Compass Adjuster

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"Though pleas'd to see the dolphins play, I mind my compass and my way."

The Spleen Matthew Green 1737

  What is compass adjustment?  
    A magnetic compass should align steadily to the earth’s magnetic field pointing to magnetic north. When the compass is installed on a boat, steel and electric equipment may cause magnetic fields that distort the earth’s field at the compass position. The effects of these onboard magnetic fields on the compass change with the vessel’s heading. The difference of the compass’s north from the magnetic north on the different headings is called deviation.

Compass adjustment is the compensation of 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 remove or reduce the deviation. Correctors may be permanent magnets or soft iron. Correcting the compass in small vessels may also involve siting the compass in a more favourable position.

For various reasons such as design, location and practical expedience, 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.

  Which vessels need their compass adjusted?  
  Good seamanship commends all vessels to have a deviation card for the magnetic compass. 
AMSA’s Marine Orders Part 21 covers the compass requirements of vessels under commonwealth survey whilst the National Standard for Commercial Vessels (NSCV) Part C Section 7 Subsection 7C (replacing The Uniform Shipping Laws (USL) Code 13/6) covers the compass requirements for vessels under state or territory survey. Having a properly adjusted compass is integral to survey compliance.
Yachting federations and insurance companies may also have requirements for a Compass Adjuster's declaration. 
  I have lots of electronic navigation equipment, why do I need a compass?  
The magnetic compass is an essential navigational instrument bringing a sense of direction to a vessel. On the water, knowledge of direction is very important, especially when visibility is lost or visual clues of direction are not available. Properly functioning, the magnetic compass shows the vessel's heading. 
The magnetic compass is independent of  power supply, making it a most reliable navigational instrument.
The compass is a key tool for determining the risk of collision (Colregs rule 7)
Without a properly functioning compass a vessel can not reciprocate her course through the water.
  How long does it take to swing a compass?  
    The time to accurately assess and compensate a compass varies, generally, one hour is sufficient. The time should not exceed two hours. The vessel must leave the quay to manoeuvre around the compass headings (swinging the compass). During this swing, the vessel’s magnetic heading is determined by distant bearings, sun azimuths or other appropriate methods. Compass Adjuster makes use of a GPS compass to determine the vessel's heading. This allows for adjustments to be conducted in poor visibility, be it rain or night time.  
  When does my compass need to be swung?  
    All new buildings should have their compass swung at the completion of sea trials. During a vessel's life, changes may occur that effect the compass performance. Such changes include installation of equipment near the compass, change of compass position and for steel vessels, welding and sandblasting.   
  Can I check the compass myself ?    
Yes, you can check for error in your compass by aligning the vessel on known headings (leads and distant bearings) and noting the compass reading. The CompassAdjuster Pelorus allows for all the headings to be easily checked. Visit the DIY page for instructions and to download the pelorus card that is glued to a CD disc.
  How often does my compass need to be swung?  

The National Standard for Commercial Vessels (NSCV) Part C Section 7 Subsection 7C requires the compass  or compasses to be adjusted at intervals not exceeding four years or at a lesser interval when;

  1. The vessel has undergone repairs or alterations which may affect the accuracy of the compass or compasses.
  2. The vessel has not previously operated from any port or place in 
  3. The compass or compasses of the vessel are unsatisfactory or 

The International Standard (ISO 25862), which replaces most of the compass standards referred to by the NSCV, requires all magnetic compasses to be swung and adjusted no less often than every two years.

For vessels over 100 GRT in commonwealth survey, Marine Order 21 applies and there is no prescribed frequency, however, a compass deviation book must be kept and should the observed deviations exceed 5, the compass is to be swung.

  How much does it cost to have my compass adjusted?  
The cost to have a compass adjusted varies depending mainly on your vessel's location. Compass Adjuster - Australia seeks to reduce the per vessel cost of the adjuster's travel by planning and identifying opportunities. Typical costs for small craft in SE Queensland and SE Victoria lie between $250 and $500. Compass Adjuster - Australia will quote a fixed fee before confirming an adjustment booking. On attending the vessel, the master will be requested to sign an Engagement & Indemnity form. It should be noted that adjusters listed on the Adjusters' page are independent operators who will have their own fee structures and practices.



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