[clpetersen]

Given the historic holiday, I though I would include a bit of history on de-magnitizing, and why it is called degaussing. But if this technique works on your cables, I suggest reading up on the story 'bout how the kings crown was determined not to be pure gold..


Wikipedia:

"The term was first used by then-Commander Charles F. Goodeve, RCNVR, during World War II while trying to counter the German magnetic naval mines that were playing havoc with the British fleet. The mines detected the increase in the magnetic field when the steel in a ship concentrated the Earth's magnetic field over it. Admiralty scientists, including Goodeve, developed a number of systems to induce a small "N-pole up" field into the ship to offset this effect, meaning that the net field was the same as the background. Since the Germans used the gauss as the unit of the strength of the magnetic field in their mines' triggers (this was not yet a standard measure), Goodeve referred to the various processes to counter the mines as "degaussing". The term became a common word.

The original method of degaussing was to install electromagnetic coils into the ships, known simply as coiling. In addition to being able to bias the ship continually, coiling also allowed the bias field to be reversed in the southern hemisphere, where the mines were set to detect "S-pole down" fields. British ships, notably cruisers and battleships, were well protected by about 1943.

Installing such special equipment was, however, far too expensive and difficult to service all ships that would need it, so the navy developed an alternative called wiping, which Goodeve also devised, and which is now also called deperming. This procedure simply dragged a large electrical cable along the side of the ship with a pulse of about 2000 amperes flowing through it. This induced the proper field into the ship in the form of a slight bias. It was originally thought that the pounding of the sea and the ship's engines would slowly randomize this field, but in testing, this was found not to be a real problem. A more serious problem was later realized: as a ship travels through Earth's magnetic field, it will slowly pick up that field, counteracting the effects of the degaussing. From then on captains were instructed to change direction as often as possible to avoid this problem. Nevertheless, the bias did wear off eventually, and ships had to be degaussed on a schedule. Smaller ships continued to use wiping through the war.

To aid the Dunkirk evacuation, the British "wiped" 400 ships in four days.[1]"