Many of today’s boat owners rely heavily on their electronic navigation systems. While it’s nice to have all these high-tech conveniences, in a crisis, every boater needs the old fashioned skills of using a paper chart and compass. Electronic nav instruments are sensitive and can malfunction for any number of reasons. However, if your vessel is equipped with reliable charts and a correctly functioning compass, you can navigate to your destination in safety.
Dockside
Take a moment prior to your next cast-off to give your compass a “health check.” Here’s a step-by-step guide to check the reliability of your compass.
- While at the dock or mooring, check the alignment of the compass on the fore-aft line of the ship (A-Coefficient). With a pedestal mount sail/centerline mounted compass, sight the compass center pivot pin, forward lubber line and the boat’s mast and bow. They should all line up. If not, slew the compass to bring them into alignment with the mast/bow.
- Once you have the compass in alignment, check the steering system. With a chain drive system, turn the wheel slowly lock to lock. On any type system, check for changes in compass headings caused by the spokes of the steering wheel. At this point, if you observe changes, consult a professional.
- Now, take a look around your boat; check the position of amp meter gauges, tachometers and other electronic devices (including your portable GPS). If they are located near the compass, check to see if they affect the compass reading when the engine RPM changes. If so, this is another instance when you will need to consult a professional.
- Check for electronics or windshield wiper error. If you get an error, a second deviation card is required. A compass can only be adjusted for one set of variables, i.e., Engine On or Engine Off, Wipers On or Wipers Off, Radar On or Radar Off. A second or third card can be generated for other variables, but you can only adjust for one set of variables.
- Check dodger bows for any effect on the compass. As in item #4, changes reflect the need for an additional deviation card.
- Check within eight feet of the compass in all directions, for miscellaneous ferrous metal objects, i.e., anchors, stereo speakers, propane tanks, air horns and hand-held VHF radios, and secure all items.
- When not using your boat, keep the compass covered at all times. Use a light colored cover to reflect the UV rays that cause crazing on your plastic dome.
Underway
Once out on the water, you’ll want to check your East/West (B-Coefficient) compass heading off a fixed land range with +/- 10 degrees of E/W. Then, check your North/South (C-Coefficient) in the same manner. 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 GPS. It can generate a “has been function” (i.e. 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. Upon completion of your voyage, avoid wiping saltwater spray off the dome with your hand (it will dull the plastic dome surface) Compasses love fresh water baths! Never use abrasive cleaners or waxes on the dome.
Decommissioning
I always recommend that my customers remove their compasses for the winter and store them in a constant temperature environment. In days gone by, when boats were stored at boatyards and professionally maintained, compasses were removed along with electronics and stored in heated locker space. Today, more and more owners are taking their vessels home or to selfservice 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 heating and cooling cycles causes 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’s the path of least resistance).
This is also a good time to 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. a wrench, hammer, or screwdriver), cause the compass heading to change +/- 4-5 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.
General
Whenever you get a bubble in your compass, it’s an indication of a failure in your sealing system. In almost all cases, a bubble 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 cases, water droplets can cause pitting of the compass dial and interior paint, which can be a costly repair. Do yourself a cost-saving favor - when you get a bubble - Do not wait to get it repaired.
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 six feet of the compass), the compass should be rechecked. With good settings and proper maintenance and storage, your compass is the best piece of navigation on your boat.
Suggested Reading
Eldridge Tide & Pilot (pg. 202 -203, 2009 Ed.)
Andrews Compass Service, located in Mattapoisett, MA, provides adjustment services to government, research, commercial, and recreational vessels throughout Southeastern New England. They offer both Sun Azimuth and Gyro methods of compass adjustments. They are a fully authorized sales and service facility for all major compass manufacturers. Visit andrewscompass.com or call 508-758-3001or (toll-free) 800-KOM-PASS (566-7277). ✦
