Compensating a Compass

When installing the compass into the mounting hole, make sure that it's properly centered. A portion of the compensating system protrudes beyond the mounting flange and could be damaged if allowed to come in contact with the bulkhead. Most bulkhead models are furnished with a mounting gasket for waterproof installation. The gasket should be used instead of bedding compound since some bedding compounds contain ingredients that damage the plastic dome.

A built-in correcting magnet system is standard on all compass models. These consist of two sets of magnets fixed to two adjusting rods with slotted ends. The slotted ends should be horizontal before starting the adjusting procedure. A small non-magnetic screwdriver is usually provided for this purpose. Before starting compensation, check the area around the compass to make sure that all material of a magnetic nature is secure and in its sea-going position. Using known courses, charts, buoys or landmarks, compensate as follows:
1. Head the boat north and note any error of the compass reading. Turn the  athwartship compensator rod until the compass reads correctly on this
2. Head east by your previously determined course. Observe any error and
correct by turning the fore and aft compensator rod.
3. Head south, note the number of degrees of error and correct for half of
that amount.
  If, for example, on a known south course, the compass reads 170 degrees, turn the athwart ship rod until the compass reads 175 degrees. Head west and correct for half of the observed error as in step 3 above.
  As a rule of thumb, compass compensators are designed to correct for deviation up to twenty degrees. For greater deviation, deck magnets may be used to supplement the built-in correctors. But first check to determine if there is some magnetic influence nearby that could be moved out of the compass field.

  To assure accuracy on all heading,. check for deviation every thirty degrees and record any deviation on a deviation card. We recommend checking at the start of each boating season for changes in deviation.
If you feel that the deviation on your boat is of an unusual nature, the services of a professional compass adjuster will be a wise investment.

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