Improvements in Screw Propellers.
Year: 1896

page_text: Date of Application, 23rd Sept., 1896.
Complete Specification Left 23rd June 1897-Accepted. 23rd Oct., 1897
Date of Application, 23rd Sept., 1896.
Complete Specification Left 23rd June 1897-Accepted. 23rd Oct., 1897
Improvements in Screw Propellers.
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 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, and the pitch of the outer or rearward propeller may be slightly greater
than that of the preceding' propeller.
I have found also that the relative position of the blades of these two or more
propellers must be so, that one set of blades is situated in the interval between
that of the other blades.
I have found also that in comparison with the area of an ordinary single pro-
peller, I arrange for best results that the area of each of my duplicate propellers is
in excess of half but less than the complete area of one of the blades of an ordinary
single propeller.
I have found also that a beneficial effect results from my combined propellers,
whether the propellers are fixed close together upon the shaft, or at a distance
from each other, so long as the blades rotate in separate planes of revolution and are
in distinct and seperate spiral paths about the shaft.
It is obvious that I may increase the number of propellers, reinforcing one
another, care being taken, in such case, that the blades of the respective pro-
pellers break intervals with those immediately preceding them, and that the area
of the blades is reduced as compared with an ordinary propeller proportionately
to the number of reinforcing propellers used by me.
Dated this 23rd day of September 1896.
FELL & JAMES,
Agents for the Applicant.
Improvements
Propeners.
I, HORATIO FRANCIS SMYTH, of the Junior Army and Navy Club, St. James's
Street, London, S.W., Lieutenant-Colonel, Royal Artillery (Retired) do hereby
declare the nature of this invention and in what manner the same is to be per-
Dice T

page_text: formed to be particularly described and ascertained in and by the following
statement:
This invention relates to improvements in screw propellers, and has for its
object the better distribution of the propelling blades in divided sets upon the
propeller shaft, with specific arrangements as to surface of blades and modification
of pitch, so as to induce an increased speed of propulsion or power of draught from
a given power than has hitherto been achieved by the ordinary propeller and a
reduction of vibration upon the hull by reason of the relative reinforcement and
distribution of effect of two or more propellers on one shaft.
And in order that my invention may be the better understood, I now proceed
to describe the same, reference being had to the drawings hereto annexed and
to the letters and figures marked thereon.
Figure 1 is a longitudinal section through my improved divided propellers on
the same shaft.
Figure 2 is an end view thereof, and
Figure 3 is a plan of same.
To carry out my invention I provide at least two distinct propellers A and B on
one shaft C, and the pitch of both propellers may be a little coarser than would
be the case in the ordinary propeller for any particular vessel, and both pro-
pellers may have the like pitch, or the pitch of the outer or rearward propeller
may be slightly greater than that of the preceding propeller.
Well known rules exist for ascertaining the dimensions of single propellers,
given the dimensions of the ship. Such a rule for instance is the following:
mid-ship section
that the area of a single propeller as a disc=
This will give a
diameter of such disc.
3.5
The pitch of such propeller would be the diameter as aforesaid x by 1 to 1
according to the speed of the projected ship from that of a "tramp" to a high
speed "Liner." The surface of the blade of an ordinary propeller would then be
approximately of the pitch measured longitudinally on the shaft, multiplied
by the radial length of the blade from the root to the tip.
Or, alternatively, the area of an ordinary screw blade may be found from the
indicated horse power and the revolutions, by the following well known formula:-
Area of total blades - K✔
where K is 13 for a single three bladed
Ind. H.P.
Revolutions
propeller and 9 for twin 3 blade propellers.
The above represents substantially the results of experience with regard to a
single propeller. Now in my invention. I substitute two or more propellers on the
same shaft for a single propeller, properly proportioning them according to my
invention, the utility and efficiency of which depends on two essential points.
1st. That the area of each of my divided propeller blades A and B is less than
that of an ordinary single propeller blade for the same vessel, but their aggregate
area is greater. For instance, if I use two propellers, the area in each of my
blades will be in excess of the area of an ordinary single blade of a propeller
having the same number of blades as each of my propellers, but less than such
area, say about of such area.
2nd. That the lower entering edge F near the boss of the blades of one of my
propellers shall approximately lie in the same longitudinal plane with the lower
rearward edge G near the boss of the blade of the adjacent divided propeller
iooking fore and aft, or equivalently that the centres of two adjacent blades in any
sets of divided 3 blade propellers, are not more than 50° apart looking fore and
aft; and that the blades of one propeller shall not lie in the same spiral path as
the blades of the other, when both sets of blades are situated, as shewn, close
together on the shaft.

page_text: The blades of each propeller may be duplicates of one another, and for maximum
efficiency are preferably so, as regards their shape and area of blade. I have
found an excellent increase of efficiency result from a divided propeller, of which
all the blades are similar to one another, as regards area and pitch, when disposed
relatively to one another as above described upon the propeller shaft, and properly
proportioned as above described as regards the area of all the blades relatively to
the normal area of a blade of a single ordinary propeller.
I may however slightly increase the pitch of that part of the divided propeller
nearest to the rudder and reduce its surface, as regards that part of the propellor
forward of it.
I may also use a number of reinforcing divided propellers one behind another,
upon a shaft regard being always had to the relative dispositions of the blades of
the successive propellers to break interval one with another with approximate
coincidence of the rearward edge of the leading propeller blade to the entering
edge of a successive one as above described, each "breaking spiral" one with
another and the area of each of the blades being reduced relatively to the normal
area of the blade of an ordinary single propeller in the proportion as above
described, but still further reduced in number of propellors employed.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what I
claim is:
1st. A divided propeller having two approximately similar sets of blades upon
the same shaft, the area of each blade being intermediate between that of the
normal blade of a single propeller of the same number of blades as each of
the divided propellers, and one half of such normal area (so that the total area of
the blades is substantially in excess of that of a normal single propeller) and the
lower rearward edge near the boss of each propeller blade towards the rudder
being approximately in the same longitudinal plane with the lower entering edge
near the boss of the forward adjacent propeller blade, looking fore and aft; each
set of propeller blades breaking spiral with those of another set, when close
together on the shaft, substantially as described.
2nd. The combination of more than 2 sets of propellers upon the same shaft,
having the total area of their blades substantially in excess of that in a normal
single propeller, but having the area of the blades of each propeller less than that
of a normal single propeller, such blades being arranged as described in the first
claim substantially as set forth.
Doted thin 92nd day of Tren 1907
FELL & JAMES,
1 Queen Victoria Street, London, E.C., Agents for the Applicant.