IMPROVEMENTS IN SCREW PROPELLERS
Year: 1871

page_text: LETTERS PATENT to Henry Zahn, of San Francisco, California, in
the United States of America, for the Invention of "IMPROVEMENTS
IN SCREW PROPELLERS."
Sealed the 29th September 1871, and dated the 12th August 1871.
COMPLETE SPECIFICATION filed by the said Henry Zahn at the Office
of the Commissioners of Patents, with his Petition and Declaration,
on the 12th August 1871, pursuant to the 9th Section of the
Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRY
ZAHN, of San Francisco, California, in the United States of America,
send greeting.
WHEREAS I am in possession of an Invention for "IMPROVEMENTS
IN SCREW PROPELLERS," and have made solemn Declaration that I verily
believe myself to be the true and first Inventor thereof.
NOW KNOW YE, that I, the said Henry Zahn, do hereby declare'
that the following Complete Specification, under my hand and seal,

page_text: fully describes and ascertains the nature of my said Invention, and in
what manner the same is to be performed :-
My improvements in screw propellers consist, first, in a novel
arrangement of the wings or blades by which two threads are cut in
the water in different planes at each revolution of the propeller, and, 5
secondly, in the peculiar curve of the blades by which the propeller
is allowed to exert its full driving power without creating a sufficient
back current to impede the rear or following threads of the screw.
In order to describe my improved construction of screw propellers
in a proper manner a full description is given below with reference to
the accompanying Drawings, in which Figure 1 is an illustration of a
propeller fitted with four blades arranged in a V form and carried upon
two hubs; Figure 2 is a modification of the same but with blades
arranged in an X form, and carried upon one long hub; Figure 3
represents the application of the blades arranged in the V form to one
short hub.
added as may be
A represents the hub from which the propeller blades radiate and
which is keyed upon the shaft in the usual manner. Upon this hub are
fixed four blades b, c, d, e, or as many more may be
desired. These blades are arranged upon the hub so as to stand at
an angle alternately in opposite directions, that is, the blades b, d, which
are upon opposite sides of the hub A, stand obliquely to it in the
same direction, while the blades c, e, stand obliquely to it in the
opposite direction, thus causing the two sets of blades to cut two threads
in the water in a V form. The blades b, c, d, e, are slightly twisted
from their bases to their points, thus giving them a slight concavity
on their inner faces at the middle of the blades while the outer face
is convex and proportioned to the curve traversed. An opposite twist
is given to each alternate blade so as to cause each one to drive the
water or current which it creates in a line parallel with the currents
produced by the other blades and in a direction oblique from the shaft
upon which the propeller is fixed, as indicated by the arrows, so that
the current or commotion produced by one blade will not affect the
blade following it, but each one will move in a solid body of water,
and thus exert its greatest power. If it should be found desirable that
the propeller should
the hub A could be made longer
less space
occupy
as shown at Figure 2, and the blades be fixed to it so that the two
sets will cross cach other in the form of an X as shown. In this case

page_text: the two threads cut by the two sets of blades will also cross each other
in the form of an X. Each set of blades in either case can be secured
to a separate hub and the two hubs fixed upon the same shaft at the
proper distance apart, thus doing away with a considerable weight of
extra and useless metal.
By constructing screw propellers in the manner above recited the
wallowing of the blades in an agitated body of water is avoided, con-
sequently greater speed can be obtained from a screw of the same
dimension than can be obtained from the ordinary screw.
Having thus described my Invention, what I claim and desire to
secure by Letters Patent is,-
First. In a screw propeller arranged to cut two threads in the water
I claim arranging the blades in opposite directions alternately so as to
represent either the V or X form, substantially as and for the purpose
above described.
Second. Giving to each alternate blade an opposite twist, substantially
as and for the purpose above described.
In witness that the above-described Invention is claimed by me,
I have hereunto set my hand and scal, this Twentieth day of
July, in the year of our Lord One thousand eight hundred and
seventy-one.
Witnesses,
JOHN L. BOONE,
WM. GERLACH.
HENRY ZAHN. (L.S.)