Compass Care
Taking time to test, mount and maintain your magnetic compass will keep you going in the right direction
Long-haul truckers and other professional drivers routinely give their vehicles a thorough inspection before pulling onto the street. Lights and signals, horn and brakes, belts and fluids are all checked. As the saying goes, “The life you save may be your own.” Yet, how many of us approach sailing with the same dedication? For some, time on board represents freedom from the rote and mandatory.
Before pulling away from the dock, however, many precautions should be taken, and safety gear—including the magnetic compass—should be checked for availability and dependability.
But, wait a minute. Since when did the compass become a piece of safety gear? After all, a compass is just, well … a compass. You install it, it points north; life is good.
Is that the way you look at the compass on your boat? Chances are it is. Unfortunately, while a magnetic compass is a very simple instrument, there is quite a bit to know about its upkeep and operation. And, not knowing can prove costly, and in some cases dangerous.
Like many things, compasses fail at the worst possible moment. However, they rarely fail without giving the wary sailor
ample warning.
Visual checks First, remove the cover or slide the hood back all the way to see if there is a bubble in the top of the dome. A bubble is not the kiss of death to accurate performance. Small bubbles are little more than a cosmetic distraction. They are, however, a sign of a larger problem—the compass has a leak.
In some cases, the fluid leaks out so slowly that by the time the bubble becomes a nuisance it is time to replace the whole unit. In other situations, the appearance of a bubble could be a harbinger of a seal or diaphragm preparing to give way. Should this happen all at once it would leave compass fluid all over the deck, a pungent smell in the air and the boat without a working compass. Although this rarely happens, when it does the results can carry quite a wallop, especially if you are out at sea or in unfamiliar waters.
Next, 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.
Finally, 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.
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.
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.
Physical checks After a cursory check of the overall condition of the compass, it is time to check for problems in the reliability of its readings.
In order to perform the most meaningful evaluation of a compass’ performance, it should be removed from the dash or pedestal and taken to a location—off the boat is best—away from any magnetic or electromagnetic influences.
First, we will want to do a free-spin test of the compass. Slowly rotate the compass 360 degrees at a relatively constant speed. The compass card will move slightly as inertia carried through the compass fluid pulls it along. Barring the effects of this slight drag, however, it should maintain its original orientation. Once this has been done, perform the test again, this time turning the compass in the opposite direction. In defective instruments, the card may stick slightly for a second or two, then free itself through inertia or when the force of the magnets becomes great enough to pull the pivot back onto a smoother portion of the partially pitted jewel.
The next step is the deflection test. In the first test, the compass bowl is turned around the compass card. In deflection testing, the card is turned within the compass.
Start by verifying that the card is still and that the lubber line is directly on one of the graduations on the card. Then, use a large screwdriver or magnet to slowly pull the card off the mark by 30 degrees. Hold it at 30 degrees for about five seconds and then quickly remove the screwdriver or magnet. Placing it behind your back will usually be sufficient to negate its magnetic influence.
The compass card will then start swinging back toward its original position. In smaller compasses, the card may simply ease back to its original position and stop. On larger instruments, such as the 71/8-inch standards by Ritchie or Baker-Lyman, or the huge 8-inch spherical compass by Danforth, the card should swing past the mark, reverse and settle in on the mark. In either case, if the compass settles on a position even 1.5 degrees from its starting point, or if the card sticks, even for a couple of seconds, you will have reason to consider repairing or replacing the instrument.
If the compass is sticky and does not spin freely, the reason is probably one of the following:
1. The compass card is rubbing against the bowl or gimbal in spherical models.
2. The pivot is dull or malformed.
3. The jewel is pitted.
4. The original compass fluid has been replaced with something more viscous.
5. Any combination of the above.
In any event, the instrument will need a trip to the shop if repairs are cost effective, or a trip to a chemical waste station if not.
Repair or replace The old saw, “If it ain’t broke, don’t fix it,” does not apply here; you just never know when a compass will make the leap from being a marginal performer to a paperweight.
A few years ago, a customer asked that I give his compass a thorough “going over.” He was going to be spending a couple of months in Mexico and planned to sell his boat upon returning to the States. Consequently, he did not want to buy a new compass, nor even pay for a repair, if the instrument was going to be able to hold up for “just another year.” During the test, I noticed it was a bit sluggish, but after repeating the tests just described three times, I concluded that the instrument would undoubtedly hold up for another year—perhaps much longer.
Three days later our compass adjuster brought a compass into the shop and asked, “What do you think about this?” As he asked, he spun the compass slowly in his fingers. The compass card was as locked up as if it had been glued to the pivot. When I told the adjuster that the instrument was obviously shot, he told me it was the same one I had blessed with another year of life just three days prior. This could have happened to anyone. The key is in not allowing it to happen to you. When your compass starts showing signs of stickiness, replace it, or have it repaired at once.
Another point to make is that sticky compasses cannot be “swung.” Compass adjusting is a fine art. Once a compass has been adjusted, the adjuster leaves behind a deviation card bearing his name and placing his credentials in the industry on the line. Only the most inexperienced adjusters would try to adjust a compass that was not in good working order. That being the case, it is not uncommon for an adjuster to arrive on the scene, find an instrument that needs to be repaired or replaced and then increase the amount of his final invoice to cover his second appointment, additional mileage and stand-by time. When this happens, the boat owner gets a lesson in what it means to be “penny-wise and pound foolish.”
Pointers on buying new If you know the compass being replaced is the one that came with the boat, then a wise decision would be to replace it with the same or a similar model. You might certainly choose to upgrade in quality, but you would not want to vary size and sensitivity a great deal. Boat builders are not prone to throwing compasses on their products with no concern for how they will be used. Large compasses will not respond quickly enough for fast moving boats and small compasses can be hard to read from the distances required on larger yachts. In short: One size does not fit all.
If there are any doubts, they can usually be soothed by speaking with a competent compass dealer or by referring to a manufacturers’ catalog.
Even the best companies produce a defective unit from time to time. However, while reputable dealers will replace faulty instruments on request, there is no need to take one to your boat in the first place, considering you can usually test the compass before laying your
money down.
Just about everyone is willing to perform a cursory visual check on a prospective compass. Few, however, are eager to pull a compass off the shelf and perform the free-spin or deflection tests, feeling that doing so would make them look foolish. In today’s market, however, where production short-cuts are the name of the game, spending two or three minutes testing a compass before taking it from the store is apt to make the tester look more like a conscientious consumer than
a fool.
Installation Knowing that you have brought an accurately working compass back to the boat should be a relief. Even so, it is not time to let your guard down. There are still important points to consider.
The first is mounting the compass. If you are the original owner of the boat and are replacing the unit with an exact or similar model, chances are you will not need to make any modifications. However, if you have opted for a different model, or you want to install the instrument in a new location, two issues must be addressed. First, the fore and aft axis of the compass must be parallel with the centerline of the boat. The compass may lie on or near the centerline, or near the boat’s outer edge. But, if the fore and aft axis, i.e. the lubber line, are not on a line parallel to the centerline of the boat, readings will be uniformly incorrect.
The second concern involves placing the compass in a location where it will have minimal interference from magnetic and electromagnetic influences such as motors, tools, speakers, radios, electrical cables or even aerosol cans—anything with a magnetic pull. This would include electrical devices that are used only on occasion, as any change in magnetic field near the compass will have an affect on it.
With these influences minimized, the compass adjuster will have little difficulty in swinging the compass and presenting you with a dependable deviation card.
