IMPROVEMENTS IN PROPELLING VESSELS
Year: 1853

page_text: LETTERS PATENT to Charles Augustus Holm, of 21, Cecil Street,
Strand, in the County of Middlesex, Civil Engineer, for the
Invention of "IMPROVEMENTS IN PROPELLING VESSELS."
PROVISIONAL SPECIFICATION left by the said Charles Augustus
Holm at the Office of the Commissioners of Patents, with his
Petition, on the 24th March 1853.
I, CHARLES AUGUSTUS HOLM, of 21, Cecil Street, Strand, in the
County of Middlesex, Civil Engineer, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN PROPELLING VESSELS" to be as
follows:-
The object of this improvement is to supply a remedy against the
long and well-known defects of the common screw propeller in its
application to the propelling of vessels; these defects are the difficulties
experienced by engineers in obtaining sufficient resistance in the fluid
on the surface of the common propeller within the ordinary limits of the
draft of water of vessels to be propelled, and particularly so in the
application of the propeller to vessels having to contend against head
wind and sea, and also to what is called full power vessels; the screw

page_text: propeller, it may be said, has at the present stage of the Invention only
been successfully applied as an auxiliary to sailing vessels, and had
either failed or been rejected for high speeds, such as are required for
the mail service; but independent of the inadequate resistance of the
common propeller, it has another great defect which causes it to waste
under the most favourable applications and circumstances at sea a very
large part of the motive power applied to work it. I have discovered
that this great waste of power is caused by centrifugal discharge of a
great portion of the fluid called "slip" at the circumference of the
propeller in a line perpendicular to its axis. Now my Invention is
such that by a peculiar construction of the surface of the propelling in-
strument I am enabled to direct and discharge the fluid called "slip" in
a line parallel to the axis of the instrument, or nearly so, and by means of
which the motive power consumed in generating the centrifugal slip
becomes available for the purpose of propelling the vessel; and further,
in order to satisfy myself of the correctness of the principle, and to
ascertain the dynamic value of the improvements, I have made a series
of experiments, and by the result thereof I am enabled to give the
following description of the main points.
My improved propeller may, as the ordinary propeller, be made of
more than two blades, but I will only describe one of these blades, in
order that the different form of the different parts or portions of each
blade may be understood separately from each other. I will therefore
divide each blade into five distinct parts, each being of a form geometri-
cally different from the other, only one of these parts having the form
of what is known as the ordinary screw propeller blade, and which
part I will call No. 1, and suppose it to be th part of the pitch
or projection of the propelling surface. Now to the circumference of
this part (No. 1,) I apply part No. 2, composed of a curved screw
flange of the same pitch as part No. 1, and I call this screw flange the
centrifugal curve, which is generated by a quarter of a circle, the
radius of which is d part of the radius of part No. 1; this quarter
of a circle, when united with the radius of the part No. 1, forms
the generatrix, by which the helicoidal surface of the blade is com-
posed; and the part Nos. 1, and 2, when so united, may either be of an

page_text: uniform pitch or have an increasing pitch, or have an expanding pitch,
that is to say, a reduced pitch near the shaft equivalent to the amount of
slip produced by the circumferential part. Now whatever may be the
construction of these parts I further apply to them a lateral curve,
which is also to be a portion of a circle, and I call this part No. 3;
this lateral curve united by the centrifugal curve No. 2, would form, as
it were, a curved flange on two of the edges of part No. 1,-that is to say,
round the circumference and radial on the sternmost edge on the screw
part No. 1; but in order that these two curves (part Nos. 2, and 3,)
shall not represent a sharp corner at the point where they, if extended,
would meet, I unite them by a curve, which is a portion of a hollow
sphere of the same radius as the centrifugal curve, and I call this
sphere part No. 4; these several curves (parts No. 2, 3, and 4,) should,
when united with part No. 1, form a perfectly smooth surface, and the
rise of the curves should be such as to direct and deliver the propelling
current in a line parallel to the axis of the instrument, or nearly so,
through the lateral or radial curve (part No. 3,) may be gradually
diminished towards the centre of the shaft where the instrument has
little or no propelling power; the increased resistance of the blade by
these lateral curves (Nos. 3, and 4.) would readily account for the
increased action that must take place when the instrument revolves,
inasmuch as these curves prevent to a great extent the escape of the
fluid through the instrument, or rather between two of the blades; and
thus a portion of the fluid becomes lodged in the cavity formed on or
in each of the blades by these different curves (Nos. 2, 3, & 4), and
which causes such portion of the fluid to revolve with the instrument,
when the centrifugal force or momentum of the mass of fluid so
revolving would operate and give out its power partly on the lateral
curves (Nos. 3, & 4), but more especially on the centrifugal curve
(No. 2), and the centrifugal power of the current would by that means
he delivered in a line parallel to the axis of the instrument, and in
opposite direction to the axial motion of the propeller.
The description now given would make a very effective instrument
for propelling the vessel ahead, but would have no effect in propelling
the vessel astern, or as it is termed backing the vessel; I therefore

page_text: apply to the back of the instrument a backing screw curve similar in
pitch, diameter, and radius of generatrix for the curve as the centrifugal
curve (No. 2), but without any lateral curves. By the application of
this backing curve the instrument becomes further improved, inasmuch
as this curve prevents the centrifugal curve from drawing up a portion
of the fluid from the contral part by the adhesion of the particles of
fluid to its surface when the instrument revolves, which, to a certain
extent, diminishes the effect; the screw blade (part No. 1), may also, for
the purpose of backing, be extended in a straight line, or only be
slightly curved, but I believe if it be a quarter of a circle, as the
centrifugal curve, it would be most effective for the purpose.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Charles Augustus Holm in the Great Seal Patent
Office, on the 24th September 1853.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I,
CHARLES AUGUSTUS IIоLM, Civil Engineer, of 21, Cecil Street, Strand,
in the County of Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by IIer
Letters Patent, bearing date the Twenty-fourth day of March, in the
year of our Lord One thousand eight hundred and fifty-three, in the
sixteenth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Charles Augustus Holm, Her special
licence that I, the said Charles Augustus Holm, my executors, nd-
ministrators, and assigns, or such others as I, the said Charles
Augustus Holm, my executors, administrators, and assigns, should at
any time agree with, and no others, from time to time and at all times
thereafter 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 "IMPROVEMENTS IN PROPELLING VESSELS," upon the con-
dition (amongst others) that I, the said Charles Augustus Holm,
by an instrument in writing under any hand and seal, should par-

page_text: ticularly 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 I, the said Charles Augustus Holm, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement thereof (that is to say):
The object of this improvement is to supply a remedy against the
long and well-known defects of the common screw propeller in its appli-
cation to the propelling of vessels; these defects are the difficulties
experienced by engineers in obtaining sufficient resistance in the fluid
on the surface of the common propeller within the ordinary limits of
the draft of water of vessels to be propelled, and particularly so in the
application of the propeller to vessels having to contend against head
winds and sea, and also to what is called full power vessels; the screw
propeller has, it may be said, in the present stage of the Invention, only
been successfully applied as an auxiliary to sailing vessels, and has
either failed or been rejected for high speeds, such as are required for
the mail service on long voyages; but independent of the inadequate
resistance of the common propeller, it has another great defect which
causes it to waste under the most favorable applications and circumi-
stances at sea a very large part of the motive power applied to work it.
I have discovered that this great waste of power is caused by centrifugal
discharge of a great portion of the fluid "called slip," at the circum-
ference of the propeller in a line perpendicular to its axis. Now my
Invention is such that by a peculiar construction of the surface of the
propelling instrument I am enabled to direct and discharge the fluid
"called slip" in a line parallel to the axis of the instrument, or nearly
so, and by means of which the power consumed in generating the
centrifugal slip becomes available for the purpose of propelling the
vessel.
The character of my Invention may be said to be an improvement
on the ordinary screw propeller, whatever may have been the mode
adapted to determine the pitch uniform, or increasing either in the

page_text: direction of the axis or in the direction of the radius; and my said
improvements consist in the application of curved flanges forming part
of the propelling blade, these curved flanges are placed on two sides of
cach blade; that is to say, one of them is placed at the circumference,
and the other is placed at the sternmost edge of the blade, in the
direction of the radius; but in order that these two curved flanges
shall not form a sharp corner at the point where, if extended, they
should meet, I unite them by a curve, which is a portion of a hollow
sphere or any other curved cavity, which would efficiently unite the two
curved flanges; so as to form a spoon-shaped cavity in the sternmost
corner of the propelling blade; and thus by the combination of these
curved flanges, I am enabled to direct or discharge the propelling
current in a line parallel to the axis of the instrument, or nearly so.
In addition to the above mentioned flanges, I further apply to the
back of each blade another curved flange, but only at the circumference,
and in an opposite direction to the above-mentioned flange, by means
of which the instrument becomes useful for the purpose of backing the
vessel.
By the increased resistance in the fluid more motive power may
effectively be applied to the working of my propeller, hence greater
speed may be obtained than that realised either by screws or paddle
wheel; and with an equal expenditure of motive power the new
propeller will give greater speed to the vessel, with a smaller number of
revolutions of the propeller shaft, and would further admit of propelling
vessels with smaller draught of water than hitherto, and would be
also applicable to vessels navigating on rivers and canals, from the
circumstance of the propelling current being delivered in a line parallel
to the axis instead of perpendicularly, no risk would be incurred in
destroying the banks of the canals.
My improved propeller may, as the ordinary propeller, be made of
more than two blades, but I will only describe one of those blades, in
order that the different form of the different parts or portion of each
blade may be more clearly understood separately from each other. I
will therefore divide cach blade into five distinct parts, each being of a
form geometrically different from the other, and only one of theso

page_text: Figure 1, is a front view of a propelling instrument with two blades.
Figure 2, a section through the line A-B, taken at right angles to
the surface.
Figure 3, a side clevation or projection of the curves.
Figure 4, a section of the blade taken through the line C, D.
Figure 5, an end view of the blade; the same letters have reference
to similar parts in all the figures.
In Figures 1 and 3, I have drawn the lines C, D, and E F, in order
to be able to explain as above mentioned, separately from each other,
the different form of the different portions of which the propelling
instrument is composed; the part G, is a portion of a common screw
propeller, to which I have added a screw curve H, which I call the
centrifugal curve; this centrifugal curve is generated by a quarter of a
circle, the radius of which is one fifth part of the radius of the exterior
diameter of the propeller; this quarter of a circle, when united with the
radius of the part G, forms the generatrix, by which the helicoidal
surface of the instrument is composed; and the part G, and H, when
united, may either be of an uniform pitch, or have an increasing pitch, or
have an expanding pitch, that is to say, a reduced pitch near the shaft
equivalent to the amount of slip produced by the circumferential part.
Now whatever may be the construction of these parts I further add
to them a lateral curve K, which are also portions of a circle; these
lateral curves united by the centrifugal curve H, would form a curved
flange round the circumference, and at the same time on the sternmost
edge of the blade G; but in order that these two curves shall not
represent a sharp corner at the point where, if extended, they would
meet, I unite them by a third curve L, which is a portion of a hollow
sphere of the same radius as the centrifugal curve; these three curves
should, when united with the screw blade G, form a perfectly smooth
surface, and the rise of the curves should be such as to deliver the pro-
pelling current in a line parallel to the axis of the instrument, or nearly

page_text: so, though the lateral curves K, may be gradually diminished towards
the centre of the shaft where the instrument has little or no propelling
power; this diminution of the lateral curves K, is shown in Figures 3
and 4; the lines M, M, N, N', and 0, 0', in Figure 1, aro shewn by
corresponding lines and letters in Figure 4, representing the variation of
the angles combined with the lateral curve.
The increased action that takes place on the instrument when it re-
volves would easily be understood by considering the increased resis-
tance offered by the lateral curvo to the escape of the fluid through or
between two of such instruments, and by means of this resistance a
portion of the fluid lodged in the cavity formed on or in the instrument
by the different curves causes such portion of the fluid to revolve with
the instrument, when the centrifugal force or momentum of the mass of
fluid so revolving would operate and give out its power partly on the
lateral curves, but more especially on the centrifugal curve, and the
centrifugal power of the current would by that means be delivered in a
line parallel to the axis of the instrument, and in an opposite direction
to the axial motion of the propeller, as shown in section at Figure 2.
The description now given would make a very effective instrument
for propelling the vessel forward, but would have little or no effect in
propelling the vessel astern, or, as it is termed, backing. I have, there-
fore, applied to the back of the instrument a backing screw curve P,
shewn in Figures 2, 3, and 5, of the same pitch and radius of curve as
the centrifugal curve II. The screw blade G, may also, for the purpose
of backing, be extended in a straight line, or only be slightly curved; but
I believe the form shewn in the drawing would be most effective for the
purpose. The dotted lines in Figure 4, represent the extent that the
centrifugal curve and backing curve would assume when united to the
instrument, and this is further shewn in the exterior view of Figure 5.
Figure 6, is a diagram showing the triangle of the developement of
one blade, if extended to the circumference, and of an uniform pitch
combined with the lateral curve K, in such a manner that the
hypothenuse of the triangle on the one part, and the perpendicular
on the other, shall at the same time form tangents to the lateral
curve.

page_text: Figure 7, is a diagram showing the triangle of the developement of
one blade, if extended to the circumference, and of an increasing pitch
combined with the lateral curve K, of which the perpendicular of the
triangle on the one part, and the line representing the increasing pitch,
or, as is termed, curved directrix, on the other, forms at the same
time tangents to the lateral curve; this curved directrix should, in
order to be most effective, be a parabola; that is to say, it should
accelerate the particles of fluid to be put in motion in the same manner
as the acceleration of a falling body; thus, if the triangle A B C,
represent the developement of the circumference of one blade of which
A B, is the pitch corresponding to the portion of the pitch employed, I
set off from the point A, a portion of A B, equivalent to the amount
of slip, say rd of A B, then A D, will represent the slip, and
the triangle B, C, D, the propelling wedge at the circumference of the
instrument. Now if the base C, B, of the triangle be divided in four
equal parts the perpendicular lines E, F, and G, I divide A D, in a
number of divisions corresponding to the square of the number of
divisions of the base of the triangle; that is, the square of four
divisions equal to sixteen divisions of the line A ; and from the
points where the hypothenuse D, C, intersects the lines E, F, and G, I
set off for the rising curve on the line E, th part of A D; on F,
th of A D; and on G, th parts of A D; and I draw through
those points horizontal lines, and in the intersections of those lines with
the lines E, F, and G, I draw the curve which forms a directrix that
will accelerate the particles of fluid to be put in motion in the ratio
of the square of the number of divisions on the base of the triangle
respectively, and the directrix is further, completed with or by the
lateral curve K, as shown and described; these two diagrams would be
useful in constructing templates or guide plates for the moulding or
making of patterns for the instrument, and similar templates may also
be constructed for any other part of the radius on the principle de-
scribed. I should remark, that though I prefer the curved directrix
for the construction of my propeller as being the best means of pre-
venting vibration of the stern of the vessel, I do not always apply it
to the whole extent of the surface, as shewn in the diagram, but only

page_text: partly to the entering edge of the blade; thus, if the pitch be more
than to 1 times the diameter of the propeller. I only apply the
parabolic directrix to the extent of rd or of the surface from the
entering edge of the blade of the parts G, and II, and then the pitch
would afterwards continue to be uniform until it reaches the point
where it is to be united with the lateral curve; and this increase would
be suflicient, as the object of the diminution of the pitch at the entering
edge is only to prevent such entering edge of the blade to strike the
water too suddenly, by which it would rebound from the instrument.
I should further observe, that the pitch should, in order to ha most
effective, not to be more than double the diameter of the propeller.
When the propeller is made with more than two blades, the total
area of the projection of such blades should not exceed one half the
area of the entire disc; and in some cases, when it be desirable to mul-
tiply the number of blades, I unite them by means of portions of a
cylinder, which portions of a cylinder may have the same breadth, or
nearly so, as the breadth in the line of the axis of the propelling blades.
Figures 8, and 9, show this modification of my propeller. R, R, R,
show portions of a cylinder united to the centrifugal and backing
curves; the other letters in this figures referring to similar parts of
the propeller as those described in the former figures. This modifica-
tion of my propeller would be useful when the object is to obtain great
propelling power combined with strength, and such cylindrical portion
would further act as a guard to prevent ropes or other floating matters
obstructing the action of the instrument, especially on the navigation of
canals. I should further remark, that I do not limit myself to the
precise proportion of the centrifugal or other curves described; and
though I have found and of the radius of the propeller to answer
for the radius of the centrifugal and backing curves, I think that the
radius of such curves should not exceed 3rd nor be less than th
of the radius of the instrument; the propeller to be fitted to the
stern of the vessel to be propelled, or to any other part of the vessel
on the plans known to be effective, and worked by steam, caloric,
or other motive power. One of the advantages claimed for this pro-
peller is that of effectually propelling the vessel on a smaller draught

page_text: of water, or with a propeller of smaller diameter, and the limit of the
reduction of the diameter would depend in a great measure on the
form of the vessel to be propelled; but, as a general rule, the diameter
should not be less than that which would produce a greater slip than
thirty-three per cent. in calm weather.
Now I claim as my Invention the improved propeller, and the com-
bination of any two or more of the parts or elements for the purpose
of propelling vessels, and also such modification thereof, as before
described.
In witness whereof, I, the said Charles Augustus Hohn, have
hereunto set my hand and scal, this Twenty-fourth day of
Sepember, in the year of our Lord One thousand eight hundred
and fifty-three.
C. A. HOLM. (L.S.)
Witness, S. CARPMAEL.