Why is it essential to swing the compass every 1 to 2 years?
Over a period of time and after certain events, the addition or removal of equipment or the carriage of magnetic cargo such as iron ore, the vessel’s magnetic fields may change, altering the residual deviation of the compass. In some circumstances the changes can be quite dramatic.
New steel vessels will have their compass adjusted when first commissioned. It has been known for a one or two year old vessel to record deviation as high as 30 to 40 degrees, as the residual magnetic fields created during the building process gradually dissipate.
Navigators of sea going vessels are required to observe and record compass error daily whilst on passage. These observations are important, not only for safe navigation, but also to assist the compass adjuster in making an accurate analysis of the causes of deviation, should the compass require adjustment.
National marine agencies specify that commercial vessels have their compass adjusted only by a person qualified and authorised to do so. International standards for magnetic compasses and compass adjusting are governed by the International Organization for Standardization (ISO) and the International Maritime Organization (IMO) SOLAS 74 Convention and HSC Code.
SOLAS CHAPTER V, REGULATION 19.2.1:
All ships irrespective of size shall have:
- a properly adjusted standard magnetic compass, or other means, independent of any power supply, to determine the ship’s heading and display the reading at the main steering position.
- a pelorus or compass bearing device, or other means, independent of any power supply, to take bearings over an arc of the horizon of 360°”.
ISO 25862 : 2009 (E): States that all SOLAS vessels should have their compass swung/adjusted and a new deviation card issued at maximum two yearly intervals. When a new vessel is commissioned, compass deviation on any heading should be no more than 3°. Thereafter, deviation on any heading should be 5° or less.
Vessels transiting the Panama Canal are required by the canal authorities to have had a valid compass deviation card issued within the previous 12 months.
Many maritime authorities and organisations stipulate that the magnetic compass is to be swung and adjusted annually. Prudent mariners and vessel operators will always ensure that the compass is regularly checked and properly adjusted. (Source – Marine Survey & Compass Adjustment).