Email The Compass Adjuster



Dock Side

With credit to Andrews Compass Service for most of this document

1.  Check alignment of the compass with the fore-aft line of the ship: (A-Coefficient) Pedestal mount sail/ Centerline mounted: Sight the compass center pivot pin, forward lubbers line, and boat mast / bow.  If compass is mounted off of the Centerline: Measure exactly the distance off of centerline, mark the same distance on the bow with a spot of tape and sight the compass to the mark.  All should line up. If not, slew the compass to bring them into alignment with the mast/bow or off center mark.

2.  Check steering system: With chain drive system, turn wheel slowly lock to lock. On any type system, check for change in compass heading caused by the spokes of the steering wheel. IF THE ANSWER IS YES, consult a professional boat repair yard and have the chain and/or/ wheel replaced with non-ferrous stainless steel materials.  Test with a hand held compass before purchase and installation.

3.  Check for position of ammeter gauges, tachometers: If they are near the compass, do they affect the compass when the engine R.P.M.'s are changed? IF YES, consult a professional boat repair yard and have the instruments replaced with a digital display meter or a high quality D'Arsonval meter movement, and then have the compass professionally swung and the deviation noted.  (D'Arsonval meters do not have a variable magnetic signature like the less expensive moving magnet meters sometimes found on boats.)

4.  Check for Electronics, Windshield wiper error: IF YES, a second deviation card is required. A compass can only be adjusted for one set of variables; i.e.,EngineON or Engine OFF, Wipers ON or Wipers OFF, Radar ON Radar OFF. A second or third card can be generated for other variable, but you can only adjust for ONE SET OF VARIABLES

5.  Check dodger bows for effect on compass. IF YES, have dodger bows replaced with non-ferrous stainless steel materials.  Test with a hand held compass before purchase and installation.

6.  Check within 3 (three) feet of the compass in all directions, for miscellaneous ferrous metal objects, i.e., cell phones, binoculars with built in compasses, anchors, stereo speakers, propane tanks, air horns and hand held VHF radios, etc. SECURE ALL ITEMS.

7.  Many of the above problems are correctable, either by relocating the compass or the equipment causing the problem.  Two of the worst offenders are radio speakers (they have a magnet in them) and some types of autopilots. Many depth finders have a built in speaker that can affect the compass.  Check around the compass with a “sniffer” - a small hand held compass, which you observe for movement, as you bring it close to items near the compass.  If you cannot correct these problems yourself, contact the Compass Adjuster for help to resolve the problem, compensate the compass, or determine the deviation at each heading.

8.  When not using your boat, keep the compass COVERED AT ALL TIMES. Use a light colored cover to reflect the UV rays which cause crazing on your plastic dome.

Under Way

1.  Check the compass for error at least once a year after commissioning. Whenever you change anything of a ferrous metal nature or a power supply source (within 3 feet of the compass), the compass should be rechecked.

North/ South (C-Coefficient): Check compass heading off a fixed land range within +/- 6 degrees of N/S

East/ West (B-Coefficient): Check compass heading off a fixed land range within +/- 6 degrees of E/W

NOTE- I recommend using Fixed Land Ranges, because they do not move. The problem with floating Navigational Aids is that you must assume that they are on station and that is not always true. Use caution when checking your compass against Loran or GPS. Both generate a HAS BEEN FUNCTION -  (The course & speed average HAS BEEN 162°, & 6.2 knots). It does not generate real time information. Even if you maintain a steady straight course for a number of minutes you will not be close to the accuracy of fixed land ranges.

2. Upon completion of your voyage, avoid wiping salt water spray off the dome with your hand (it will dull the plastic dome surface), COMPASSES LOVE FRESH WATER BATHS.  If the compass can survive salt water, it certainly will survive a fresh water bath, (as will your sextant and other instruments.)  NEVER LEAVE SALT ON ANY INSTRUMENT for more than a short while.  Never use abrasive cleaners or waxes on the DOME.

Winter Storage and Care

I always recommend that my customers remove their compasses in the winter and store them in a constant temperature environment. In the days gone by when boats where stored at boat yards and professionally maintained, compasses where removed along with electronics and stored in heated locker space. Today more and more boat owners are taking their vessels home or to self service facilities. Keep in mind that a vessel stored outside under cover can reach temperatures in the 60 degree + range during the day, and plummet to freezing temperatures at dusk. Each of these cycles of heating and cooling cause the compass fluid to expand and contract. If there is a crazed or cracked dome, a hardened O-Ring, or worn expansion membrane, you WILL GET A BUBBLE in your compass (It is the path of least resistance).

1. Air bubble indicates need of repair.  It indicates a leak.   Just adding fluid is as effective as adding air to your automobile tires without first having the nail removed from the tire which is the source of the air leak.  It will just leak again.  Sometimes the leak is caused by the fasting screws becoming loosened by vibration, sometimes it caused by a rotting diaphragm and or cracks and crazing in the dome which is caused by a combination of age and sunlight. 

Whenever you get a bubble in your compass, it is an indication of a failure in your sealing system. A bubble in almost all cases requires a trip to the repair shop. Left untended, the bubble (which is air and contains particles of water) will cause contamination of the compass fluid. In the worst case's water droplets can cause pitting of the compass dial and interior paint, which means more $$$$ to repair. Do yourself a cost saving favor, when you get a bubble do not wait to get it repaired.

2.  Check for compass sensitivity: Place the compass on a wooden table, rotating the compass so that North is lined up with the forward lubbers line. Using either a magnet, or a ferrous metal object, (i.e., wrench, hammer, or screw driver,) cause the compass heading to change + & - 15 degrees. Rotate the compass and repeat the procedure for the other three cardinal points (East, South, and West). The compass MUST return to the original heading. If it does not, then the compass pivot & jewel, or dial assembly must be replaced.

3. Note the color of the fluid. Over time, and especially as the instrument is exposed to direct sunlight, the fluid will break down and cause rubber and plastic parts to deteriorate. This will give the fluid a milky or rusty appearance, and in some cases, will cause a dark residue to form on the inner surface of the dome and on the compass card. This problem may be especially annoying in certain models that have a clear disc of Lexan affixed over the compass card. These discs were designed to stabilize the compass card and to aid in checking bearings while standing to either side of the compass. Even so, it still provides two additional surfaces on which residues can collect.

4. Watch for crazing at the base of the dome. As compasses begin to age, stress fractures tend to form—first along the base of the dome and then rising higher and higher along the sides. Sometimes, fractures are large and reflect so much light they are easily noticeable. In such cases, the chance of a problem with leakage is eminent. It is much more common for the fractures to be tiny but appearing in greater numbers. A compass could have many of these tiny stress fractures and perform well throughout its normal lifespan with no trace of leakage. There are times, however, when these myriad fractures will meet all the way around the dome causing it to give way all at once often when accidently bumped.

Note, however, that compasses from C. Plath and lifeboat compasses by the former John E. Hand Company use thick, glass domes. In these instruments crazing is not an issue.

5.  The mariner who gives a bit of attention to his or her compass should never be taken by surprise. In fact, the problems described can be decreased or eliminated by keeping the compass covered when not in use. For not only do ultraviolet rays render the plastic more brittle and susceptible to fractures, but the liquid-filled dome acts like a short-focus lens that can, in bright sunlight, heat the fluid inside to more than 200 degrees Fahrenheit, causing an inordinate amount of pressure to build. This in turn places additional stress on the seals and O-rings, diaphragm and dome.



Suggested Reading

Eldridge Tide & Pilot Book (pg. 62, 201, 224, 1997 Ed.)
Chapman’s Piloting Seamanship & Small Boat Handling (Chapter 14, 1966-67 Ed.)
Dutton's Navigation & Piloting (pg. 84-97, 13th Ed.)