[QUOTE=dnv;401737] Hi there
My Suunto (see attached picture) deviates from 5 to 12 degrees, depending on the true heading. The compass has little magnets underneath for compensation.
I found advice on howto compensate here and there:
Ritchie Navigation - Compass Compensation
Does anybody on here have other, maybe more simple, advice?
thanks for any help in advance, Jan [/QUOTE
Compass deviation is the error introduced by external influences such as ferrous metal components, magnetic materials or electrical cables which are too close to the compass.
The proper procedure:
Once all such influences have been minimised the correct course of action is to check swing the compass. Using a calibrated hand bearing compass take readings from a position about 10 meters in front of the bow, looking down the centreline from the bow to the stern, with someone monitoring the boat compass. Take a reading on the boat compass on 0, 90, 180 and 270 degrees and write down the headings shown on the boat compass. Using the mini magnets, correct these errors remembering that that over correction will cause errors on the reciprocal. Correction with in 3 degrees should suffice.
Now do the same ever 45 degrees. Errors that can't be eliminated are entered on a "compass deviation card" fitted next to the compass. So, for example if there remains a +3 degree error on North, the deviation card will read heading 000 - steer 357 and so on. This card should start 000 and list headings every 45 degrees.
The quick procedure:
Minimise external influences. Using a GPS at slow speed in flat conditions, adjust your headings N,S,E,W and then check every 45 degrees. Remember GPS is true heading so allow for variation in your area. For any remaining small errors, if you wish, you can make up a deviation card as above.
Having said all that, if you can read your compass within 3 degrees at 30 kts in anything less than glass conditions, you're a better skipper than me.