IMPROVEMENTS IN SCREW-PROPELLERS
Year: 1884

page_text: I HENRY HARRIS LAKE, of the firm of Haseltine, Lake, and Co, Patent Agents,
Southampton Buildings, London, in the County of Middlesex do hereby declare
the nature of said invention for "IMPROVEMENTS IN SCREW-PROPELLERS" 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 the construction of blades for screw
propellers and has for its object to utilize a portion of the great amount of power
that is lost by the present construction.
The said invention comprises the peculiar construction of the blade, as
hereinafter described.
In the accompanying drawing
Figure 1 is a perspective view of the improved propeller.
Figure 2. is a sectional end view of the same on the line xx Figure 1, and
Figure 8, is a section of one of the blades, obtained by the intersection with a
cylinder and then developed on a plane, showing the improvement.
By sharpening the blade on the after or working edge as illustrated in Figure 3,
and constructing the working face with a convex surface, I obtain useful work,
with less friction and resistance due to the blade, from all the power applied to
the propeller, than has ever before been accomplished.
"
Imagine the blades of a. propeller constructed according to this invention to be
intersected, by a cylinder, the axis of which is co-incident with the centre of the
shaft on which the propeller turns, and let the section of one of the blades to be
developed on a plane, as shown in Figure 3. Through the after edge A of the
blade I draw the line A-B perpendicular to the shaft, or in. the plane of the
propeller's motion. I then draw from the forward edge O the line-plate B-C
parallel with the shaft; I have in B-C the pitch of the propeller corresponding
to the width of one blade. If from the point C I set down the amount of slip
to D and join A-D, I have in A-D what may be called "the line of motion
that is to say by the combined endwise motion of the propeller, every point in the

page_text: section will revolve in a helix, which, when developed on a plane, will be strictly
parallel with the line A-D; and in the line B-D I have the net pitch
corresponding to the width of one blade.
I
It is the negative resistance due to the thickness of the blade that I wish to get
rid of, as this is a very important part of the total work of the wheel.
accomplish this by constructing the forward face of the blade with a convex
surface, or on the curve of a parabola, or are of a circle of large radius, and so
arranged as to be tangential to the line of motion in the forward edge of the blade,
whereby the angle of resistance is at a minimum, as the direct resistance against
the motion of the blade in edge is less, and the component promoting the forward
motion of the vessel is greater as the angle between the line drawn parallel to the
line of motion, and at the same time tangential to the upper convex surface at its
forward edge, and the line drawn tangent to the sharpened after side at a point
midway of the thickness of the blade, is less.
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 :-
A propeller-blade, sharpened on the after side at the forward or leading edge,
and having its forward side constructed with a convex surface so as to make it
tangential to the "line of motion" at the forward edge of the blade, substantially
as, and for the purpose, set forth.
'Doing thin 10th 3.
T
HASELTINE, LAKE & Co.,
For the Applicant.