Improvements in the Shape of the Propelling Surface of the Blades of Propeller Wheels Used in Propelling Vessels through or on the Water
Year: 1888

page_text: Improvements in the Shape of the Propelling Surface of the Blades
of Propeller Wheels Used in Propelling Vessels through or on
the Water
I, JOHN EDMUND TRENOUTH BARTLETT, residing at No 253 West 14th Street
City of New York, in the County and State of New York, one of the United States
of America, Gentleman, 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
-
My invention relates to an improvement in the shape of the propelling surface of
the blades of propeller wheels, used in propelling vessels through or on the water and
the objects of my improvement are, first to control the flow of water driven astern
by the propeller, giving it a direction parallel to the axis of the driving shaft and
opposite to the motion of the vessel, second, to prevent the water being raised by
the centrifugal force generated by the angular velocity of the propeller, third, to
gain length of blade with given diameter and thereby decrease the frictional resistance
to be overcome by the engine in rotating the propeller at a given angular velocity,
this resistance increasing as the square of the distance from the axis of the propeller
and fourth, to eliminate the local surface disturbance and currents caused by the dis
persion of the water in any other form of propeller wheel, and as the flow of water is
parallel to the longitudinal axis of the shaft, the banks are not washed away or the
bottom scoured by this form of propeller in navigating narrow or shallow water-ways,
such as canals
I attain these objects by constructing the propelling surface of the blades of the
propeller (which may have as many blades as the fancy of the designer may desire,
usually from two to four) of the form illustrated in the accompanying drawings, in
which
"
Figure 1, is a plan or top view of the propeller, showing a longitudinal section of
the blade on the right and projected sections at the diameters, d, d', d³, d³, and the
characterizing curve, 2, 0, 2, forming the principal feature of my invention

page_text: Figure 2, is a front elevation of the propeller looking aft
Figure 3, is a cross-section through the propeller shaft and the blade of the common
form of screw propeller, the blade being of such a nature that if it were turned on
its axis (having it the same time a motion of translation equal to the desired pitch) a
true pitch wheel having helicoidal surface precisely analogous to the Archimedes
screw, would be generated
Figure 4, is a similar section through that form of propeller commonly known as
the centripetal propeller, which is formed on an oblique generatrix
Figure, is section of my improved form of propeller blade, and shows that
plane passed through the axis of the propeller-shaft will intersect the blade in
parabolic curve
Similar symbols refer to similar parts throughout the specification and drawing
The base line of abscissae, 1, 0, 1, for determining the curve 2, 0, 2, is assumed to
pass through the center line, 3, 3, of the shaft, midway of the length of the pro-
peller hub, 4, 4 The ordinates, h, h, h³, h³, and so on for as many ordinates
equidistant from each other, as may be necessary to determine the curve to the
required degree of accuracy ire calculated using the variable quantity, d, as one of the
values in the formula, suid variable being equal to twice the distance of the point at
which it may be desired to erect the ordin te from the axis of the propeller, using the
parabolic formula, h, == x, f,
in which formula, h, equals the ordinate, h,—h, h¹—h²,
and so on for the different values of d² The curve, 2, 0, 2, drawn through these
points is a parabola
d
Referring to the drawing If a pline be passed through the axis of the shaft of a
propeller of my construction, intersecting the driving surface of either of its
blades, A. A A A, then will the intersection of said plane and driving surface of the
blades, form a parabolic curve, 2, 0, 2, and the driving surface will be a parabolic
surface generated by the revolution of a semi-parabola, 0, 2, whose vertex 18, 0,
around the longitudinal axis, 0, 3, having at the same time a motion of translation
positive or negative in the direction, 0, 3, equal to the required pitch of the propeller
Referring to figure 5, it will be seen that the curve of the blade therein shown, is a
parabola having its vertex at, 0, its focus at, F The focal distance is represented
by, The lines, 8, 8, indicate the flow of water to the wheel, partaking as it does of
the contour of the run of the ship as is actually- the case in practice After the
particles of water have passed behind the blades the directional force of the wheel
will drive it in one of two directions, viz It will be reflected parallel to the shaft
axis Why? Because water being incompressible it cannot be forced at, F, and as
the reflecting surface must drive it one way or the other, it must follow the lines, d, d
The wheel taking water perpendicularly to its feeding edge will draw from the larger
area facing the wheel and said area being in the same ratio as the square of the length
of the curved directrix is to the square of the actual radius of the wheel, the diameter
of the wheel being the smaller diameter of a frustum of a cone whose elements are
parabolas or what may be called a conic-paraboloid, the water behind the wheel will
be compressed, or more strictly speaking, the air in the water which flows to the pro-
peller is compressed so that the wheel works in solid water, thus correcting any
tendency to race racing being a term used to represent the tendency of propeller
wheels to ship ahead of the water with variable speed owing to the existence of air in
the water, hence a wheel of my construction causes less vibration than the other
forms because it works on solid water
The driving surface of this design of propeller will act on the same principle as
sound and light reflectors constructed on the same principle, hence the water driven
astern must necessarily be driven in a stream parallel to the longitudinal axis of the
propeller shaft Any particle of fluid passing behind the leading edge, A, of the
propeller-blade, will be forced back by the advancing surface of the propeller and
the superposed particles being prevented following or flowing off the blades by the
reflecting surface Before said particles can acquire centrifugal force from contact
with a rotating surface of high velocity it will have been left behind by the advancing

page_text: propeller, having no tendency to raise to the surface it will be reflected parallel to
the axis of the shaft as the least resistance is in the direction of the wake of the
vessel
The increase in length of blades is clearly shown in the right hand blade, figure 1,
and the length gained is the difference in length of the curved line, 0, 2, and the
straight line, 0, 1, or length equal to the distance from the point, h, to the point, he,
and as the frictional horse power required to rotate a propeller is equal to the surface-
pressure multiplied by the squire of the velocity, the velocity will be greater as the
diameter is increased Therefore a wheel of the same blade area can be obtained with
less diameter and equal length of blade, in this construction and will require less power
to rotate it at a given angular velocity than a straight blade of equal length
The propelling surface of propellers of my peculiar construction prevent the water
flowing off radially or tangentially, hence there are no waves on the surfice, caused
by the rotation of the propeller and as the water is but slightly agitated there is no
tendency to wash away banks, or scour the bottom of the water-ways of small sectional
area, and my experiments have always shown a wike of as little commotion as is made
by the passage of a vessel under sul, hence I believe this design of propeller is
particularly adapted to steam navigation on canals
I am aware that many designs of propellers have been made with curved blades of
different forms having names given them from some fancied resemblance they may
have to wings of birds and objects I therefore do not claim curved blades as so
constructed, but
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 18 -
The herein described propeller blades curved in the line of a parabolic generatrix
to form a driving surface consisting of a helicoidal parabolic surface of revolution
and so combined with the propeller shaft, that plane pissed through the axis of the
shaft will intersect the driving surface of each blade in a parabola, substantially as
desembod
100 1
1000
Dated this 12th day of June 1888
JOHN EDMUND TRENOUTH BARTLETT
By Jensen & Son,
77, Chancery Lane, London, WC,
Patent Agents