What is Compass Adjustment?
Compass Adjustment is the method of analyzing and compensating for deviating forces of a vessel’s magnetic compass. A magnetic compass should always align steadily to the earth’s magnetic field, pointing to magnetic north. However, steel, electronic instruments or equipment, and even the type of cargo carried, can cause the compass needle to point away, or deviate, from magnetic north. Compass adjustment is necessary to compensate these deviating forces with correctors. The deviations on principle headings, typically the cardinal (N, E, S & W) headings and intercardinal (NE, SE, SW & NW) headings are identified, and then correctors are employed to either completely remove or reduce the deviation. Correctors may be permanent magnets or soft iron, which are placed adjacent to the compass. This creates equal, but opposing magnetic fields, thus nullifying the deviating fields around the compass, enabling it to align correctly. Now, the earth’s magnetic field can pass through the compass without being deflected out of its normal path. For various factors such as design, location and the vessel’s unique magnetic properties, all the deviation may not be removed. The residual deviation is recorded on a deviation card as a table or a curve of deviation against the compass headings.
Why is it needed?
Electronic Navigational Aids, or Global Navigation Satellite Systems such as GPS, are vulnerable to loss and error, both intentional and unintentional. Malicious jamming of GNSS signals is a very real threat. Since GNSS is owned and controlled by the U.S. DOD, GPS signals can be terminated or corrupted by the US military for security purposes. In some areas of the world, particularly in the higher latitudes, there may be problematic or no GNSS/GPS coverage, not to mention its dependency on a reliable power supply.
SOLAS Chapter V, Regulation 19, paragraphs 2.1.1, 2.1.2, 2.1.3 and 2.2.1 lay down the requirements for all ships (excluding fishing vessels and pleasure crafts under 150 gt) to be fitted with a magnetic compass or other means to determine and display the vessel’s heading independent of any power supply. They must also be fitted with a pelorus, or other means, to take bearings over an arc of 360° of the horizon and a means for correcting heading and bearings to true north at all times.
The magnetic Compass is required under Chapter V, regulation 19, of the 2000 amendments to 1974 the International Convention for the Safety of Life at Sea (SOLAS), 1974. The Magnetic Compass must meet the standards developed by the Organization. According to Merchant Marine Circular No. 138, these guidelines apply to all ships irrespective of size, and navigation area.
- Navigational safety/Electronic Navigational Aid failures
Our Compass Adjuster
Captain Mike Lepree: Capt. Mike Lepree is a Marine Surveyor with over 10 years of experience performing Compass Adjusting services. He became a qualified Compass Adjuster by going through the required apprenticeship and learning the principles of compass adjusting and its importance in marine navigation at sea.
Portable Gyro Compass Vertical Force Instrument
Pelorus (Azimuth Circle) Stray Magnetic Field Gauge