Author: Deane Hislop
Because the magnetic compass is simple, durable and reliable, it doesn’t always receive the maintenance it deserves. It is tempting to rely solely on modern electronics such as GPS and chartplotters, but unlike those technological marvels, a compass needs no power, has no software and operates when all else fails. As the instrument of last resort, it deserves a prominent spot on your maintenance list. A properly installed and maintained compass should perform faithfully for the lifetime of a boat.
A properly installed compass should be as close as practical to the helmsman’s line of sight. The lubber’s line index mark, which you use to steer, should be parallel to the keel of the boat. A properly installed compass also is placed well away from other instruments and magnetic devices (especially stereo speakers) and shielded from the effects of sun and weather when it is not in use.
Compasses don’t break suddenly. They deteriorate gradually, making problems more difficult to detect. A major cause of external deterioration is constant exposure to direct sunlight on open boats. The dome of an unprotected compass will eventually haze and crack, making what’s underneath it difficult to read, and seals can dry out, allowing fluid to seep through. In either case, the compass is a candidate for repair or replacement.
In addition to gradual deterioration, compasses can be affected by magnetic interference. You can conduct a crude check for this by watching the compass closely while turning nearby instruments on and off — including using the VHF radio in receiving and transmitting modes. Any magnetic interference generated will cause the compass dial to move slightly. Shield or relocate the source of interference to eliminate the problem.
Verify the accuracy of your compass at the beginning of each boating season, especially if other instruments or accessories have been added to the helm area or if substantial changes have been made to the boat. Changes in a compass’s magnetic environment will usually necessitate some adjustment of its internal compensation mechanisms. This is particularly important to remember when buying a used boat. If the previous owner hasn’t had the compass serviced in a while, you should assume that the compass needs to be checked.
Adjustment of the compensation mechanism is a service often left to professionals. But for do-it-yourselfers, compass manufacturer Ritchie Navigation has step-by-step descriptions for two easy compensation methods on its website; visit it at ritchienavigation.com.