Year: 1897

page_text: Date of Application, 9th Aug., 1897
I, JOHN MARSHALL, of 28, Brasenose Road, in the Borough of Bootle-cum-
Linacre, in the County Palatine of Lancaster, Civil & Mechanical Engineer, do
hereby declare the nature of this invention to be as follows:-
In the place of the solid blade as at present applied in the construction of
screw propellers; I substitute a hollow blade, this hollow blade has an opening
into it, close to the boss, which opening is placed at or about, a mean angle with
the keel line of the ship, or the line representing the velocity of the ship, and a
lino at right angles thereto representing the circumferential velocity of the propeller
at the diameter represented by the aforesaid opening into the hollow blade. At the
tip of the blade or extreme diameter which tip is bent backwards in a direction
towards the stern, I place another aperture in the aforesaid hollow blade this
aperture is placed so as to stand in such a position that the water after being
forced through the hollow blade by the centrifugal velocity of the propeller shall
be propelled backwards in a line as nearly as possible with the fore and aft line
of the ship.
This hollow system of construction can be applied to almost any form of
blade.
The action of this propeller is as follows as the propeller is revolved in the
ordinary manner, the water near the boss, enters the hollow blade by the aperture
provided for that purpose where it receives considerable centrifugal velocity and
is expelled from the aperture at the tip of the blade in a line as nearly directly
aft as may be with a force proportionate to the circumferential velocity of the tip
of the blade.
By thus taking advantage of the centrifugal force already existing in the
propeller due to its circumferential velocity, I not only obtain the propelling forec
due to the action of the propeller as a screw but the thrust of the water due to its
centrifugal velocity acting as a turbine proportionate to the velocity of the tip of
the propeller blade.
By placing the outlet at the tip of the blade in such a position that the water
issues at or about right angles to the line of the ship's motion the centrifugal force
of the water will assist the engines in forcing the propeller through the water,
but under this condition would not act as a direct propeller to the ship.
To give full effect to this kind of propeller various kinds, forms and angles of
orifices may be required to suit the different conditions of the ship and engines.
Doted this 7th day of August 1897.

page_text: Improvements in Screw Propellers.
I, JOHN MARSHALL, of 28, Brasenose Road, in the Borough of Bootle-cum-
Linacre, in the County Palatine of Lancaster, Civil and Mechanical Engineer,
do hereby declare the nature of this invention and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement:
-
In the place of the solid blade as at present employed in the construction of
screw propellers, I substitute a hollow blade. This hollow blade has an opening
in it, at or near to the boss, which opening is placed at or about a mean angle with
the keel-line or a line representing the velocity of the ship and a line at right
angles thereto, representing the circumferential velocity of the propeller at the
diameter represented by the aforesaid opening in the hollow blade.
At or near the tip of the blade or extreme diameter, which tip is bent aft, I
place another aperture in the aforesaid hollow blade. This aperture is placed in
such a position that the water after being forced through the hollow blade by the
centrifugal velocity of the propeller, shall be propelled backwards in a line as
nearly as possible coinciding with the fore-and-aft line of the ship.
This hollow system of construction can be applied to almost any form of blade.
The action of this propeller is as follows, reference being had to the annexed
drawing in which Figure 1 is an after elevation, Figure 2 a forward elevation,
and Figure 3 a starboard elevation of one blade of a propeller constructed according
to my invention. a is the water inlet aperture, 6 the water outlet aperture,
and c is the bent tip of the blade. As the propeller is revolved in the ordinary
manner the water near the boss, enters the hollow blade by the aperture a, provided
for that purpose, where it receives considerable centrifugal velocity and is expelled
from the aperture 6 at the tip c of the blade in a line as nearly directly aft as
may be, with a force proportionate to the circumferential velocity of the tip of
the blade.
By thus taking advantage of the centrifugal force already existing in the pro-
peller, due to its circumferential velocity, I not only obtain the propelling force
due to the action of the propeller as a screw but the thrust of the water due to its
centrifugal velocity acting as a turbine, proportionate to the velocity of the tip
of the propeller blade.
To give full effect to this kind of propeller, various kinds, forms, and angles of
orifices a and b may be required, to suit the different conditions of the ship and
engines.
Having now particularly described and ascertained the nature of my inven-
tion, and in what manner the same is to be performed, I declare that what 1
claim is:-
:-
A screw propeller whose blades are hollow and provided with inlet and outlet
apertures, disposed substantially as herein described, whereby the water around
the boss of such propeller enters such hollow blades and is ejected from the tips
thereof, substantially as and for the purpose herein described.
Dated 171 1.
JJ
1000
J. A. COUBROUGH,
Chartered Patent Agent,
10, St. George's Crescent, Liverpool, Agent for the Applicant.