Improvements in Screw Propellers.
Year: 1896

page_text: PROVISIONAL SPECIFICATION.
Improvements in Screw Propellers.
I, WILLIAM GLASS WRENCH, of 27 Oswald Street, Glasgow, in the County of
Lanark, Consulting Engineer, do hereby declare the nature of this invention to be as
follows:-
total area.
This invention has for its object to adapt screw propellers for being driven by
dynamos, steam turbines or other kindred motors of high rotative speed which may
be used for the purposes of propulsion, and to which the existing types of propellers
of large diameter, short length, and few blades are unsuitable. Should the speed of such
motors be (say) ten times more than that now obtained with the present reciprocating
types of engines I purpose in the first place, under this invention, to diminish the
propeller's diameter so that the usual peripheral speed relatively to that of the vessel
can only be acquired by the higher number of revolutions and secondly to give
exceptional length to this propeller to make up for its deficiency in diameter. In the
third place to avoid anything like a continuous convolution of thread with such a
long propeller, I purpose stepping a large number of very small, blades or fins at
due intervals, either zigzag or in longitudinal rows throughout the length of its
elongated boss, such number to depend upon the predetermined diameter of the
propeller and the area of each blade which will represent but a small fraction of the
The improved propeller will therefore essentially consist of a series of
very small propellers placed one behind the other upon the shaft, ranging from three
in number upwards, and the minimuin total length of this propeller may not be less
than of its diameter while the spacing of the blades shall not generally be nearer
to each other in a fore aft line than their longitudinal projected widths, but more if.
necessary. The blade area of each of the series of propellers should bear a much less
proportion to the disc area than what now prevails in practice, but the total flat
area of all the blades should more than cover the disc. The length of the blades from
root to point should not exceed the diameter of the boss, unless where the solid end of
the shaft represents the boss and is abnormally small, but they may be one fourth of
this length, the object in making them so short being to bring up the root speed
relatively to that of the points and obtain a more uniform efficiency throughout their
area. They are also to be made very narrow relatively to the propeller disc, so as to
give but a momentary impact, and avoid prolonged frictional disturbance of the same
particles of water. The boss may either be the solid end of the shaft or a long sleeve
fitted thereon or upon its end having the blades tapped or dove-tailed into or riveted
or bolted upon it; or it may consist of a series of bosses each carrying its own set of
blades, cast on or attached thereto, and screwed, keyed or cottared up together
on the shaft with washers or suitable rings between each, if necessary, to serve
for jointing or to regulate distances. The general form of the boss throughout
is preferably that of a long cone, having either a curved or a straight taper
towards the smaller or after end, upon which the blades may be placed either radially
or with their acting or after faces inclined towards the axis, or otherwise sectionally
at about right angles or less to the slope of the boss, the inclination of each, whether
straight or curvated; increasing (if necessary) with each successive propeller towards
the after end of the boss which may either be made parallel, cigar shaped or otherwise
without affecting the increasing angular throwback of the blades towards the propeller's

page_text: rear end, as described. In some cases the throwback arrangement may be reversed,
i.e. the forward blades may be most inclined aft, and the after ones made nearer
radial. The blades may also be set with their points preferably leading circum-
ferentially and their pitch may either be true or variable or such as would result
from a perfectly flat surface and either kept uniform throughout the series, or
increased slightly towards the after end. They may also have any outline but (by
preference) will narrow in width from root to point rounding off at the roots
somewhat to prevent any undue width at their junction with the boss.. Or otherwise
the blades may each be in the form of quadrantal bends as described in the Specification
. of my Patent No. 831 of 1878.
.
The improved propeller should be capable of rotating at thousands of revolutions
per minute and attain a much higher peripheral velocity than that obtained in present
practice without throwing its blades away centrifugally. Its construction is based on
the principle that the greater the number of revolutions the smaller the diameter
required, and the greater proportional length and number of relatively diminished
blades. Its adaptation to vessels provided with single, twin or multiple screws permits
of lower and closer shaft centres, and a better immersion than heretofore practicable.
From one to five blades may be pitched on the circumference of any one of the series
of propellers forming the whole whether the boss is in one piece or made up in sectious
as described.
WALLACE FAIRWEATHER,
Chartered Patent Agent, 62 St. Vincent Street, Glasgow,
Agent for the Applicant.
Improvements in Screw Propellers.
I, WILLIAM GLASS WRENCH, of 27 Oswald Street, Glasgow, in the County of
Lanark, Consulting Engineer, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer
tained in and by the following statement :-
This invention has for its object to adapt screw propellers for being driven by
dynamos, steam turbines or other kindrad motors of high rotative speed which
may be used for the purposes of propulsion, and to which the existing types of
propellers of large diameter, short length, and few blades are unsuitable. Should
the speed of such motors be (say) ten times more than that now obtained with the
present reciprocating types of engines I purpose in the first place, under this
invention, to diminish the propeller's diameter so that the usual peripheral speed
relatively to that of the vessel can only be acquired by the higher number of
revolutions and secondly to give exceptional length to this propeller to make up
for its deficiency in diameter. In the third place to avoid anything like a continuous
convolution of thread with such a long propeller, I purpose stepping a large number
of very small blades or fins at due intervals either zig-zag or in longitudinal rows
throughout the length of its elongated boss, such number to depend upon the
predetermined diameter of the propeller and the area of each blade which will
represent but a small fraction of the total area. The improved propeller will therefore
essentially consist of a series of very small propellers placed one behind the other
upon the shaft, ranging from three in number upwards, and the minimum
total length of this propeller may not be less than of its diameter while the spacing
of the blades shall not generally be nearer to each other in a fore aft line. than their
longitudinal projected widths, but more if necessary. The blade area of each of the

page_text: series of propellers should bear a much less proportion to the disc area than what now'
prevails in practice, but the total flat area of all the blades should more than cover
the propeller's disc. The length of the blades from root to point should not exceed
the diameter of the boss, unless where the solid end of the shaft represents the boss
and is abnormally small, but they may be only one fourth of this length, the object
in making them so short being to bring up the root speed relatively to that of the
points and obtain a more uniform efficiency throughout their area. They are also to
be made very narrow relatively to the propeller disc, so as to give but a momentary
impact, and avoid prolonged frictional disturbance of the same particles of water.
The boss may either be the solid end of the shaft or a long sleeve fitted thereon, or
upon its end and having the blades tapped or dove-tailed into or riveted or bolted
upon it; or it may consist of a series of bosses each carrying its own set of blades,
cast on or attached thereto, and screwed, keyed or cottare up together on the shaft
with washers or suitable rings between each, (if necessary,) to serve for jointing or to
regulate distances. The general form of the boss throughout is preferably that of a
long cone, having either a curved or a straight taper towards the smaller or after end,
upon which the blades may be placed either radially or with their acting or after
faces inclined towards the axis, or otherwise sectionally at about right angles or less
to the slope of the boss, the inclination of each, whether straight or curvated, increasing
(if necessary) with each successive propeller towards the after end of the boss which
may either be made parallel, cigar shaped or otherwise without affecting the increasing
angular throwback of the blades towards the propeller's rear end, as described. In
some cases the throwback arrangement may be reversed, i.e. the forward blades may
be most inclined aft, and the after ones made nearer radial. The blades may also be
set with their points preferably leading circumferentially and their pitch may either
be true or variable or such as would result from a perfectly flat surface and either
keep uniform throughout the series, or increased slightly towards the after end.
They may also have any outline but (by preference) will narrow in width from root
to point rounding off at the roots somewhat to prevent any undue width at their
junction with the boss. Or otherwise each blade may be in the form of a quadrantal
bend as described in the Specification of my Patent No. 831 of 1878.
This improved propeller should be capable of rotating at thousands of revolutions per
minute and attain a much higher peripheral velocity than that obtained in present
practice without throwing its blades away centrifugally. Its construction is based on
the principle that the greater the number of revolutions the smaller the diameter
required, as well as its greater proportional length, and the number of relatively
diminished blades. Its adaptation to vessels provided with a single, twin or multiple
screws permits of lower and closer shaft centres, and a better immersion than heretofore
practicable. From one to five bladés may be pitched on the circumference of any
one of the series of propellers forming the whole, whether the boss is in one piece or
made up in sections as described.
In the accompanying drawings which illustrate the invention,
Figure 1 is a longitudinal section showing a modification of the improved propeller
in which the small blades A are attached to a long and rearwardly tapering single
sleeve or boss B secured upon the propeller shaft C. In this example the blades
nearest the forward end of the propeller boss are inclined most aft and the inclination
of the succeeding rows of blades gradually diminishes until at the after row the blades
are at right angles or thereby to the boss or axis, but the rake or inclination of such
blades may be reversed.
Figure 2 is a sectional elevation, Figure 3 a plan and Figure 4 an end view of a
modification in which the propeller is made up of a number of bosses B each carrying
its own set of blades A. In this case the bosses B gradually diminish in diameter
from the forward to the after end and the blades A being practically of the same
radial dimensions throughout, the propeller as a whole tapers gradually aft.
boss or bosses of the propeller may however be parallel throughout and the blades
made of equal length or even gradually reduced in length towards the after end.
The

page_text: The blades in this example are at the forward end approximately radial or perpen-
dicular to the surface of the boss, and towards the after end they are most inclined
aft, but the rake or inclination of such blades may be in this case also reversed.
Figure 5 is a part end view showing in full and dotted lines the relative proportions
approximately of blade and boss as made under my invention and such as is ordinarily
provided in existing propellers.
Figure 6 is a part end view of the improved propeller made with the blades in
the form of quadrantal bands as described in the specification of my former patent
above referred to.
Figure 7 is a diagrammatic representation of the stern part of a twin screw steam-
ship as fitted with this improved propeller and Figures 8 and 9 are like views of
single screw steamers showing this improved propeller applied thereto.
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
claim is―
A propeller expressly and exclusively adapted for being driven by high speed
dynamos, turbines and like rotary motors, and constructed substantially as described
with an extremely elongated boss or series of bosses having secured thereon a large
number of short and narrow screw-like blades or fins so as to form in effect a series
of propellers of very small diameter placed one behind the other on the propeller
shaft, but whose combined blade area relatively to power or vessel's displacement is
not intended to exceed that of an ordinary screw propeller.
Dated this 28th day of Annil 1807
WALLACE FAIRWEATHER,.
Of the Firm of Cruikshank and Fairweather,
Chartered Patent Agents, 62 St. Vincent Street, Glasgow,
Agent for the Applicant.