Apparatus for Indicating or Correcting a Ship's course at Sea.
Year: 1898

page_text: Apparatus for Indicating or Correcting a Ship's course at Sea.
I, WILLIAM SPINK, of Gordon Villas, West Newgate Street, Arbroath, in the County
of Forfar, Teacher of Navigation, do hereby declare the nature of this invention to
be as follows:-
This invention has for its object the provision of a simple instrument or device by
the use of which the true course of a ship at sea may be indicated, and if need be,
corrected, without making abstruse calculations or referring to voluminous Azimuth
tables, by setting a pointer on the instrument to show at what time any, of the stars
chosen will cross the ship's course or track, the stars chosen being stars that are easily
known by the aid of the invention.
The indicating apparatus comprises a disc of metal, cardboard or other light material
having printed or otherwise impressed on it a diagram on the plane of the Equator on
which the stars are plotted down according to their declinations and right ascensions,
and having lines radiating from the pole to represent the meridians or hour circles.
The first point of Aries, being the point from which the sidereal time is got, is con-
spicuously marked.
The dise is mounted so as to be capable of rotation around its centre on a flat board
whereon are impressed around the edge of the dise two circles or diagrams concentric
with the disc and graduated, the one having 365 divisions to show the days of the
year, and the other having 24 divisions to show the hours of the day and subdivisions
for minutes.
The divisions of the hour circle start at mid-day opposite the division
representing the 22nd day of March, and the division representing mid-night on
the one circle opposite the division of the other circle between 21st and 22nd of
September.
Centred on the same axis as the disc is a pointer representing the mean sun
extending radially outwards towards these circles.
When using the invention the first point of Aries is set to the month and day,
which represents the sidereal time at mean noon at Greenwich on that day. The
sun pointer is then placed at mid-day. By turning round the disc which carries with
it the pointer it will be seen when any star on the diagram will cross the meridian or
due south in the Northern Hemisphere or north in the Southern Hemisphere. If the
ship is on any of these courses the star should be right ahead at the time shown by
the mean sun pointer. For the other points the Azimuth card, which shews the
sidereal time abreast of every point, is needed.
Azimuth tables will be supplied with the revolving diagram and will probably be
on the same ground plan as the year and hour circles. A few small cards or a small
booklet will be all that is required for that purpose, as each star crosses the meridian

page_text: about four minutes earlier every night or day sun time, the sidereal time being
constant in the same parallel of latitude.
Dated this 20th day of June 1898.
Apparatus for Indicating or Correcting a Ship's course at Sea.
I, WILLIAM SPINK, of Gordon Villas, West Newgate Street, Arbroath, in the
County of Forfar, Teacher of Navigation, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
This invention has for its object, the provision of a simple instrument or device by
the use of which the true course of a ship at sea may be indicated, and if need be,
corrected, without making abstruse calculations or referring to voluminous Azimuth
tables, by setting a pointer on the instrument to show at what time any of the stars
chosen will cross the ship's course or track, the stars chosen being stars that are easily
known by the aid of the invention.
The invention is illustrated by the accompanying drawings, Figure 1 being a plan,
and figure 2 a vertical section on the line x-x, of the apparatus for indicating a ship's
course at sea.
The indicating apparatus comprises a disc A of metal, glass, cardboard or other
light material having printed or otherwise impressed on or affixed to it a diagram on
the plane of the Equator on which the stars are plotted down according to their
declinations and right ascensions, and having lines B radiating from the pole to
represent the meridians or hour circles. The first point. C of Aries, being the point
from which the sidereal time is got, is conspicuously marked on the disc A.
The disc A is mounted so as to be capable of rotation around its centre A¹ on a
flat board D whereon are impressed around the edge of the disc two circles or
diagrams E, F, concentric with the disc A and graduated, the one E having 365
divisions to show the days of the year, and the other F having 24 divisions to show
the hours of the day and subdivisions for minutes.
'The divisions of the hour circle F start as shewn at S at mid-day opposite the
division representing the 22nd day of March, and the division representing mid-night
at N on the one circle opposite the division of the other circle between 20th and 21st
of September.
Centred on the same axis as the disc A is a pointer G representing the mean sun
extending radially outwards towards these circles E, F.
When using the invention the first point C of Aries is set to the month and day,
which represents the sidereal time at mean noon at Greenwich on that day. The
sun pointer G is then placed at mid-day. By turning round the disc A which carries
with it the pointer it will be seen when any star on the diagram will cross the
meridian or due south in the Northern Hemisphere or north in the Southern
Hemisphere. If the ship is on either of these courses the star should be right ahead
at the time shown by the mean sun pointer. For the other points the Azimuth
cards, which shew the sidereal time abreast of every point, are needed.
Azimuth tables will be supplied with the instrument, and will be carried in the
frame H of the apparatus beyond the board D probably on the same ground plan as
the year and hour circles, or in the inside of the lid hinged to the case containing
the instrument. Four cards for each hemisphere,--either separately or in book
form, will be all that is required for that purpose, as each star crosses the meridian

page_text: about four minutes earlier every night or day sun time, the sidereal time being
constant in the same parallel of latitude.
It will be observed from the foregoing explanations that the instrument gives the
angle at the pole and the Azimuth cards the angle at the zenith. Fourteen stars
have been chosen which will pass the meridian south of the ship. The Azimuth
bearings of these stars have been computed to the nearest minute for every quarter
point of the compass from East North East round by south to West North West as far
as the stars selected are above the horizon when passing these points, the Azimuth
cards being prepared in a form similar to a railway time table.
The instrument may be used with the sun, moon or planets, as well as with the
stars, and rules for working with them will be provided.
The rules for using the indicating apparatus are as follows:-
Place the fixed pointer representing the first point of Aries to the day of the month;
turn the inovable pointer representing the mean sun to the letter S placed at the
south meridian or 22nd March. The instrument is then set for the day. Turn the
revolving dise till the first point of Aries pointer is at the sidereal time given on
the Azimuth card for the star chosen when on the meridian. The sun pointer
will then show the mean astronomical time, when the star will cross the. meridian.
See that the star chosen is in a straight line with the centre of revolution, which
represents the pole, and the letter S already referred to. If this is attended to no
mistake can be made in setting the instrument.
For any other course the disc is turned till the first point of Aries pointer is at the
sidereal time given on the Azimuth card for the course to be steered.
The sun
pointer will then show the mean astronomical time when the star chosen will cross
the centre line of the ship-bow if on a south course, or stern if on a north course-,
as all the stars in the first group on the Azimuth cards pass to the meridian south of
the ship.
Subjoined is a card of the star Aldebaran for the 55 parallel of latitude showing
the sidereal and mean times calculated for 1st January to show how the instrument
is worked

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 :-
Apparatus for indicating or correcting a ship's course at sea constructed substan-
tially as described and adapted to be used in conjunction with Azimuth tables such
as shewn and described
Dated this 22nd day of February 1899.
WALLACE FAIRWEATHER,
Of the Firm of Cruikshank & Fairweather,
Chartered Patent Agents,
62, Saint Vincent Street, Glasgow, Agent for the Applicant.