From Abracadabra to Zombies
Oct 11 2003
I may have a little insight to confirm your explanation of this off the wall legend. The US Navy as well as other navies has done a great deal of work or magnetism and protecting ships from magnetically triggered devises or magnetic detection devises. At the start of WWII my father joined the group in the Bureau of Naval Ordinance responsible for this work. As a physicist one of his jobs was to write the manual for demagnetizing ships. I know his manual was still in use through the 1950’s.
The techniques can fall into two areas: Reducing the permanent field of the ship and reducing the field induced by the earth’s magnetic field.
To reduce the permanent field the ship is moored over an array of magnetometers to monitor the process. A coil of very heavy gage wire is wrapped around the ship and what amounts to an AC current is passed through the coil. The initial current is quite high and the magnetic field produced could possibly harm some delicate instruments. I know of one instance in which the magnetic drum memory was removed from a computer on board a ship that was to be 'depermed' as it was called then and maybe now. A magnetometer was placed where the memory would have been to determine the strength of the field at that point so that it would be known if it was safe to leave it in place in the future. The current is slowly reduced to zero thus reducing the magnetic field of the ship.
To handle the induced field, various coils are built into the ship. Either by manual settings or automatic controls the current in these coils is varied according to the ships position on the globe and its heading. In some ships such as mine sweepers the currents are even varied in response to the rolling and pitching of the ship.
During the 1950’s experiments were carried out at San Diego to test many of the systems used on the minesweepers. One which might have caused the gullible to think the Navy was a little nuts was done to test the systems that adjusted for the roll of the ship. The ship was moored over a very sensitive array of magnetometers and then further tied down so that is could move only on its roll axis. Canvas water bags were hung along the sides of the vessel to slow the period of it s roll. A pair of platforms was built on the decks, one fore and one aft, to give a set of large flat spaces. Once these preparations were complete the enlisted men of the crew along with some from the shore station that was conducting the test were assembled on the platforms and sent running as a group form side to side to get the ship to roll in a controlled manner. I’m sure some of the sailors must have been convinced that the Navy had gone totally mad.
Grayson L. Wideman
* AmeriCares *