An Improved Instrument for Determining the Positions of Vessels at Sea, and for Laying Off Courses and other purposes.
Year: 1894

page_text: Date of Application, 24th Nov., 1894-Accepted, 15th June 1895
COMPLETE SPECIFICATION.
An Improved Instrument for Determining the Positions of Vessels
at Sea, and for Laying Off Courses and other purposes.
We DAVID JAMES JENKINS of 1 Whittington Avenue in the City of London
Master Mariner and SAMUEL CAREY of Kingswear in the County of Devon
Master Mariner do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement :-
The object of this invention is to enable mariners to ascertain the position of a
vessel at sea, and when a vessel's position is known, to lay on the chart a course to
be steered in order to arrive at any desired point and to ascertain the compass
error or deviation due to the construction of the ship. Now according to this
invention we provide a square constructed of metal, celluloid or any other suitable
material and at the inner angle of the square we pivot thereto a graduated dial or
circle also of metal or other suitable material having the outer face marked
similar to an ordinary compass card. The dial is capable of being clamped to
the square by means of a screw or other clamping device to prevent it from
rotating.
At the centre of the dial is pivoted an arm of metal or other suitable material
having a longitudinal slot therein and provided with a fine wire moving over the
graduations on the dial to enable the position of the arm to be read off and also to
allow the arm to be placed in any desired position we provide also a clamping
screw or other device to enable the arm to be secured to the dial.
The pivot on which the dial and arm rotate is pierced with a hole in the centre
of the circle through which a needle or pencil point may be passed to mark off on
the chart the vessel's position or having found the position to enable the centre of
the dial to be readily placed over the said position when laying off a course.
And
in order that our said invention may be fully understood we will proceed to explain
the same with reference to the accompanying sheets of drawings in which
Fig. 1 represents an instrument for finding the position of a vessel at sea and
laying off courses constructed according to this invention.
Fig. 2 represents the instrument in use on a chart for determining the position of
a vessel.
The same letters denote the same part in both figures.
a is a square to which is pivoted on the upper side a dial b. This dial is marked
with the ordinary compass points and the circumference is divided into 360° every
tenth degree only being marked on the drawing. Or the dial may be divided into
degrees and minutes or any fraction of a degree or of a circle as may be most
convenient is an arm pivoted to the dial in such a manner that the dial and arm
are capable of being rotated independently of each other d is a fine wire stretched
across the aperture e in the arm to allow of the position of the arm being read or
adjusted is a longitudinal slut in the arm the said slot and the wire d being in the
same straight line g is a clamping screw to clamp the arm c to the dial b. i is a
washer resting on the dial b and a clamping screw by means of which the washer
may be made to clamp the dial b to the square a. We prefer to form the clamping
Ecrews with wing nuts the said screws being secured to the square.
kis a small hole through the pivot to admit a needle or the point of a pencil to
enable the instrument to be placed on the chart with the centre of the dial over
any desired spot.

page_text: The instrument or any portion thereof may be made of metal vulcanite, celluloid,
or other suitable inaterial.
A series of parallel lines m in called "meridian" lines are marked on the two
legs of the square perpendicular to the edges thereof and if desired a series of
lines nn parallel to the edges of the square may be added.
The method of using the instrument to determine a vessel's position is shewn by
Fig. 2 which represents the instrument in use with a chart to determine the position
of a vessel entering the port of Stavanger the instrument being supposed to be
transparent for the sake of clearness.
Cross bearings having been taken from the compass on deck and the bearings of
Majoren, Ploentngen, Tyveholm and the Naval Yard ascertained the instrument is
placed on the chart and the dial turned until the N point of the dial is as many
degrees or fi actions of a degree right or left of the inner vertical edge of the
square (which edge must always be kept parallel to the meridian lines on the
chart) as the variation of the compass for the particular place and year. If there
is any compass deviation due to the direction in which the ship's head lies this must
also be allowed for viz. If the compass variation is W and the deviation also W
the leviation must be added to the variation so that the total compass error may
be set off on the dial if the deviation is E and the variation W the deviation must
be subtracted from the variation (if the deviation has not been allowed for in
taking the compass bearing) and the dial set according to whether the variation or
deviation predominates. The instrument may be used in any position so long as
the vertical edge of the square is parallel to the true meridian and the arm is free
to mark out the bearing. In Fig. 2 the deviation of the compass is 0° and the
variation 16° 45' W consequently the dial is turned until the N point is 16° 45' to
the left of the vertical edge of the square this may be done by rotating the
dial until the S point is 16° 45' to the right of the vertical edge as shewn. The
dial is now clamped and the arm rotated until the wire d is over the graduation SE
by EE which is the ascertained bearing of Ploentingen. The arm is secured
in this position by the clamping screw g and the instrument moved over the chart
(keeping the vertical edge of the square parallel to the meridian lines m m one
of which should always coincide with the true meridian) until the slot in the
arm is over the spot on Ploentingen on which the bearing was taken the point
of a pencil is placed in the slot and a line drawn from Ploentingen towards the
centre of the dial. The arm is then unclamped and adjusted to the bearing on
say the Naval Yard again clamped and another line drawn, the intersection of the
lires will give the position of the vessel.
Placing the centre of the dial over the intersection of the lines and still keeping
the inner edge of the square parallel to the meridian the other bearings may be
found and lines drawn the intersection of which at the point of crossing of the
two lines first laid down prove the correctness of the work.
-
To lay off or determine a course dial is turned until the total compass error
(viz. the variation + or the deviation due to position of ship's head E or W of the
true meridian) on the dial coincides with the inner vertical edge of the square.
The dial is clamped in this position the hole in the centre of the dial placed over
the ascertained position of the vessel as marked on the chart. The vertical edge
of the square is next placed parallel to the meridian and the arm brought over the
desired course as found from the chart when the reading of the dial as shewn by
the wire d indicates the course to be steered.
The compass error may also be found by taking three bearings of lights or
other objects by means of the compass on deck. Two of these bearings are laid
off as true bearings and their intersection marked on the chart. The centre of the
dial is then placed exactly over the intersection of the lines and the arm brought
over the third bearing (the inner edge of the square being parallel to the meridian)
and clamped. The dial is now turned until the ascertained compass bearing is
under the wire d the compass error is the distance in degrees of arc of the N point
of the dial from the inner edge of the square E or W.

page_text: Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what
we claim is :—
1. In an instrument for determining the position of a vessel at sea and for laying
off courses the combination of a square of metal or other suitable material with a
graduated circle or dial also of metal or other suitable material pivoted thereto
at the inner angle thereof and a device for clamping the said dial to the square
all substantially as herein before specified and for the purpose stated.
2. In an instrument for determining the position of a vessel at sea and for laying
off courses the combination of a square of any suitable material having a graduated
circle, dial or compass card pivoted thereto at the inner angle thereof with a slotted
arm also pivoted thereto and clamping devices all substantially as hereinbefore
described.
3. In an instrument for determining the position of a vessel at sea and for laying
off courses the combination of a square a a dial or compass card b and a slotted
arm e the said dial and arm being pivoted to the square but capable of independent
rotation substantially as herein before specified.
4. The construction of an instrument for laying off courses and determining the
position of a vessel at sea substantially as herein before described and shewn by the
drawings hereunto annexed.
Dated this 24th day of November 1894.
THOS. E. HALFORD,
11, Furnival Street, London, E.C., Agent for Applicants.