Improvements in Screw Propellers.
Year: 1893

page_text: Date of Application, 16th Mar-, 1893
Complete Specification Left, 15th Jan., 1894-Accepted, 17th Feb., 1894
+
Improvements in Screw Propellers.
I, JAMES BAXTER MURRAY, of 28 Herriet Street, Pollokshields, Glasgow,
Master Mariner, do hereby declare the nature of this invention to be as
follows:-
This invention relates to screw propellers for operation in water or air and it has
for its object to improve their construction.
i
Tho propeller consists of two blades which are somewhat semi-circular in shape
and arranged upon the boss, at, or about an angle of 40 degrees with each other
and so that the plane of each blade forms an angle of about 70 degrees with the
axis of rotation. The blades are soniewhat concave on the after or driving sides
and convex, or rounded, on the opposite sides. The pitch of each blade is an
increasing one, extending from the driving edge to the back edge of each blade.
The blades can be set at a greater or smaller angle to suit various classes of
vessels and the pitch can be made finer or coarser for the same purpose. The
pitch can, if desired, be made a decreasing one to suit any special form of vessel.
The blades are so arranged that a comparatively small boss is required as the
root of each blade almost embraces the semi-circumference of the boss and thus
forms a very strong connection.
The united area of the blades is, preferably, about of the area of the circle in
which they revolve.
The propeller is, preferably, made as one solid casting although, if so desired,
the blades may be made separately and be fitted to the boss.
The propeller blades are designed in such a manner that the power of the engines
may be spent as much as possible in moving the vessel.
.I
Water, under certain conditions, having somewhat of an elastic nature, one of
the objects of my propeller is to make the water for the time being, as much of a
solid body as possible which results in a very considerable reduction in slip.
The propeller can be fitted as an overhanging propeller or with an after bearing
if so desired.
With a propeller of this construction the revolutions will be reduced thereby
reducing friction on all working parts of machinery and shaft bearings, and, by its
steady uniform motion, will minimise the torsional strain on the propeller shaft and
will very considerably reduce the evil effects of racing, causing much less vibration
on account of the absence of thrashing or churning, thereby reducing the risk of
breaking shafts, stripping blades, etc.
Under the same engine power, if a propeller of this construction and of about
one third less diameter, be substituted for a full sized propeller of the present
type, the result would be an increase of about 15% in speed, with a considerable
reduction in the consumption of fuel, but, by increasing the diameter to the full
size, an additional gain of about 10%, will be obtained, making a total of about
25% in favour of this form of propeller.
·
When this propeller is substituted for one of the existing type, the revolutions
per minute are somewhat reduced, but, from the small percentage of real and
apparent slip, each revolution propels the vessel much faster, and enables her to
cover any given distance in from 15 to 20 per cent. less time with a corresponding
reduction in the expenditure of fuel.
-
My propeller has the following advantages :—
1. The maximum of speed, with the minimum of slip, resulting in a reduction in
the revolutions na minvitalish
dud nanoumution of fl

page_text: 2. The racing of engines is reduced thereby reducing the effects of same and
also reducing the risk of breakage of shafts, or stripping the propeller blades.
3. A comparatively light propeller, combined with great strength, large area,
and small diameter.
4. Reduces the revolutions per minute, and, as a consequence, a considerable
reduction in tear and wear of all working parts is obtained.
5. Is not so liable to be damaged by coming in contact with hard substances.
6. A powerful propeller in driving ahead and equally powerful in quickly
stopping a steamers bead-way, by reversing the engines.
7. As the working is steady and uniform without thrashing or churning,
vibration and torsional strain, especially in after length of shafting in stern tube,
is considerably reduced.
Although have described the propeller as for use in water it is equally suitable
for operating in air as a blower or air propeller.
Dated this 15th day of March 1893.
H. D. FITZPATRICK,
70, Wellington Street, Glasgow, Agent.
COMPLETE SPECIFICATION.
Improvements in Screw Propellers.
1, JAMES BAXTER MURRAY, of 28 Herriet Street, Pollokshields, Glasgow,
Master Mariner, 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 :-
This invention relates to screw propellers for operation in water and it has for
its object to improve their construction.
And in order that my said invention may be properly understood I have here-
unto appended an explanatory sheet of drawings, which show, by way of example,
one form of my propeller.
Fig. 1 is an end view of the propeller.
Fig. 2 is a plan of the propeller.
The propeller consists of two blades a, b which are somewhat semi-circular in
shape and arranged upon the boss preferably at or about an angle of 70 degrees
with each other, and so that the plane of each blade, at the driving edge c, forms
an angle of about 55° with the axis of rotation. The blades are somewhat con-
cave (as shown at Fig. 2) on the after or driving sides and convex, or rounded,
on the opposite sides. The blades are so bent or twisted that the pitch is an
increasing one (i.e. coarser), extending from, say, 55° at the driving edge cto,
say, 45° at the back or tail edge d of each blade. As will be seen the blades
gradually taper away from the maximum breadth, measured radially from the
boss, at the tail end at d to the minimum breadth at the entering part cl, of
the driving end. This construction makes the blades appear, as at. Fig. 1, lop
sided, ie, with the tail end of a much greater superficial area than the driving
end.
The blades can be set at a greater or smaller angle to suit various classes of
vessels, and the pitch can be made finer or coarser for the same purpose. The
pitch can if desired be made a decreasing oue to suit any special form of
vessel:
:
As will be seen the blades are so arranged that a comparatively small boss is
required the root of each blade almost embracing the semi-circumference of the
boss, and thus forming a very strong connection.
The propeller is preferably. made as one solid casting, although, if so desired,
the blades may be made separately and be fitted to the boss..

page_text: The propeller blades are designed so as to use as much of the power of the
engines as possible in moving the vessel.
Water under certain conditions having somewhat of an elastic nature, one of the
objects of my propeller is to make the water for the time being as much of a solid
body as possible which results in a very considerable reduction in slip.
The propeller can be fitted as an overhanging propeller or with an after bearing
if so desired.
A propeller of this construction reduces the number of revolutions and as a
consequence reduces friction on all working parts of machinery and shaft bearings,
and its steady uniform motion, minimises the torsional strain on the propeller shaft
and very considerably reduces the evil effects of racing. On account of the absence
of thrashing or churning there is much less vibration and consequent risk of
breakage of shafts, stripping of blades etc.
The result of experiments, so far, have shown, that, under the same engine
power, if a propeller of this construction and of about one third less diameter, be
substituted for a full sized propeller of the present type, there will be an increase
of about 15% in speed with a considerable reduction in the consumption of fuel,
but by increasing the diameter to the full size an additional gain of about 10%
will be obtained making a total of about 25% in favour of this form of propeller.
Experiments have also shown, that, when this propeller is substituted for one of
the existing type, the revolutions per minute are somewhat reduced, but from the
small percentage of real and apparent slip each revolution propels the vessel much
faster, and enables her to cover any given distance in from 15 to 20 per cent. less
time with a corresponding reduction in the expenditure of fuel.
My propeller has the following advantages:
1. The maximum of speed, with the minimum of slip, resulting in a reduction in
the revolutions per minute with a reduced consumption of fuel.
2. The racing of engines is reduced thereby reducing the effects of same and also
reducing the risk of breakage of shafts or stripping the propeller blades.
3. A comparatively light propeller, combined with great strength, large area,
and small diameter.
4. Reduces the revolutions per minute and as a consequence a considerable
reduction in tear and wear of all working part is obtained.
5. Is not so liable to be damaged by coming in contact with hard substances.
6. A powerful propeller in driving ahead and equally powerful in quickly
stopping a steamers headway, by reversing the engines.
7. As the working is steady and uniform without thrashing or churning, vibration
and torsional atrain, especially in after length of shafting in steam tube, is
considerably reduced.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
consider novel and desire to claim is :-
A two bladed propeller, constructed substantially as hereinbefore described with
reference to the drawings annexed.
Dated this 13th day of January 1894