Year: 1899

page_text: I, HORATIO FRANCIS SMYTH, of the Junior Army and Navy Club, Saint James
Street, London, W., Lieutenant-Colonel Royal Artillery, Retired, do hereby
declare the nature of this invention to be as follows:-
This invention relates to improvements in screw propellers and has for its
object the better distribution of the propelling blades, and their relative pitches
upon the driving shaft, so as to induce an increased speed of propulsion from
a given power, greater than has hitherto been achieved by the ordinary pro-
peller, by reason of the relative reinforcement and distribution of effort of two
or more combined propellers on one shaft.
To carry out my invention, I provide at least two distinct propellers on one
shaft, approximately similar, being alike in area, diameter, and shape: but
(a) The pitch of the fore propeller is about 10 per cent. finer than the pitch
of the after propeller, the after propeller having its pitch similar to that of the
ordinary type propeller deemed best suited for the particular vessel under con-
sideration to which my propeller always bears a direct reference.
(b) The relative position of the two propellers on the shaft is such that the
blades of the after propeller are clear of being covered by the corresponding
blades of the fore propeller. Each blade in the rear propeller with this object
moves in advance and about clear from being covered by its corresponding
blade in the fore propeller; or alternatively the corresponding blades of the
after set may follow, but not be covered by, those of the fore propeller.
(c) The total area of all blades of my divided propeller is in excess of the total
area of the ordinary propeller blades for any particular vessel by about
25 per cent.
I take th of such. increased area for each of my blade areas when in two
sets of propellers each set having 3 blades.
(d) The centre of effort or the largest transverse diameter of the blade I
place half way out towards the tip of the blade measured from the circum-
ference of the boss.
66
(e) In shape each of my divided propeller blades is approximately elliptical,"
only varying towards the root where necessary for strength of attachment.
(f) The diameter of the blades in both sets of my propeller is similar to the
diameter for the ordinary single propeller for the particular vessel under con-
sideration.
I have found beneficial effects result from my combined propellers when
constructed on the principles embodied in the above described method vz.:-
In increased speed, greatly reduced vibrations and diminished racing, and an
excellent go-astern power; whether they are fixed close together on the shaft
or at a distance from each other so that the blades of each set rotate in as
distinct paths as possible.
It is obvious I may combine more than two sets of propellers on the same

page_text: shaft, each set having 3 blades by following the above described method in
principle.
Dated this 10th day of 1800
123
FELL & JAMES,
1, Queen Victoria Street, London, E.C., Agents for the Applicant.
Improvements in Screw Propellers.
I, HORATIO FRANCIS SMYTH, of the Júnior Army and Navy Club, Saint James
Street, London, W.,. Lieutenant-Colonel Royal Artillery, Retired, 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 improvements in screw propellers as a development
upon any ordinary propeller at present in use or designed and assumed to be
the best propeller found most suitable for any particular ship, and has for its.
object the better distribution of the propelling blades, and their relative pitches
upon the driving shaft, so as to induce an increased speed of propulsion from
a given power, greater than has hitherto been achieved by the ordinary propeller,
by reason of the relative reinforcement and distribution of effort of two or more
combined propellers on one shaft.
To carry out my invention, I provide at least two distinct propellers on one
shaft, approximately similar, being alike in area, diameter, and shape; but
(a) The pitch of the fore propeller is about 10 per cent. finer than the pitch
of the after propeller, the after propeller having its pitch similar to that of the
ordinary type propeller deemed best suited for the particular vessel under con-
sideration to which my propeller always bears a direct reference.
..
(b) The relative position of the two propellers on the shaft is such that the
blades of the after propeller are clear of being covered by the corresponding
blades of the fore propeller. Each blade in the rear propeller, with this object,
moves in advance and about clear from being covered by its corresponding
blade in the fore propeller; or alternatively the corresponding blades of the
after set may follow, but not be covered by, those of the fore propeller.
(c) The total area of all blades of my divided propeller is in excess of the total
area of the ordinary propeller blades for any particular vessel by "about
25. per cent.
"
I take th of such increased area for each of my blade areas, when in two
sets of propellers, each set having 3 blades.
(d) The "
centre of effort," or the largest transverse diameter of the blade I
place half way out towards the tip of the blade, measured from the circum-
ference of the boss.
(e) In shape, each of my propeller blades is approximately "elliptical," only
varying towards the root where necessary for strength of attachment.
(f) The diameter of the blades in both sets of my propeller is similar to the
diameter for the ordinary single propeller for the particular vessel under con-
sideration.
:-
I have found beneficial effects result from my combined propellers, when
constructed on the principles embodied in the above described method, viz.:-
In increased speed, greatly reduced vibrations, and diminished racing, and an
excellent go-astern power whether they are fixed close together on the shaft,
or at a distance from each other, so that the blades of each set rotate in as
distinct paths as possible.

page_text: It is obvious I may combine more than two sets of propellers on the same
shaft, each set having three blades, by following the above described method
in principle.
In order that my invention may be the better understood, I now proceed
to describe the drawing, hereto annexed, as an illustration of the practical carry-
ing out of my improvement, as a development upon any ordinary single pro-
peller as already may be known.
Figure 1 is an elevation of my divided propeller, taken looking forward, two
blades, one out of each set, being shown complete.
Figure 2 is a developed view, in the flat, of one blade of my divided pro-
peller, as regards shape and section.
Figure 3 is a longitudinal section through my divided propeller, one blade
only out of each set being shown complete.
It is assumed that an ordinary single propeller (say with three blades or
with four) is already in use as the best propeller that can be devised for any
ship; or in case of a ship being built, the area, and pitch, of a single propeller
must be designed for such ship by the ordinary and well known formulæ or
rules.
This determines the pitch of the aft propeller A of my divided propeller
and the area of the 6 blades of my divided propeller which are in the gross 25%
more than the total area of the said single propeller. Each of the six blades
of my divided propeller being similar in area, will be th of the said total gross
area.
The forward propeller B has however a pitch 10%, finer than that of the aft
propeller as above determined.
The angle between the radial axes of the two corresponding blades A and B
(one out of each set), should subtend about 1th of the circumference of the
circle about the tips of the propellers.
The shape of the blades A and B is approximately elliptical as shown, with
the greatest transverse diameter, or centre of effort, situated half way out
towards the tip of the blade measured from the circumference of the boss C.
The bosses C are fixed upon the propeller shaft in the usual way.
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 I
claim is:-
1st. Divided screw propellers, in duplicate or in multiple upon the same
shaft, characterized, in combination, by each set of blades (having preferably
three blades in each set), being similar as to shape and area one to another;
the pitch of the fore propeller being ten per cent. finer than the propeller
situated aft to it, which has the pitch of the best ordinary propeller, of which
the divided propeller is a development; each blade of successive sets being just
clear of the corresponding blades of the other set or sets; the total area of the
divided propeller being in excess of the total area of single ordinary propeller
blades (of best adaptability to the ship) by about 25 per cent., the diameter of
the various propellers being the same; and the shape of each blade being ap-
proximately elliptical with the largest transverse width of each blade being
half way out towards the tip of the blade measured from the circumference of
the boss, substantially as and for the purposes described.
01
1
1000
FELL & JAMES,
1, Queen Victoria Street, London, E.C., Agents for the Applicant.