperatures of -30° C to 60° C.

5.8 POSITIONING ^

5.8.1 The magnetic compass equipment shall be installed if practicable and reasonable on the ship's centreline. The main lubber mark shall indicate the ship's heading with an accuracy of ± 0.5° .

5.8.2 The standard compass shall be installed so that from its position the view is as uninterrupted as possible, for the purpose of taking horizontal and celestial bearings. The steering compass shall be clearly readable by the helmsman at the main steering position.

5.8.3 The magnetic compasses shall be installed as far as possible from magnetic material.

The minimum distances of the standard compass from any magnetic material which is part of the ship's structure shall be in accordance with the following diagram which gives general guidelines to indicate the minimum desirable distances from the standard compass.

The minimum desirable distances for the steering compass may be reduced to 65 per cent of the values given by the diagram provided that no distance is less than 1 m. If there is only a steering compass the minimum distances for the standard compass shall be applied as far as practicable.

Diagram

Enlarge  Image

5.8.4 The distance of the magnetic compass from electrical or magnetic equipment shall be at least equal to the safe distance specified by the manufacturer for the equipment.

5.9 INTERNATIONAL STANDARD ^

5.9.1 The International Maritime Organization Resolution "A.382(X) Magnetic Compasses Carriage and Performance Standards" is the adopted standard.

5.10 EFFECTIVE DATE ^

5.10.1 This Standard comes into force on 1 September 1985.

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