A Protractor or Instrument for Compensating for Compass Error when Laying Off Courses in Navigation.
Year: 1899

page_text: Date of Application, 1st June, 1899-Accepted, 15th July, 1899
A Protractor or Instrument for Compensating for Compass Error
when Laying Off Courses in Navigation.
I, SAMUEL WALKEY GILLETT, Chartered Patent Agent, of the Firm of H. B.
Barlow and Gillett, 17, St. Ann's Square, Manchester, in the County of Lancaster,
do hereby declare the nature of this invention, which has been communicated to
me by John Wight Livingstone, Commander of the s.s. "Dwarka," British India
Steam Navigation Company, Bombay, 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 a protractor or instrument for compensating for com-
pass error when laying off courses in navigation and so simplifying the applica-
tion of compass error to the true course as indicated by the chart.
In the accompanying sheet of drawings,-
Figure 1 is a plan, Fig. 2 an edge view and Fig. 3 a transverse section of a
protractor made according to this invention. Fig. 4 is a plan illustrating the
practical application of the instrument.
In these views, a designates the base-plate of the instrument which is made
preferably of metal in the form of half a circle of say about eight inches in
diameter. On the base-plate a is fitted a sliding semi-circular protractor scale b
which is slotted at 61 and is secured to the plate a by a screw e provided with a
milled head or by any other suitable means. The protractor scale b is graduated
with duplicate scales the degrees starting from zero at each end and reading up
to ninety in the middle or bisecting line of the semicircle.
The instrument when in use is placed on the chart on the line of the true
course to be steered with the centre of the circle marked A on the meridional
line N, S, the degrees on the outer circle where they intersect this line being the
true course to be made by the ship. The protractor scale is then moved to the
right or left according to the number of degrees of compass error to be applied
easterly or westerly as the case may be, the arrows on the instrument indicating
the direction in which the protractor scale must be moved in order to compen-
sate for the compass error, then the line intersecting the meridional line when
drawn through the two ends of the protractor scale after the error has been
applied indicates the compass course to steer. The example illustrated by Fig. 4
indicates the application to compensate for ten degrees of compass error.
-
The chief advantages obtained by the use of this instrument are as follow:.
First, Any mistakes arising from mental calculation are obviated. Secondly,
-the error cannot be applied the wrong way so long as the directions on the
instrument are followed, and-thirdly, the true course and the compass course
are both given by the one instrument before it is removed from the chart.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what I
claim is:
1. The construction use and application of a protractor or instrument consist-

page_text: ing of a semicircular plate provided with a sliding scale substantially as and for
the purposes herein set forth.
2. The combination with the semicircular plate a, of the semicircular pro-
tractor scale fitted to slide thereon substantially as and for the purposes herein
described and as illustrated by the accompanying drawings.
Dated this 31st day of May 1899.
H. B. BARLOW & GILLETT,
Agents for Applicant, 17, St. Ann's Square, Manchester.