AN INSTRUMENT TO BE USED CHIEFLY ON BOARD SHIP FOR APPROXIMATING IN CERTAIN CASES THE COURSE OF AN APPROACHING VESSEL EITHER IN THE DAY OR NIGHT, AND THE RELATIVE ANGLE OF BOTH SHIPS" COURSES, IN ORDER TO AVOID A COLLISION, TO BE CALLED PERRY'S ANTI- COLLISION DIAL
Year: 1858

page_text: LETTERS PATENT to Charles James Clowes Perry, of Williamstown, in
the Colony of Victoria, Member of the Legislative Assembly, for the
Invention of "AN INSTRUMENT TO BE USED CHIEFLY ON BOARD SHIP FOR
APPROXIMATING IN CERTAIN CASES THE COURSE OF AN APPROACHING VESSEL
EITHER IN THE DAY OR NIGHT, AND THE RELATIVE ANGLE OF BOTH SHIPS"
COURSES, IN ORDER TO AVOID A COLLISION, TO BE CALLED PERRY'S ANTI-
COLLISION DIAL."
Sealed the 12th May 1859, and dated the 16th November 1858.
COMPLETE SPECIFICATION filed by the said Charles James Clowes Perry
at the Office of the Commissioners of Patents, with his Petition and
Declaration, on the 16th November 1858, pursuant to the 9th Section
of the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, CHARLES
JAMES CLOWES PERRY, of Williamstown, in the Colony of Victoria, Member of
the Legislative Assembly, do hereby declare that the nature of the Invention
for "AN INSTRUMENT TO BE USED CHIEFLY ON BOARD SHIP, FOR APPROXIMATING IN
CERTAIN CASES THE COURSE OF AN APPROACHING VESSEL EITHER IN THE DAY OR
NIGHT, AND THE RELATIVE ANGLE OF BOTH SHIPS' COURSES, IN ORDER TO AVOID A
COLLISION, TO BE CALLED PERRY'S ANTI-COLLISION DIAL," to be particularly
described and ascertained in and by the following statement thereof, that
is to say :-
The great desideratum attending many cases of collision, and of vessels

page_text: passing and crossing very near each other in the night time, appears to be an
adequate knowledge of the direction in which each other ship is steering, or
else what is almost the same thing, the particular tack on which the approach-
ing ship is sailing. Through this difficulty much anxiety is experienced, and
many fatal mistakes made; for whilst the masters of the approaching ships in
many cases feel uncertain whether the vessels will clear each other, they also
experience great embarrassment in altering the helm lest they should thereby
incur the collision they are attempting to avoid. It is conceived, then, and
hoped by the Inventor, that a general use of the anti-collision dial will supply
this desideratum by affording a timely knowledge to the captains of both ships'
courses, and the relative angle at which they approach each other. This
intelligence is calculated greatly to mitigate the danger of approaching closely
in the night, for it not only enables the captains to act with deliberation and
precision in altering the helm of their respective vessels should circumstances
require it, but it also enables them to act in harmony with each other. The
proper means of avoiding each other's ships in the event of approaching too
near having become obvious to the captains beforehand. The instrument
consists of a flat piece of metal or any other suitable material, upon which to
the extent of three-fourths of a circle, a corresponding portion of the points,
half points, quarter points, and eighths of points of the compass are repre-
sented by lines of perforations, in the manner shewn by the accompanying
Drawing. The instrument, moreover, is of circular form, and about sixteen
inches diameter, the centre being marked by a perforation. It has at about
an inch from its circumference a thick or double circular line swept around at
an equal distance from the centre of the instrument, and called the "inner
marginal line," marked A in the Drawing. This line forms the outer limit to
the perforated points and their divisions, and from it proceeding inward they
all converge towards the centre, but do not all extend to the same distance.
The distance between the centre and the inner marginal line represents seven
miles, and is divided into seven equal parts by a series of circular lines about
an inch apart, and called mile circles, marked B in the Drawing. These
circles crossing the points and their divisions, serve to measure them into miles
along their lengths, and to denote at the points of intersection miles of distance
from the centre, whilst the intervening perforations indicate tenths of a mile on
one part of the dial, that is, from the second mile circle inward towards the centre,
and eighths of a mile on all the other part, viz., from the second mile circle
outwards towards the "inner marginal line." The mile circles are numbered
from the centre outwards, and are marked accordingly on the cardinal points
and their principal intermediate ones. The extension of the points and their

page_text: divisions from the "inner marginal line" towards the centre is as follows:-
The points reach in to about a quarter of an inch from the centre, the half
points to the first mile circle, the quarter points to the second mile circle, and
the eighths to the third mile circle. The perforations along the points and
their divisions serve not only to subdivide them into fractions of miles between
the mile circles and between the first mile circle and the centre, but also to
mark off positions by having pins inserted in them. The points, half points,
and quarter points are indicated by lines, as well as by perforations, but they
are visible only between the holes. They are also drawn of different thick-
nesses to distinguish more readily the cardinals from the other points, and the
points from the halves and quarters. As already stated, the distances from the
centre are measured along the points and their divisions in miles by the mile
circles, the first mile circle denoting one mile from the centre, the second mile
circle two miles from the centre, and so on, and the intermediate perforations
tenths of a mile between the second mile circle and the centre, and eighths of a
mile between that circle and the inner marginal line. Any given distance from
the centre can therefore be readily marked off with a small pin upon any given
point,. half point, quarter point, or eighth falling within the scope of such
distance. Outside the "inner marginal line" three other circular lines are
drawn about one-third of an inch apart; the two innermost of these surround
the entire circle of the dial, and the space they include is divided by perfora-
tions into sixty equal parts, and numbered at every five to represent the
minute circle of a watch. Around the spaces inside and outside of the minute
circle the names of the points are written in two opposite series. The middle
point of the whole number upon the dial is distinguished by a fleur-de-lis at
its extremity, and is to be considered as the north point when the inner series
of names is adopted, and as the south point when the outer series is adopted.
For it is intended that the portion of the hemisphere included between the
points marked N.E. and N.W. in the inner series shall be used instead of the
corresponding portion in the opposite hemisphere on which the points are not
inscribed, so that whenever the observing ship's course or the bearing of a light
or other object falls between the S.E. and S. W. points of the ship's compass,
the same is to be represented on the dial by adopting the outer series of names,
but whenever that portion of the dial which has not the points inscribed on it
does not interfere with the working of the instrument the inner series of names
is to be used. Upon that quadrant of the circle not occupied with points is
legibly written a table of distance which shews to the tenth of a mile quantities
of distance agreeing with different velocities and different intervals of time.
The first vertical column under the head of "knots" represents hourly speed,

page_text: and embraces rates of from three to fifteen minutes. The upper horizontal
column under the head of "minutes of time" represents different intervals
of time from two minutes to fifteen minutes; this table is exhibited in
the Drawing. In addition to the table on this portion of the instrument, there
is a circular line of perforations about an inch from the centre, and to every
alternate perforation a line drawn from the centre indicating an extension of
that point from the opposite hemisphere directly opposite the perforation.
One of these holes is to be used in a case of the observing ship making little
or no progress during the measured interval of time. A pin is to be placed
in whichever hole is in a line with the ship's course, to serve in connexion
with another placed in the centre to receive the model representing the
course of that vessel. The foregoing description, as respects the size of the
instrument, applies to one constructed upon a scale of one inch to a mile; this
I conceive to be the most portable size for practical purposes, but it may be
made upon a larger scale and a larger range than seven miles given between
the centre and inner marginal line whenever a proportional increase of size is
not objectionable. The auxiliaries to this instrument consist of, first, ten small
pins of metal about an inch long, and one-twelfth of an inch diameter along
their lengths, and slightly pointed at one end. These fit the perforations on
the dial, which are all of one size, and about one quarter of an inch deep.
Six of the pins will in most cases be sufficient to use at one time. Six small flat
models in the form of the longitudinal deck section of a ship, about three and
a half inches long, having a hole in them near the sharp end, and a slit along
the middle commencing a quarter of an inch from the hole, and extending to
within half an inch of the opposite or square end of the model. The diameter
of the hole and the breadth of the slit are just large enough to allow the model
to slide easily down over two of the metal pins when they are inserted in the
perforations of the dial. The models may be made of bone or any other
suitable material, and on the right side of each is a small space colored
green, and on the left side a similar space colored red, to represent the
colored lights carried by steamers, and so placed and screened as to
show on the same angle laterally as that prescribed for steam vessels.
Two of the models project from their sharp ends a narrow scale of
about four inches long and graduated to miles and quarters, on the same scale
as on the dial, this is to shew distance in miles and fractions from the pin
which passes through the circular hole. These two models are to be used
before a board of enquiry only, and of the other four, two only in most cases
will need to be used, as one for each ship is sufficient. For the form of the
models, see Figures C and D in the accompanying Drawing.
Thirdly, a

page_text: parallel ruler with double slide, having two graduated edges to represent
distance in miles and quarters constructed on the same scale as the miles on
the dial. An angular piece is cut out of one end of each slide of this ruler to
prevent it in certain cases from coming in contact with the pin, which marks
the first position of the approaching ship, as hereafter described. In using
the ruler, it will be convenient to observe that the cut ends should be to the
right hand when the approaching vessel is to the right or starboard of the
ship's course, and to the left hand when it is to the left or port of such course.
For a figure of the ruler, see Drawing. Fourth, a small scale of about three
inches in length, which will be required occasionally for correcting the first
estimated distance with, it has three miles of distance marked on it graduated
to tenths. I would have it understood, that with the exception of the models,
I do not claim novelty for any of the auxiliaries just described, nor are
they to be considered as any part of the Invention for which I have petitioned
for Letters Patent. The data employed in approximating the course of an
approaching ship in the night time, consist of two bearings of the vessel's light,
the estimated distance at each bearing and the measured interval of time
between them. In every case, therefore, where a ship, sailing or steaming in
the night time, sights the signal light of an approaching vessel, under circum-
stances which admit of sufficient time to use the instrument in the manner
hereafter described, the course pursued by the approaching vessel during
that interval of time may be approximated. The process of using the instru-
ment may be performed in three minutes, and in considerably less time than
that by a person familiar with its use. Moreover, about one-third of the
process takes place immediately after the first bearing is taken, and during the
necessary interval of time between the first and second bearings. When an
expeditious use of the instrument is required, on account of the great speed at
which both vessels are advancing towards each other, a proportionably short
interval of time between the bearings will suffice, and if the minimum interval
of two minutes, as shewn in the table be adopted, it may be considered that the
course of an approaching vessel can be approximated in about four minutes after
taking the first bearing of the light. Now we find, that two swift steam ships
advancing towards each other in a direct line, at a speed of twenty-four miles
an hour, that is twelve miles an hour each, would occupy twelve and a half
minutes to meet from a distance of five miles, that being the distance at which
the present Admiralty regulations enjoin their mast-head light to be visible in
clear weather, and at which distance it may therefore be supposed the steamers
would sight each other's lights; but at a right angle those vessels, at the same
speed, would require seventeen and a half minutes to meet from the same

page_text: distance. Then in respect to sailing vessels whose speed, through the varying
strength of the wind, is generally inferior to that of steamers, but whose light is
also not to be seen at so great a distance, it may fairly be assumed that upon
an average they afford at least as long an interval of time between sighting the
light, and crossing each other's track, as do steam ships. It may, therefore, be
presumed that the use of the instrument will be generally applicable to all
vessels exhibiting a light visible at a maximum distance of not less than three
miles. The manner of using the instrument in the night time is as follows:-
Immediately a vessel's light is sighted, the officer in charge of the ship observes
its bearing by the ship's compass, notes the time by the minute hand of a watch
(disregarding hours and seconds), and estimates the distance the light is
from his ship. He then marks off on the dial, first, the number of
minutes shewn by the watch by inserting a pin in the perforation on the
"minute circle" corresponding thereto; secondly, the bearing and distance
by placing another pin at a corresponding distance from the centre on
the point, half point, quarter point, or eighth, as the case may be, repre-
senting that on which the light was seen to bear by the ship's compass. He
has now the approximated first position of the light, and also the first position
of his own ship for the centre of the dial is always assumed to be the first
position of the observing vessel, but it is not marked off with a pin until the
second positions are marked, otherwise it would impede the use of the parallel
ruler. After the lapse of an interval of time from the first bearing, which
may range from two minutes to fifteen, according to the rapidity or otherwise
with which the light seems to approach, the officer again takes the bearing of
the light, notes the minutes by the watch, and estimates the distance off. He
then marks the minutes off on the minute circle as before, and proceeds as
follows: With the number of minutes shewn between the two pins on the
minute circle he enters the upper column of the table of distance marked
"minutes of time," and looking down the vertical column agreeing thereto,
takes out the quantity of distance standing in a line with that number in the
"knots" column, which represents or nearest represents the hourly speed of
his ship, and marks it off on the point or half point or the nearest point thereto,
representing that on which his ship is steering. This pin denotes the second
position of the observing ship, he then places the parallel ruler across the
centre of the compass with the cut end near the pin, marking the first position
of the light and the edge of it along the point, half point, or quarter point
representing the second bearing of the light, then sliding forward the graduated
edge to touch the last inserted pin, he counts along the scale from that pin a
number of divisions equal to the second estimated distance, and fixes another

page_text: pin there in the nearest hole; this marks the approximated second position of
the light. The officer now by placing a pin in the centre has approximately
the relative positions of both vessels when the first and second bearings were
taken, and the process is completed by sliding down a model (like that marked
C in the Drawing) over each pair of pins, letting the pins marking the second
positions pass through the circular holes, and the other ones through the slits.
The positions of the models on the dial will now shew, first, the approximated
course or angle with the meridian pursued by the approaching vessel during
the interval of time between the two bearings. The compass point agreeing
to that course is shewn by referring the line of direction of the two pins,
marking the positions of the light to the centre of the dial with the parallel
ruler; secondly, the relative angle of both ships' courses as represented by the
longitudinal inclination of the two models towards each other. In addition to
these two results (the ascertaining of which may be considered as the stated
objects of the Invention), the positions of the models will also shew which of
the two colored lights should be visible or become visible if it is the mast-head
light of a steam ship which has been observed. Moreover, by observing the
following general rule, the instrument will always indicate whether by con-
tinuing their respective courses and rates of speed, the approaching vessel will
pass ahead or astern of the other ship, or whether there is danger of their
coming into collision. Whenever the pin marking the second position of the
light is to the left hand (as viewed from the second position of the observing
vessel) of a parallel with the line of the two first positions, it shews that the
approaching vessel will pass ahead or across the bows of the other ship at a
greater or lesser distance, if the light was first observed on the starboard side
or bow, and that she will pass away clear on the port side at a greater
or lesser distance, or else "drop" or cross the stern if the light was first
observed on the port side or bow, and vice versa, whenever that pin is to
the right of such parallel line. Again, when the second positions form a line
parallel with the line of the first positions, then the instrument indicates that
the vessels will pass so near to each other as to endanger a collision, and it
behoves the officer observing this to be on the alert, either to slacken
his speed in good time to allow the other. vessel to pass ahead or be prepared
to alter his course with a port helm, or to do both according to the circum-
stances of the case and his own discretion. Now, the relation of the line
of the second positions to the line of the first positions can be at once
determined simply by reverting to the two bearings taken by the ship's
compass without any reference whatever to the dial. For as a parallel line
may be taken to mean a line on the same bearing of the compass, it

page_text: follows that when the line of the second positions is parallel with that of
the first ones, the first and second bearings must have been precisely on the
same point of the compass, and when that line is to the left or right of such
parallel, it implies that the second bearing was to the left or right of the first
bearing, as both were taken by the ship's compass. It may therefore be said,
in respect to the results under this head, that the two bearings previously
indicate what the dial also indicates and mathematically demonstrates. Any
probable amount of error in estimating either the first or second distance does
not necessarily affect the main result, viz., the angle with either the meridian
or the other ship's course on which the approaching vessel is steering.
Neither does a considerable error in both distances affect it when that error is
of the same character and co-extensive in each, viz., when both the estimated
distances are to the same extent greater or smaller than the true distances;
for whether the estimated distances be true or equally in excess of or less than
the true ones, the instrument will alike indicate the true course of the ship.
It may be assumed, however, that some degree of error will always attend the
estimate of both distances under the present system of ship's lights, but it is
only by an inequality in those errors that the result is more or less affected, or
when they happen to be of opposite characters, as when the first estimate is
too great, and the second one too small, and vice versa. This last kind of
error is not likely to happen with an observer of any experience keeping a
good look-out, and having regard to the character of the observed light, and
the distance at which it may be presumed first to become visible from. Any
error, however, of a character to materially affect the result will be generally,
if not always, indicated to the mind of the officer by the improbable amount of
distance shewn between the two pins marking the first and second positions of
the approaching vessel, and representing the distance run by that vessel during
the measured interval of time; for in addition to what has just been stated
about the light, as being a guide to the officer, it may be added that the state
of the wind, and the rapidity or otherwise with which the light approaches,
will in most cases enable him to judge whether the vessel is a steamer or a
sailing ship, and to estimate accordingly the speed of that vessel at least
within three or four knots per hour. The connection, therefore, which in all
such cases is to be made, and indeed whenever it is suspected that the
estimated distances are in no degree reliable, is very simply effected. The
observer has only to shift the pin, marking the first position of the light to
such a distance from the other pin as will shew what he deems to be the
probable run of the approaching vessel during the measured interval of time,
observing in doing so to keep it on the same point of the compass. In

page_text: making this correction, the use of the table and the small scale will be con-
venient. It is proper to remark, that in proportion to the accuracy of the
distance indicated to be run by the approaching ship will always be the
accuracy of the approximated course, so that in any case when the speed of
that vessel is known, and the correction made accordingly in the manner
before directed, the true course of that ship will be shewn; the observer,
therefore, has always the option of neutralizing suspected errors in the esti-
mated distances, by simply adapting the first distance to his estimate of the
approaching ship's run, in the manner before described.
It may not be out of place here to observe that the lights at present carried
by steam ships do not indicate their courses within many points, inasmuch as.
each light shews round from right a-head to an angle of ten points; whereas
if an arrangement of those lights were adopted, by which successive distances
would be indicated, the use of the dial in the night time would exemplify the
courses of those vessels with more precision than they could be judged of in
the daytime from the same distances. If two or more vessels' lights should
be sighted at the same time, the process of approximating their several courses
may be simplified whenever practicable by taking their first bearings together,
allowing one and the same interval of time for all, and then taking their
second bearings together, then the pin which marks off the quantity taken
from the table of distance will denote the second position of the observing
vessel, in relation to the second positions of all the other ships, whilst the.
centre of the dial, which is always the observing vessel's first position, will
likewise correspond to their first positions.
The process for indicating the first and second positions of each approaching
ship is of course similar to that which has been described for one. The
instrument will also be found useful to indicate the distance off shore at which
a vessel sails along a coast, passes a cape or any other fixed object, or a light-
house in the night time by means of two bearings, and the estimated or
measured distance run by the ship in the meantime. For this or any other
purpose, the one mile divisions of the points may be considered to represent
either two, four, or eight miles. When the instrument is used in the daytime
precisely the same process is to be observed as directed for the night, only
instead of taking the bearings of a light, the bearings of the vessel are to be
observed. The dial will further be found useful to elucidate cases of collision
before a board of enquiry. The pins on the points and centre represent in
pairs the first and second positions of each vessel, also the direction or course
which they are respectively steering, whilst the distances between each pair
indicate the distance run by each vessel during the measured interval of time.

page_text: The models are only applied to illustrate more familiarly the courses of the
vessel and their relative angle.
Having thus described the nature of the Invention, and the manner of
performing the same, I would have it understood that I do not confine myself
to the precise details so long as the character of the Invention be retained;
but what I claim as the Invention for which I have petitioned for Letters
Patent is, the construction of the instrument herein described, to be used chiefly
on board ship, in connexion with a compass, for the purpose of approximating,
in such cases as are herein specified, the course of an approaching vessel, and
the relative angle of that course with the one steered by the observing
vessel in order to avoid a collision.
In witness whereof, I, the said Charles James Clowes Perry, have here-
unto set my hand and seal, this Fifteenth day of September, in the year
of our Lord One thousand eight hundred and fifty-eight.
Signed, sealed, and delivered in the
presence of
A. FORD,
No. 76, Chancery Lane,
Melbourne.
C. J. PERRY. (L.S.)