IMPROVEMENTS IN RUDDERS
Year: 1865

page_text: LETTERS PATENT to James Robert Napier, of Glasgow, Marine Engineer,
and William John Macquorn Rankine, of Glasgow University, Civil
PROVISIONAL SPECIFICATION left by the said James Robert Napier
and William John Macquorn Rankine at the Office of the Commissioners
of Patents, with their Petition, on the 29th December 1865.
We, JAMES ROBERT NAPIER, of Glasgow, Marine Engineer, and WILLIAM
JOHN MACQUORN RANKINE, of Glasgow University, Civil Engineer, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN RUDDERS," to
be as follows, that is to say :-
Our Invention consists in making the rudder of a vessel propelled by the
screw of such a shape that in the midship position of the rudder its surface
shall at each point of the forward edge stand in a direction tangential or
nearly tangential to the streams of water driven obliquely aft by the screw,
and that in the same position of the rudder its surface at each point of the
after edge shall stand in a fore-and-aft direction, or nearly so, the said surface
being fair and continuous between those edges. The object of the improve-
ment in the shape of the rudder is to increase the efficiency of the screw for
propelling, and of the rudder for steering. We prefer the balanced rudder,
but our Invention may be applied to the common rudder also, in which case
the rudder post is to be so shaped that its side surfaces shall form con-
tinuations of the side surfaces of the rudder in its midship position.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said James Robert Napier and William John Macquorn Rankine
in the Great Seal Patent Office on the 26th June 1866.
TO ALL TO WHOM THESE PRESENTS SHALL COME, we, JAMES
ROBERT NAPIER, of Glasgow, Marine Engineer, and WILLIAM JOHN
MACQUORN RANKINE, of Glasgow University, Civil Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-ninth day of December, in the year of our
Lord One thousand eight hundred and sixty-five, in the twenty-ninth year
of Her reign, did, for Herself, Her heirs and successors, give and grant unto
us, the said James Robert Napier and William John Macquorn Rankine,
Her special licence that we, the said James Robert Napier and William
John Macquorn Rankine, our executors, administrators, and assigns, or
such others as we, the said James Robert Napier and William John
Macquorn Rankine, our executors, administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times there-
after during the term therein expressed, should and lawfully might make,
use, exercise, and vend, within the United Kingdom of Great Britain and
Ireland, the Channel Islands, and Isle of Man, an Invention for "In-
PROVEMENTS IN RUDDERS," upon the condition (amongst others) that we,
the said James Robert Napier and William John Macquorn Rankine, our
executors or administrators, by an instrument in writing under our, or their,
or one of their hands and seals, should particularly describe and ascertain
the nature of the said Invention, and in what manner the same was to be
performed, and cause the same to be filed in the Great Seal Patent Office
within six calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that we, the said James Robert Napier and William
John Macquorn Rankine, do hereby declare the nature of our said Inven-
tion, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement in writing,
reference being had to the accompanying Drawings, that is to say:―
Our said Invention relates to the shape of the rudder of a vessel propelled
by the screw, and the object of the improvements is to increase the efficiency
of the screw for propelling and of the rudder for steering.
Our Invention consists in making the rudder of such a shape that when it
is in the midship position it has its side surfaces at each point of its forward
edge tangential or as nearly as practicable tangential to the streams of water

page_text: driven obliquely aft by the screw, and that when it is in the same position it
has its side surfaces at each point of the after edge standing in a fore-and-aft
direction, or as nearly so as practicable, the side surfaces being fair and con-
tinuous between the forward and after edges.
The said shape embodies two distinct improvements, one of which may be
used without the other. Thus the shaping of the side surfaces tangentially to
tbe streams of water driven obliquely aft may be employed alone, in which
case it will not be confined to the forward edge of the rudder. The effect of
this first portion of our improvements is twofold; on the one hand, to avoid
or diminish the abrupt checking of the transverse component of the motion of.
the water which is produced by the ordinary form of rudder with or without a
rudder post, and is a cause of shocks to the vessel and machinery, and of
waste of power, and on the other hand to improve the steering action of the
rudder by ensuring that as soon as it is put over to an appreciable angle all.
parts of the streams of water driven obliquely aft by the screw shall begin to
press on that side of the rudder towards which its after edge is put over,.
instead of some parts of those streams continuing to press on the contrary
side of the rudder until it is put over to an angle equal to the obliquity of the
motion of those parts, as is the case with the ordinary rudder.
The other portion of our improvements consisting, as herein-before indicated,
in making the side surfaces of the rudder fair and continuous from the forward
edge (shaped according to the first portion of our improvements) to the after
edge, shaped so as to stand fore and aft, or nearly so, causes portions of the
surfaces to gradually deflect the streams of water or portions of them from:
oblique directions into a direction due aft, or nearly so, whilst the reaction.
upon the rudder of the water whose motion is so deflected produces an.
additional forward thrust, co-operating with the thrust of the screw in over...
coming the resistance of the water to the motion of the vessel.
The kind of rudder to which we prefer to apply our Invention is that
commonly called the "balanced rudder," that is. to say, a rudder without any
rudder post or after stern post, and having part of its side surfaces afore and
part abaft the axis about which it turns. Nevertheless our Invention may
be applied to a rudder with a rudder post also, in which case we prefer to
shape the side surfaces of the rudder post so that they shall form continuations
of the side surfaces of the rudder in its midship position. .
'
And in order that our said Invention and the manner of performing the
same or carrying it into effect may be properly understood, we will now.
proceed to particularly describe a process. of designing a rudder so as to have.
the improved shape in which our Invention consists, and in doing this we

page_text: refer to a Sheet of explanatory. Drawings.which is hereunto appended, and on
which the same reference numerals and letters are used, to mark the same or
corresponding parts in all the. Figures in which they occur.
We first draw a side elevation of the proposed rudder as in Figure 1,
shewing its intended height and its breadth as projected on a vertical fore-
and-aft plane; also the position of its axis of motion; also the rudder stock
or rudder head of a diameter sufficient to give the requisite strength, which is
the same as in an ordinary rudder of the same dimensions. The rudder
represented in Figure 1 is a balanced rudder, but the same principle may be
applied to a rudder with a rudder post, the chief difference being in the
position of the axis of motion. Across the elevation we draw a straight line 5.
in the prolongation of the axis of the propeller shaft, and parallel to that
straight line we draw a series of other straight lines, such as 1, 2, 3, 4, 6, 7,,
8, 9, dividing the height of the rudder into convenient intervals, These
straight lines mark the positions of horizontal sections of the rudder, to be
afterwards drawn.
The second step is to construct a geometrical Diagram, such as that shown.
in Figure 2, in order to determine the proper theoretical angles of obliquity.
of the forward edge of the proposed rudder at the several lines of horizontal
section 1, 2, 3, &c. in Figure 1. The following is the construction of that s
Diagram:-Draw a straight line A, C, of any convenient length to represent
the speed of advance of the screw through a solid. In that line take C, B,.
to represent the real slip of the screw in the water, which real slip is computed
as follows: To the speed (if any) with which the particles of water imme-.
diately before being acted on by the screw are following in the wake of
the vessel, add the apparent slip of the screw, being the excess of its
speed of advance above the speed of the vessel. If the apparent slip of the.
screw is negative, it is to be subtracted instead of being added. In the case.
of a proposed vessel the data required for the calculation just described are to
be estimated from observations of the performances of similar vessels with s
similar screws. On C, B, as a diameter describe a semicircle; fiind the angles.
of obliquity of the after surfaces of the screw blades to a fore-and-aft line at
the different distances from the axis of the propeller shaft marked by the lines
of section 1, 2, 3, &c., in Figure 1, and through the point C draw a series.
of straight lines, making the same angles of obliquity with the line C, A, and a
cutting the semicircle in a series of points such as those marked D 1 and 9,
D2 and 8, D 3 and 7, D 4 and 6. From the series of points thus found
draw straight lines to the point A. Then the angles made by those lines
respectively with the line A, C, will be the theoretical angles of obliquity.

page_text: proper for the forward edge of the rudder at the points whose distances from
the axis of the propeller shaft are respectively the same with the distances.
taken in finding the angles of obliquity of the screw blades; in other words,..
let D denote any one of the points in the semicircle described on B, C,
corresponding to those parts of the screw blades whose obliquity to a fore-
and-aft line is D, C, A; then D, A, C, is the theoretical obliquity proper for
those parts of the forward edge of the rudder which are at the same distance
from the axis of the propeller shaft with the given parts of the screw blades.
In the case of an existing vessel and screw the theoretical angles of obliquity
for different parts of the forward edge of the rudder may be determined.
experimentally in the absence of any rudder or rudder post by immersing
suitable instruments resembling vanes in the current of water driven aft by
the screw, and observing the angles of obliquity at which they are placed by
the water; and the same angles may be used for similar vessels with similar
screws. The angles of obliquity shown in the Diagram ought to be adapted
to the ratio which the slip of the screw bears to its speed of advance in
moderate weather and at the ordinary speed. When the vessel is steaming
against a head wind or a head sea, or is driven at an excessive speed, the.
slip will be proportionally greater, and the angles shown by the Diagram will
no longer be precisely the theoretical angles corresponding to the increased
slip, but they will still be sufficient to enable the rudder to realise in a great
measure the advantages due to our Invention.
The Diagram of obliquities having-been completed as in Figure 2, the third,
step is to draw a series of horizontal sections of the proposed rudder .at
different distances from the axis of the propeller shaft. In drawing each of
those horizontal sections, we prefer to commence by drawing a skeleton line of,
a length representing the intended breadth of the rudder. If the rudder is to.
embody the first-part of our Invention only, that skeleton line.is simply. a
straight line, making the proper angle of obliquity to the proper side of another
straight line representing a fore-and-aft line. If the rudder is to embody the.
second part of our Invention as well as the first, the skeleton line of each
horizontal section is a fair continuous line of any convenient shape (such,.for
example; as a circular arc), having the tangent at its forward end. inclined at
the proper angle of obliquity in the proper direction, and the tangent at its
after end pointing right aft.. The proper direction for the obliquity in either
case is determined by considering towards which side the adjoining blades of
the screw drive the particles of water, Having drawn the skeleton line of. a'
horizontal section, we next mark in or near it .and at the intended distances
from its forward and after ends, a point to represent the intended axis of

page_text: motion of the rudder. We then lay off across the skeleton line at the axis of
the rudder, at the forward and after edges and at intermediate points, the
thicknesses required for strength according to the ordinary rules for pro-
portioning rudders, and we connect the thicknesses laid off by means of a pair
of fair continuous lines to represent the horizontal sections of the two side
surfaces of the rudder, taking care that those lines do not deviate from the
theoretical figure marked by the skeleton line more than is necessary, in order
to give sufficient strength.
Figure 8 shows by way of example a series of such horizontal sections for
the balanced rudder shewn in Figure 1, the skeleton line of each being
marked by dots, and the axis of the rudder by a cross and a small circle.
Horizontal section No. 5 is in the prolongation of the axis of the propeller
shaft, and its skeleton line is a straight fore-and-aft line. The other hori-
-zontal sections have curved skeleton lines, so as to embody both parts of our
Invention. Had those skeleton lines been straight so as to embody the first
part only of our Invention, all the sections would have been nearly similar to
No. 5, but at different angles of obliquity. Then if the rudder is made with
its side surfaces fair and continuous vertically, and so as to coincide with
the outline sections in Figure 3 at their respective heights as shown in
Figure 1, those surfaces will have the improved shape in which our Invention
consists.
In a rudder with a rudder post the axis is near the forward end of each of
the skeleton lines, and the rudder post is laid off on the horizontal section by
prolonging the skeleton line forward to the forward side of the rudder post,
and by laying off the siding of the rudder post across it. If required a
thwartship view of the rudder, such as that shown in Figure 4, may be
drawn by aid of the horizontal sections.
Figure 4 is a view from ahead of the forward edge of a balanced rudder
adapted to a righted handed screw. The outline of the screw is marked by
dotted lines, and the lines of horizontal section are numbered to correspond
with those in Figure 1 and with the sections in Figure 3.
The method of designing just described is that which we prefer, but it
may be varied in detail so long as the principles of our Invention are
adhered to.
And now having described the nature of our Invention, and the manner in
which the same is to be performed, we wish it to be understood that we
claim,―
First, the making of the rudder of a vessel propelled by the screw of such
a shape that in its midship position its side surfaces stand in a direction

page_text: tangential or nearly tangential to the streams of water driven obliquely aft by
the screw.
And, secondly, we claim the making of the rudder as respects its forward
edge of the shape mentioned in the first part of this claim, combined with the
making of it of such a shape that in its midship position its side surfaces at
cach point of the after edge stand in a fore-and-aft direction or nearly so,
whilst the intermediate parts of the surfaces are fair and continuous between
the forward and after edges, but we do not claim separately the making of the
rudder of the said shape as respects the after edge.
In witness whereof, we, the said James Robert Napier and William
John Macquorn Rankine, have hereunto set our bands and seals, this
Twenty-second day of June, in the year of our Lord One thousand
eight hundred and sixty-six.
JAMES R. NAPIER.
(L.S.)
W. J. MACQUORN RANKINE. (LS.)