Improved Rule for Laying Off or Reading a Ship's Course on the Chart.
Year: 1893

page_text: Date of Application, 13th May, 1893-Accepted, 8th July, 1893
COMPLETE SPECIFICATION.
Improved Rule for Laying Off or Reading a Ship's Course on the
Chart.
I, ALOYS ROBERT ADOLPH ANTON PAETZELT, of Hamburg, 47, Herrengraben,
Officer on board the German steam-ship Paraguassie 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 :-
This invention relates to an improved ship's rule for shaping or laying off courses
or bearings without using the compass-cards of the sea charts.
The ships rule consists, as shewn by the accompanying drawing (in which
Figure 1 is a top-view and Figure 2 a section of the improved rule), of a semi-
circular protractor a the arc of which is divided into degrees and points like a
compass card. To the stud a³ in the centre of the protractor is pivotted an
alidade e provided with pointers d and e and having attached to its arm c¹ which
projects over the protractor a, a straight edge f, adapted to slide upon the said
arm c¹ in the direction of the length of the latter. The alidade may be fixed to
the protractor in the desired position by means of a set-screw b.
In order to find a ship's course, for instance between two given points A and B
(Fig. 3), it is only necessary to place the instrument on the chart so that one edge
of the straight edge touches or cuts the given points A and B. The protractor a
is then to be moved, when necessary, by drawing the arm c¹ out of the straight
edge f to the nearest meridian of longitude or parallel of latitude on the chart,
as the case may be, until the edge a¹ of the protractor comes in line therewith.
The course marked in this position of the instrument by the pointers d and e
on the graduated are of the protractor is the "true course to steer from A
to B, expressed or given in degrees or points.
"
When the edge al is brought in line with a parallel of latitude, a line due
north and south will not coincide with the said edge, but will be at right angles
with it. Therefore, the reading in such a case must be taken from this point
of the arc as the "true north or the courses shewn by the pointers d and e
must be altered to the left by 90° or 8 points, respectively.
For finding the ship's course the edge a' of the protractor may also be placed
directly upon a meridian of longitude, and then the whole instrument be moved
along on this meridian until one edge of the straight edge f touches or cuts the
given positions on the chart. This obviates the necessity of separating the straight
edge from the arm c¹.
In order to lay or set off a bearing on the chart, the pointer d or e of the alidade
is to be set on the arc of the protractor according to the bearing and to be fixed in
this position by screwing down the set-screw b. Then the edge a' of the instrument
has to be placed to coincide with the most convenient meridian on the chart, and
the whole instrument moved along this meridian until one edge of the straight edge
touches the object of which the bearing had been taken. This edge of the straight
edge f will then give the required line of bearing.
As will be noticed from the foregoing, the construction of this improved ship's
rule is very simple, and its use and management easier than that of parallel or
rectangular rules. It enables also a more accurate reading and setting of course
or bearing angles than it was hitherto possible by using the compass-cards of the
charts only, to obtain.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
An improved ship's rule for shaping or laying off courses or bearings without
using the compass-cards of the sea-charts, consisting of a semicircular protractor a
divided into degrees and points, of an alidade e provided with pointers and adapted
to be fixed at the desired position, and of a straight edge'f sliding upon the arm c¹
of the alidade, substantially as set forth.
Dated this 13th day of May 1893.
PHILLIPS & LEIGH,
22, Southampton Buildings, Chancery Lane, London, W.C.,
Agents for the Applicant.