What is a Magnetic Compass, its principle, types and errors?

Advantages of Magnetic compass:

1. No mechanical moving parts.
2. Does not require electrical power.

 Requirements of Magnetic compass

1. At least 1 magnetic compass vessel GRT 150 or more must have 1 spare magnetic compass.
2. If Satellite compass onboard require 1 magnetic compass.
3. If both magnetic compass burnt L/B compass may use.
4. Vessel 500 GRT or over must have gyro compass.
5. To use magnetic compass deviation card is required.

 Limitation of magnetic compass

1. Magnetic compass will not show true north.
2. It will deflected by electric flow.
3. It will deflected by magnetic field.

 Maintenance of magnetic compass

1. Air bubble check
2. Fill up with distilled water and ethyl alcohol mixture.
3. Keep it vibration less dry place.
4. Safe distance from electronic equipment.
5. Dimmer light to be checked.
6. Cleaning.

Positioning of the Standard Magnetic compass

• The standard magnetic compass should, where practicable, be so positioned to maximise its distance from the ship’s magnetic material. While this might be difficult to achieve in respect of the fore end of the bridge or compass deck, the maximum, reasonable, distance should have been achieved e.g. by raising the binnacle on a platform. Any magnetic material which is in the vicinity of the compass should preferably be positioned symmetrically, relative to the compass.
• In ships of unusual design or special purpose, and some small ships, adequate separation of the magnetic compass from magnetic material may not be practicable. The plans submitted at the design stage should include any proposed arrangements, for example, the use of under deck binnacles, and/or the use of non-magnetic materials, intended to minimise the effect of the ship’s structure on magnetic compasses.
• In cases in which the only positions available to site the standard compass are such that, after all reasonable steps have been taken to separate the magnetic compass from magnetic material, significant doubts exist as to the adequacy of the separation, the owner of the ship may be advised that the arrangements will be accepted subject to the performance of the compass in service being reviewed. In order that the review can be made, arrangements should be made for the following information to be supplied to MCA Headquarters:
  1. A copy of the deviation card after each adjustment of the compass.
  2. Sample deviations over a range of latitudes, courses and dates, extending over a period of six months from the date of the first compass adjustment, sufficient to make an overall assessment of the general performance of the compass.
  3. A statement by the Master as to his opinion of the standard compass performance over the six month period described in (b), with comments e.g. whether relevant correctors were adjusted for latitude, etc.

Operational checks of magnetic compass

 The performance of all magnetic compasses, including spares should be checked as follows: