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Degaussing ships?

  1. Sep 25, 2004 #1
    Degaussing ships??

    Does anyone know how ships are degaussed exactly? I know that basically very thick electrically conducting cables are wrapped around perpendicular to length of the ship. Large currents are then sent through in an effort to cancel out the ships magnetic field.

    If anyone knows anything more bout this, I would appreciate any input.

    BTW: Didnt the Philidelphia Experiment work in a similar manner to this?
  2. jcsd
  3. Sep 25, 2004 #2
    How does the ship get the magnetic field in the first place?
  4. Sep 25, 2004 #3


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    The ship gets magnetized by moving across the earth's magnetic field. As the "lines of force" cut through the iron of the ship's hull, they generate Em fields which shown up as "induced magnetism". This was a problem when iron ships were first used in the 19th century; their magnetic compasses were thrown off by the magnetism. They had to correct for it by piutting large masses of soft iron near the compass to correct the field. You can see these in old pictures of the "binnacles" or compass stands they used; the two spheres on either side of the compass are iron for correction, and more iron bars hang inside the case, and can be adjusted to "tune" the effect.

    In world war II the axis used torpedos that could home on this induced magnetism. So the allies tried to remove the magneism by wrapping electric cables around the hull and running current through it. Properly tuned it would cancel out the induced magnetism.

    Yes I beleieve the USS Philadelphia was one of the ships in which this degaussing was tested, and that may have contributed to the silly myth that goes by the name Philadephia experiment.
  5. Sep 26, 2004 #4
    self, that's a great WW2 story. Do you have reference for Axis powers producing a magnetically steered torpedo ? A reference to Allied ship with wires wrapped around it ?

    This was not common practice. The U boats were point and shoot.
    And that worked for about 25000 ships sunk. Some kinda experiment you reference ? "Properly tuned it would cancel out the induced magnetism". Sure.

  6. Sep 26, 2004 #5


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    It may not have been common in WWII, but it certainly is today. Virtually all Navy ships are equipped with it. Minesweepers go a step further - they aren't made of metal.
  7. Sep 26, 2004 #6


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    How sure you sure about this? Seems a History channel show I was watching recently said otherwise.
  8. Sep 26, 2004 #7


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    There were certainly magnetic mines in WWII. My dim memories are that the Japanese had long range torpedoes with magnetic fuzes.
  9. Sep 27, 2004 #8


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    The torpedoes or not "magnetically steered", they were magnetically detonated. Like many of the mines of that time, torpedoes and proximity fuses set to detect the presence of a nearby metal object by the magnetic field given off by that object. This allowed torpedoes to be said to adapt slightly greater than the draw of the ship, thereby assuring that they would detonated underneath the hull, and break the ship's back.
  10. Sep 28, 2004 #9
    Thats great and all, but I asked about degaussing ships.
    As far as I know, magnetic mines detect a ships magnetic field, then it checks the ships *acoustic* signal, if the signal is not registered with the mine as a friendly vessel, KABOOM.
  11. Sep 28, 2004 #10


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    Just a minor knit-pic here, but the ship actually gets magnetized during construction. Building a ship within the earth's magnetic field produces a magnetic signature to the metal of the ship's hull. I'm not sure if this occurs while the iron is melted and then hardens, but it seems likely. I am even told that one can, if one has the proper expertise, determin in which shipyard a particular ship was built by looking at its magnetic signature. The "induced magnetism" is the interaction of the ship's permanent magnetic field with the earth's magnetic field.

    I believe that in the old days (WW II), a charged cable was simply passed along the length of the ship, like keel hauling, to disrupt a magnetic signature. Nowadays, according to this site, ships have permanent coils installed within their hulls.
  12. May 12, 2008 #11
    The Earth's magnetic field contributed to the ship's "magnetic signature" as soon as the keel was laid. Countering all of the forces influencing this signature once the ship was shaken down required constant monitoring of many magnetic coils--which contributed to use of a large portion of the United States' copper suppy by 1943. In fact, such continued large-scale use was discussed by the Bureau of Ships in terms of copper cost versus men lost at this highest levels (I have a copy of the memo from the National Archives). Remember the wartime "steel/zinc" cent? Since then, pennies are copper clad, not all copper..

    Also causisng induced magnetization were the 16 inch guns and ocean waves pounding against the ship, as well is travel away from the point of construction, turns, time since demagnetizing on a "deperming range" (usually not to be longer than 6 months). This was a 24/7 job headed by Naval Lieutenants (equivalent of Army/Marine Captains) although noncom and rate staff were involved. The insulated coils of copper became so hot that a pinprick in the insulation would lead a cursing sailor off to the infirmary with 2nd or 3rd degree burns from spewing molten copper. This information comes from many sources, but primarily my Dad, who was an undergrad/grad Physics night student during the War working for the Bureau of Ordnance, USN by day. BTW, the Philadelphia Experiment is purely myth.
  13. Aug 11, 2008 #12
    Re: Degaussing ships??

    The Eldridge was specially modified, probably had its gun turrets replaced with special generators in reverse the idea was to suck the electrons out the ship. Removing the electrons changes the way light/radar interacts, gold is a very good conductor and it reflects very well too... glass is a poor conductor of electricty and it is clear, the difference is electron drift of the atoms of gold and silicon. So if the Philidelphia Experiment did take place I believe this is what they were up to.
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