AN IMPROVED SCREW PROPELLER
Year: 1875

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Cliancery Lanc,
in the County of Middlesex, Patent Agent, for the Invention of
"AN IMPROVED SCREW PROPELLER."-A communication from abroad
by Elbert B. Porter, of Havana, in the Island of Cuba.
PROVISIONAL SPECIFICATION left by the said Alexander Melville
Clark at the Office of the Commissioners of Patents, with his
Petition, on the 22nd March 1875.
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, do hereby declare the nature of
the said Invention for "AN IMPROVED SCREW PROPELLER," to be as
follows:-
This Invention has for its object to furnish an improvement upon the
ordinary screw propeller, which may be constructed at less cost, more
conveniently and cheaply repaired when broken or injured, and capable
of producing a considerable increase of speed.
The Invention consists of a screw propeller with semi-elliptic or
otherwise bent and twisted blades attached at one or both ends to shaft,

page_text: and provided with interior and exterior auxiliary wings of sufficient size
and twist.
For lighter vessels it may be sufficient to attach one end of the screw
blades merely to the shaft, the other ends being rigidly connected; but
for larger vessels and heavier work it will be preferable to extend
the shaft centrally to the rear end of the blades and bolt them firmly
thereto.
The twisted blades may be curved in semi-elliptic, oval, or round
shape, as found most effective by experiment. They are furthermore
provided with interior and exterior auxiliary wings or blades of suitable
size, curve, and twist, which are firmly bolted under suitable inclination
near the middle and rear parts to the main blades for the purpose of
increasing the propelling surface without causing the dragging or
vibrating of any parts.
The inner auxiliary blades may, when desirable, be extended to the
shaft and bolted thereto at their inner ends.
The propeller is made of rolled metal plates, each auxiliary and main
blade being separately attached, so that any part may be repaired without
interfering with the other parts.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Alexander Melville Clark in the Great Seal Patent
Office on the 11th August 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-second day of March, in the year of
our Lord One thousand eight hundred and seventy-five, in the thirty-
eighth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Alexander Melville Clark, Her special
licence that I, the said Alexander Melville Clark, my executors, admini-
strators, and assigns, or such others as I, the said Alexander Melville
Clark, my executors, administrators, and assigns, should at any time

page_text: 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
"AN IMPROVED SCREW PROPELLER," a communication to me from abroad by
Elbert B. Porter, of Havana, in the Island of Cuba, upon the condition
(amongst others) that I, the said Alexander Melville Clark, my executors
or administrators, by an instrument in writing under my, 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 I, the said Alexander Melville Clark, 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, reference being had to accompanying Sheet
of. Drawings, and to the letters and figures marked thereon (that is to
say)
:―
This Invention has for its object to furnish an improvement upon the
ordinary screw propeller, which may be constructed at less cost, more
conveniently and cheaply repaired when broken or injured, and capable
of producing a considerable increase of speed.
The Invention consists of a screw propeller with semi-elliptic or
otherwise bent and twisted blades attached at one or both ends to a shaft,
and provided with interior and exterior auxiliary wings of sufficient size
and twist.
In the accompanying Drawings Figure 1 represents a side elevation
of the Invention; Figure 2, an end elevation of the same. In the above
examples of the Invention the diameter of the propeller is less than its
length; Figure 3 is a perspective view of the Invention in which the
diameter of the propeller is greater than its length. This form of
propeller is intended for use on vessels in which propellers of largo
diameter are needed. Similar letters of reference indicate corresponding
parts.
In the Drawing A represents the propeller shaft to which are attached

page_text: For lighter vessels it may be sufficient to attach one end of the screw
blades merely to the shaft, the other ends being rigidly connected; but
for larger vessels and heavier work it will be preferable to extend
the shaft centrally to the rear end of the blades and bolt them firmly
thereto.
The twisted blades B may be curved in semi-elliptic, oval, or round
shape, as found most effective by experiment. They are furthermore
provided with interior and exterior auxiliary wings or blades C of
suitable size, curve, and twist, which are firmly bolted under suitable
inclination near the middle and rear parts to the main blades for the
purpose of increasing the propelling surface without causing the dragging
or vibrating of any parts.
The inner auxiliary blades may, when desirable, be extended to the
shaft A. and bolted thereto at their inner ends.
The propeller is made of rolled metal plates, each auxiliary and main
blade being separately attached, so that any part may be repaired without
interfering with the other parts.
Having described the nature of the Invention, and the manner of per-
forming the same, I would observe that I do not limit or confine myself
to the exact form or proportion of any of the parts here shown, as these
may be varied in many ways by the constructor without departing from
the Invention; but what I claim as the Invention to be protected by
the herein-before in part recited Letters Patent is, a screw propeller
constructed with semi-elliptic, curved, and twisted blades attached at
one or both ends to the shaft, and provided with projecting interior
and exterior auxiliary blades or wings, substantially in the manner and
for the purpose set forth.
In witness whereof, I, the said Alexander Melville Clark, have
hereunto set my hand and seal, this Eleventh day of August,
in the year of our Lord One thousand eight hundred and
seventy-five.