If one is to judge by the impressive demonstration given aboard the Sperry research boat Wanderer when it last visited the Naval Academy, the magnetic compass is still doing very well, thank you.
As is usually the case, meeting the interesting people aboard the Wanderer was an important part of the program. Among the group was Mr. Noel Macy of Washington who mentioned an interesting case of magnetic compass compensation for his yacht by Lieutenant R. G. Willis, U.S. Navy, Retired. The report of the technical difficulties experienced were so well written that it is given verbatim:
“On September 17, 1948, I was called by John Trumpy and Sons to adjust a compass on a 45-foot Annapolis-type cruiser. When I arrived on board the boat, the owner told me that the compass remained practically steady on 240°, no matter how the boat was headed.
“The first thing I thought of was that the compass card might have in some manner jumped off the pivot and become jammed, or that it had a cracked bearing and bent pivot. I had a case of this three years ago, and while I could move the compass with magnets, it moved by jerks and appeared dead; that is, not as if it were freely floating. This compass, however, moved, and moved smoothly, when I tested it with a magnet. It still returned to 240°, though, when I removed the magnet, although the boat was headed approximately southeast.
“At this point the owner told me that the boat had been struck by lightning recently. Believing this might have affected the compass magnets, I removed the compass from its gimbals and took it ashore to test it. On the dock the compass indicated magnetic directions properly and was within the limits of tolerance when given the vibration and sensibility tests.
“Now being certain that the compass was in good condition, I returned to the boat and looked for magnetic material along the line in which the south end of the compass was pointing. I knew it must be in this direction since the compass was mounted on the starboard side of the motor boat with nothing magnetic along the direction in which the north end was pointing.
“The path led toward the galley. In the galley was a small gas range, a five-foot-high steel ice box, and a non-magnetic sink. Using the compass as a detector, holding it at waist level, I walked around the galley and stood in front of each piece of galley equipment without causing any deviation of the compass. However, when I raised the compass to head level—(I’m five feet, five inches tall— the compass pointed to the ice box and stayed pointed toward it regardless of where I moved.
“The top of the ice box was about three feet forward, three feet below, and four feet to the left of the compass. There were two cupboards and a locker between it and the compass which might have been expected to insulate the compass from any magnetic effects, but the fact was that they didn’t.
“After mounting the compass again in its regular position I neutralized most of the magnetic effect of the ice box by using a vertical magnet, taking out all except 10° of the deviation it caused. It required the largest magnet I had in my kit, one six inches long and one-half inch in diameter, to do this. I then proceeded with the compass adjustment, using the usual fore-and-aft and athwart ship magnets. The greatest deviation after adjustment was 3° E on 030° and 3° W on 210°. The compass was normally responsive to changes of heading when the adjustment was completed, introduction of the large vertical magnet not appearing to have caused any abnormal sluggishness.”