A NEW OR IMPROVED MEANS FOR INCREASING THE THRUST OF SCREW-PROPELLERS
Year: 1879

page_text: LETTERS PATENT to John Mackenzie, of Stockton on Tees, in the County of
Durham, Engineer, for the Invention of "A NEW OR IMPROVED MEANS FOR
INCREASING THE THRUST OF SCREW-PROPELLERS,"
Sealed the 19th August 1879, and dated the 18th April 1879.
PROVISIONAL SPECIFICATION left by the said John Mackenzie at the Office
of the Commissioners of Patents on the 18th April 1879.
JOHN MACKENZIE, of Stockton on Tees, in the County of Durham, Engineer.
"A NEW OR IMPROVED MEANS FOR INCREASING THE THRUST OF SCREW PRO-
PELLERS.
The means or appliances hitherto adopted for increasing the working power of
a screw propeller, and thereby reducing to a minimum the positive slip of the
screw, have been numerous and as yet unsatisfactory, proving either costly in
carrying out or defective in their results, or both oostly and defective.
To remedy these objections is the purpose of my said Invention, which I will now
briefly describe. Upon the stern post of the vessel to which my Invention is pro-
posed to be fitted, and encircling the ship's screw propellor, which may be of any
ordinary type, I fix vertically an open framework composed of, say, six radial arms
of a length sufficient to extend (radially) beyond the blades of the screw propellor.
The extremeties of the said radial arms are turned or bent at right angles and over
the blades of the screw propeller, and thus prevent the water being dispersed tan-
gentially or centrifugally when the screw propellor is in motion, but cause the said
water to take a direction in a line with the vessel's keel, and the ship to pursue a
direct course.
A similar result to the above might follow if the open frame work, instead of being
fixed to the stern post of the vessel, as before described, were allowed to revolve
loosely upon the propeller shaft by the action of the water due to the ship's
progress.
When applying my Invention to the present arrangement of a ship's screw pro-
peller little or no alteration is required thereto.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Mackenzie in the Great Seal Patent Office on the 18th
October 1879.
JOHN MACKENZIE, of Stockton-on-Tees, in the County of Durham, Engineer.
"A NEW OR IMPROVED MEANS FOR INCREASING THE THRUST OF SCREW-
PROPELLERS."
The means or appliances hitherto adopted by marine engineers for increasing
the working power of a screw propeller, and thereby reducing to a minimum
the positive slip of the screw, have been numerous and as yet unsatisfactory,
proving either costly in carrying out or defective in their results, or both costly and
defective.
The means I employ to remedy these defects may be briefly explained as
follows:-
Upon the stern post or upon any other suitable part of the vessel to which my
Invention is proposed to be fitted I fix vertically and in a manner encompassing the
ship's screw propeller, which may be of any ordinary type, an open framework com-
posed of, say, six radial or eccentric arms, each of a length sufficient to extend
(radially) beyond the blades of the screw propeller. The inner extremeties of these
arms are secured to the said stern post; the outer ends are however turned or bent
over the tip of the blades of the screw. They prevent the water being dispersed
tangentially when the screw propeller is in motion, but cause the water to take a
direction in a line with the vessel's keel, and the ship to pursue a direct course, thus
avoiding the necessity of constantly keeping the rudder "over" in one direction, as
is usually the case, which entails a drag on the ship and occasions an unprofitable
expenditure of engine power.
A similar result to the above might follow if the open framework before described,
instead of being fixed to the vessel, were allowed to revolve loosely upon the pro-
peller shaft by the action the water due to the ship's progress.
I have found by experimental trial on the S.S. "Shannon," of Blyth, that my In-
vention, which I call a "propeller assistant," prevents that useless motion of the
water observed when a screw steamer lightly laden is in motion, and greatly con-
tributes to the effect of the propeller acting as a screw working in a solid.
In Figure 1 of the accompanying Drawing I have shewn a perspective view of
a small vessel fitted with my Invention, Figures 7 and 8 being enlarged geometrical
views of the same; the former is a sectional elevation on line 5*-6* (see Fig. 8),
and the latter a transverse section on line 7* -8× (see Fig. 7). In all these Figures
a', a³, a³, a', a³, and a are the radial or eccentric arms. In this case I have shown
them as being eccentric, or more correctly speaking tangential, they being tangents
to an imaginary small circle describe about the axis of the propeller shaft. The
inner ends of these arms are bolted to a casting B (see also enlarged details, Fig. 6)
secured to the stern post C of the vessel, while the outer extremeties are rendered
firm and ridgid by being secured to the inner surface of the ring or hoop d, d,
encircling the screw propeller and secured to the stern post framing, as shown in
Fig. 8. This mode of construction readily admits of my Invention being applied to
any present arrangement of ships' screw propellers, and necessitates little or no
alteration of parts.
The dotted lines in Figure 7 represent the position of the screw, and it will be
here observed how the outer end of the arm a¹ is bent over to cover the tip of the
blade of the screw. The shape of the arms consequently depend in a great ineasure
upon the form and dimensions of the screw to which my Invention is intended to
be applied, but by shaping the arms to suit the screw the principle of my Invention
is made applicable to any type of screw propeller.

page_text: The views in Fig. 6 are enlarged details of one half of the casting B (Fig. 7); the
portion bin duplicate are bolted one on either side of the stern post, and to the
parts e, e, e, are secured the arms, as shown in Fig. 8.
Figure 2 is a perspective view of a modification of my Invention, and may be
suitable for sea going boats of deep draught. In construction it is less expensive
than the former method, and may be applied to any suitable ship without loss of
time through docking.
Figs. 3 and 4 are enlarged geometrical views, the former being a transverse
section on line 1*-2* (Fig. 4), looking forward, and the latter Figure a longitudinal
elevation, Figure 5 being a sectional plan or line 3*-4*, Fig 3. In all these
Figures the propeller is removed to render the Drawing more clear.
In this modification it will be observed that the casting B in Figs. 7 and 8 is here
dispensed with, and the arms, instead of being tangential, are obliquely radial;
starting from the stern post to which they are bolted, they meet at the point f, and
uniting form the arc d*, d*, which is bolted to the vessel as shown, and similar to
the hoop d, d, Fig. 8.
Although I have shown my Invention adapted to existing screw steamers, it is of
course understood that my Invention is equally applicable to screw steamers in course
of construction; in that case any suitable number of arms may be employed, and
they may be rigidly secured by other means than by the two semi-hoops d, d, Fig. 8,
or by the semi arcs d*, dx, Fig. 3. Any ordinary mechanic would readily conceive
a suitable mode of applying and fastening these arms to meet the requirements of
any particular build of ship or peculiar type of screw propeller.
Having now particularly described the nature of my said Invention, together with
the means of carrying the same into practical effect, I wish it to be understood that
I claim as my Invention secured to me by the above in part recited Letters Patent,
the means for increasing the thrust of screw propeller, substantially as and in the
manner above described, and shewn upon the accompanying Drawing, or any mere
modifications thereof.
In witness whereof, I, the said John Mackenzie, have hereunto set my hand
and seal, this Seventeenth day of October, in the year of our Lord One
thousand eight hundred and seventy nine.
JOHN MACKENZIE (Ls.)