AN IMPROVED METHOD OF DEMAGNETIZING IRON SHIPS AND COMPOSITE VESSELS SO AS TO PREVENT THE DEVIATION OF THE COMPASSES
Year: 1879

page_text: LETTERS PATENT to Evan Henry Hopkins, of Holy Trinity Vicarage,
Richmond, Surrey, Clerk in Holy Orders, for the Invention of "AN IMPROVED
METHOD OF DEMAGNETIZING IRON SHIPS AND COMPOSITE VESSELS SO AS TO
PREVENT THE DEVIATION OF THE COMPASSES."
PROVISIONAL SPECIFICATION left by the said Evan Henry Hopkins at the
Office of the Commissioners of Patents on the 6th August 1879.
EVAN HENRY HOPKINS, of Holy Trinity Vicarage, Richmond, Surrey, Clerk in
Holy Orders. "AN IMPROVED METHOD OF DEMAGNETIZING IRON SHIPS AND
COMPOSITE VESSELS SO AS TO PREVENT THE DEVIATION OF THE COMPASSES."
This Invention relates to a new mode of removing the magnetism in the iron of
ships. It is applicable to iron, steel, or composite vessels, and not only to the
beams, ribs, plates, and other portions of the ship's framework and hull but also to
the steering gear, masts, davits, stanchions, or indeed any masses of iron that may
be in the vicinity of the compasses.
The method here sought to be patented consists in passing one or more straight
electro-magnets or powerful permanent magnets, held more or less in the angle of
the magnetic dip, over the surface of the deck and immediately over the iron beams
from end to end of each beam.
It may be necessary to do this more than once according to the amount of
magnetism to be removed.
Should the operation be carried too far so that magnetism of an opposite
character is induced in the beam the current is changed or the electro-magnet is
reversed so as to have the opposite end presented to the beams, and thus the
magnetism is completely removed.

page_text: Sheets or plates of iron forming part of the deck are treated in the same
manner.
Those portions of the ship's framework that are in a vertical position are sub-
mitted to the same treatment, but it is found necessary in these cases to assist the
demagnetizing influence by causing a vibration through the iron. This is
effected by hammering those portions whilst they are under the influence of the
magnet.
The stern post and rudder head may be demagnetized by holding the magnet or
magnets over the end of the stern post or rudder head whilst a vibration is caused
through the iron by hammering or otherwise. The whole ship may be demagnetized
by extending the process.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Evan Henry Hopkins in the Great Seal Patent Office on the 6th
February 1880.
EVAN HENRY HOPKINS, of Holy Trinity Vicarage, Richmond, Surrey, Clerk in
Holy Orders. "AN IMPROVED METHOD OF DEMAGNETIZING IRON SHIPS AND
COMPOSITE VESSELS SO AS TO PREvent the DeviatION OF THE COMPASSES."
This Invention relates to a new mode of removing the magnetism acquired during
construction in the iron fraine-work of ships. It is applicable to iron, steel or
composite ships, and not only to the beams, ribs, and other portions of the ship's
frame-work, but also to the steering gear or other masses of iron that may be in
the vicinity of the compasses.
The method here patented consists in passing a straight powerful permanent
magnet, or an electro-magnet A, held more or less in the angle of the magnetic dip
over the transverse beams a and b supporting the decks as shown in the accom-
panying Drawing.
The magnet is passed either from the sides to the centre of the deck, or from the
centre to the sides, or from one side to the other, according to the magnetic
conditions of the iron to be operated upon.
The pole of the electro magnet held nearest the deck always being the same as
that which is found in the iron beams to be demagnetised. For instance, if the
beams are found to draw the north end of the compass needle then the south pole
of the magnet or electro magnet, that is, the end attracting the north, is to be held
nearest the beam, and vice versa.
By the passage of the electro magnet on the deck, and immediately over the
beam, an instantaneous reduction of the acquired polarity is effected. The operation
is repeated until the neutral point is reached, that is, until the beam no longer
influences a compass held within, say, a foot of the beam. The direction in which
the magnet is passed, as well as the particular end or pole presented to the beam,
both depend upon the nature of the magnetism to be removed. For instance, in
the case above supposed the electro magnet with its south pole held downwards
must be passed from the sides of the ship to the centre, (i.e.) from c to d and not
from the centre to the sides. The number of times this process has to be repeated
before the iron is demagnetised will depend upon the strength of the magnet
employed or upon the amount of magnetism to be removed.
It is found in practice that only a portion of the ship's beams need to be
demagnetised, as beyond a certain distance, say 30 or 40 feet, they cease to affect
the compass.
The magnetism in the vertical ribs disturb the compass quite as much if not
more than that of the beams. These portions of the ship's framework are operated
upon in the following manner:—
A series of electro-magnets B, B, linked together so as to form one long magnet,
are suspended over the ship's side and passed along longitudinally backwards and
forwards so as to be brought over the various ribs forming the framework of the
vessel. This is extended not throughout the ship's length but only over that
portion which has an influence on the compass to be set free. The operation is
carried out on each side of the ship. The magnets are so arranged that their
magnetism shall be of the same character as that of the ribs, that is, if the top of
the ribs attract the north end of the needle the upper end of the series of magnets
must also attract the north end of the needle.
In demagnetising an iron vessel it is advisable first to operate on the ribs or
the sides of the sbip. Having removed the magnetism from the ribs the beams can
then be operated upon the more easily.
The effect produced by thus treating the ship's framework is found to be
permanent upon all the hard iron and steel of which it is composed. The magnetism

page_text: will not return unless the vessel is kept in one position for a considerable time and
subjected to the process of hammering. In the event therefore of a demagnetised
ship undergoing considerable repair it would be necessary to repeat the operation
herein described.
And having now described the nature of my said Invention, and in what manner
the same is to be performed, I declare that I claim,-
The improved method, herein before described and shown in the Drawing, of
demagnetizing iron ships and composite vessels so as to prevent the deviation of
the compasses.
In witness whereof, I, the said Evan Henry Hopkins, have hereunto set my
hand and seal, this Twenty fourth day of January, One thousand eight
hundred and eighty.