How I adjust your compass 

All adjustments require me to vist to your vessel where we go out "for a boat ride."  I will try my best to accommodate your schedule.

To prepare for your service call

  • Have the required personnel available/on-board, prepared to assist as needed and pre-arranged
  • Boarding/deboarding protocols in place.  If the vessel will not be returning to the original dock you will need to provide me with water taxi service to return to where my car is parked.
  • Verify fuel or refuel if needed
  • Compass must be in working condition and not have any bubbles in it.  To check for proper operation, put a small magnet near the compass to deflect the card about 15 degrees.  Remove the magnet and watch the card.  It must return to the rest position exactly in about 10 to 15 seconds.  If it doesen't, the compass will need repair before the adjustment process
  • Verify that equipment is not seized or painted over   If I am unable to disassemble the equipment at the time of the service, repair or adjustment will need to be rescheduled for another time.  I often see compasses that have been glued in place with caulking.  If this is the case you need to break this seal and clean both the boat and compass before I can complete the adjustment work.

Compass adjusting is as much art as science.  To adjust the compass on your boat, we must take the boat out on the river to swing around in circles.   I will give you a heading to put the vessel on. Then I'll shoot a relative bearing on a distant object, using my polaris, and then compare the result to what the bearing should be.  The difference is compass deviation.  We will repeat this process for all four cardinal points of the compass.  From that point I will begin to add equal and opposite magnetism around your compass, continuing to take bearings, until I am able to remove as much of the error as possible.  Large ships require the use of two tug boats and a River Pilot to do the swinging around in circles.

Sometimes I need to mount small magnets to the deck near the compass but in other compasses there are built in magnets that are adjustable to "compensate" for the offending magnetism on your vessel.  After the cardinal points are as "clean" as possible, we will then read the inter-cardinal error and record it.  Only on a steel vessel with inter-cardinal balls is this error adjustable.  So for most vessels I will only record this error, which should be minor, if the cardinal error is mostly eliminated. 

I will provide you with a deviation card laminated in plastic for you to keep at your navigation station to use to correct your course headings to allow for the remaining compass error.

This process normally takes from 1-2 hours per compass.  This is best done early in the morning when there are few other vessels on the river and never on weekends if possible because of river traffic being much increased on weekends.  Of course, fairly good weather and good visibility is a must to get a good compensation of your compass.

I get a nice boat ride and maybe a cup of your coffee, and you get a professionally compensated compass!


Be sure to read my article about Deviation.  Click here: Learn About Deviation