There shall be appropriate azimuth reading device for the compass of taking bearings.

　

　

There are two different groups of azimuth reading devices to be tested.

　

　

　

　

Group I and II azimuth reading devices shall only be accepted for type - testing in connection with a suitable compass.

　

Where the requirements arid test methods are different for these three groups, the following test methods are also separated (see 4.4.2.5.1, 4.4.2.5.2).

　

The manufacturer shall note, on a separate certificate for azimuth reading devices, his name, and the type and serial number together with the type and card diameter of the compass to which the azimuth reading device belongs (see annex B).

　

Azimuth reading devices shall be clearly marked with the manufacturer's name, type and serial number. Such markings shall also be indicated on the certificate.

　

　

All parts of azimuth reading devices shall be manufactured from non - magnetic material.

　

This shall be tested by exposing the azimuth reading device to a flux density of 2mT along its longitudinal, transverse and perpendicular axes consecutively. After each exposure the azimuth reading device shall be placed on the compass, to which it belongs. When the device is slowly turned on the compass, no discernible deviation of the directional system shall occur.

　

The azimuth reading device shall easily rotate on the compass to which it belongs. No lateral movement which causes a difference in the reading of more than 0,2 °shall be possible.

　

The examination may be carried out by using the card or verge ring graduation of the compass.

　

A spirit level shall be fitted to Group II azimuth reading devices and shall be adjusted in such a way that its zero position indicates the horizontal position of the compass top glass or verge ring within a tolerance of 1°. The use of adjusting screws is allowed.

　

　

The examination may be carried out by comparing the spirit level of the azimuth reading device with a calibrated spirit level placed on the top glass or verge ring.

　

　

4.4.2.4.2 The altitude range covered by an azimuth reading device shall be at least as follows:

　

　

　

The examination may be carried out by means of fixed angle marks on a plumb line or an illuminated vertical slit.

　

　

　

The vertical bearing thread of the object vane and the slit of the eye vane shall be parallel to each other.

　

The examination shall be carried out by observation.

　

The plane of sight defined by the object and eye vanes shall be perpendicular to the top glass or to the verge ring of the compass respectively. In addition the plane of sight shall pass through the rotation axis of the azimuth reading device and shall contain the horizontal bearing thread for card bearings, as well as the index mark for bearings relative to the ship's head on the verge ring graduation.

　

The examination for perpendicularity of the vanes may be carried out by viewing a plumb line or an illuminated vertical slit and by reading the bearing on the graduation. Then the sight shall be turned exactly 180°and viewed again through it in the reverse direction. if the object is still parallel with the vanes and still lies in the plane of sight, the vanes are perpendicular to the plane of rotation. At the same time it is verified that the plane of sight passes through the rotation axis.

　

　

The mirror, if fitted, used to take bearings of high altitude objects shall be attached and adjusted in such a way that the reflection plane is parallel to the plane of sight in any position to within the tolerances given in table 2. If the mirror is of the bilateral type, each of the two mirror sides shall fulfil these requirements. The use of adjusting (correction) screws is allowed.

　

With or without the shades the bearing errors shall not exceed the values given in table 2.

　

　

4.4.2.5.1.5 Prismatic magnifying glass (if any)

When reading card bearings by means of a prismatic magnifying glass, the readings shall not differ from the readings of the horizontal bearing thread by more than 0,3°.

　

The examination shall be carried out by inspection.

　

　

There may be four types of error in a Group II azimuth reading device:

　

a) a collimating lens of incorrect power or placed at the wrong distance from the compass card graduated edge;

b) a prism, the axis of which is not at right angles to the line of sight;

c) a prism the axis of which is not parallel to the plane of the compass top glass;

d) shades that are not optically flat.

　

The collimating lens focal length shall equal 1,12 x the compass card radius and be placed at that distance from the graduations at the card edge.

　

This can be checked in two ways.

　

a) A distant object is correctly aimed. The observer's head is then moved so that the object appears first at one extremity of the field of view and then at the other. The error in the readings should not be more than those in column 2 of table 3.

　

b) A distant object is correctly aimed. The observer's head is held still, and the azimuth mirror is rotated 5°first to one side and then to the other. The errors produced should not be greater than those in column 3 of table 3.

　

　

　

The bearing of a distant object is taken by means of plane sights or any other instrument, for which the error is known. The difference between this and the bearing by the azimuth mirror is compared and shall not be greater than that of column 2 of table.

　

The compass is placed so that the top glass is horizontal. A plumb line at a reasonable distance (not less than 2 m) is sighted accurately. The prism is rotated about its axis. Any change in the bearing shall not exceed that in column 3 of table 3.

　

The card diameter shall be stated in the certificate (see annex B).

　

A distant light, not less than 2 m away is directed by the prism on to the compass card graduations. The shades are then placed in line and in no position should the line of sight be appreciably changed.

　

Adjusting screws are allowed under the prism.

　

A level shall be provided and to an accuracy of 1° (see 3.2.3).

　

The perpendicularity and centring shall be examined visually while rotating both the compass and the pin, while a distant light is producing a shadow.

　

4.4.4 Marking (ISO 449, 4) The following parts shall be marked with the information given and in the position shown in table 1.

　

　

(referred from CIRM: revision of solas chapter V, adjustment of magnetic compasses, NAV 45/Agenda Item 5, May 1999)

　

A magnetic compass shall be kept properly adjusted in order to be relied upon for safe navigation.

　

All magnetic compasses shall be swung and adjusted no less often than every two years, and after every docking or significant structural work.

　

The adjustment shall be carried out by a licensed compass adjuster approved by the Administration.

　

Such adjustment shall include adjustment for all magnetic latitudes in which the ship may operate, so that the residual deviation after any change of latitude following the ship's second periodic swing after new construction does not exceed [2] degrees.

　

Means of correcting residual deviations to provide true headings and bearings shall be available at all times.

　

The adjustment shall be carried out for the semicircular and quadrantal deviations due to (a) the horizontal components of the ship's permanent magnetism, (b) heeling error, (C) the horizontal component of the induced horizontal magnetism and (d) the horizontal component of the induced vertical magnetism using profitable devices respectively.

　

Each magnetic compass is properly compensated and its table or curve of residual deviations shall be available on board in the vicinity of the compass at all times.