Improvements in Ships Propellers..
Year: 1888

page_text: Improvements in Ships Propellers..
2. :
1, BENJAMIN JOSEPH BARNARD MILLS carrying on business under the firm or
style of Harris and Mills of 23 Southampton Buildings, in the County of Middlesex
Patent Agent do hereby declare the nature of this invention, a communication to me
from abroad by Louis Bidauld of Lyons, in the Republic of France, Engineer, and in
what manner the same is, to be performed, to be particularly described and ascertained
in and by the following statement
-
This new propeller rotates like the ordinary screw in a plane normal to that of the
direction of the ship; it consists of a variable number of blades, the special form of
which constitutes the subject of the present invention.
The accompanying drawing "represents, at Figure 1, a face view of the propeller
and, at Figure 2, an edge view of the same, the front blade being drawn in section on
the line 1, 2, of Figure 1.
The propeller turns in the direction of the arrow and advances consequently from
left to right.
It will be noticed that the two faces, back and front, of the blade are constructed
of two different curves. The rear face A, B, has a concave form, the first element A.
of which nearly follows the direction of the resultant A. R of the speed of the blade
A, x, and of the speed of the boat A, y. The last element B of the same curve
approaches more or less to the direction of the axis of rotation, without actually
following it.
It results from this form that the water will slide more easily from A to B, than
upon a plane surface without causing eddies injurious to the useful effect. The water
can in effect be compared to a body falling from the point A which will arrive
faster at B following a curve than following a right line.
The rear face does not alone act for the propulsion and, whilst it presses upon the
water to advance, the front face creates along the line A. C, a vacuum which draws
it forwards, and cooperates largely in the useful effect.
If the substance of the blade is limited, as heretofore, to a thickness, nearly uniform,
by making the curve A, C, parallel to A, B, the vacuum formed extends beyond the
blade after its passage and becomes filled with eddies which accompany the blade and
neutralize all attraction.

page_text: It is necessary therefore that the curve A, C, be of such a shape as to be followed
closely by the water, in order that attraction may be exercised, without eddies and
without loss. Experience. has shown that this curve should be considerably less
inclined on the axis than the rear curve A, B.
These two curves being thus formed from the point A diverge rapidly and give to
the rear of the blade a considerable thickness which is limited by the right line.B, C
parallel to the line of entrance A, R; the face B, C will therefore have no propulsive
action, but it furnishes a better fulcrum for the water, which sliding upon the two
curved faces, quits the blade at the two points B and C, and thus obviates a part of
the recoil.
The section of the blade presents therefore a triangular curvilinear form, each side
of which is formed specially for the effect to be obtained, 'according to the respective
speeds of the vessel and of the propeller.
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:
:-
:
The special form given to the blade of the new propeller, comprising, 1, A rear
concave face upon which the water slides without shock and without eddies; 2, A
front face, convex and less inclined than the former, thus enabling to be utilized, for.
the propulsion, the attraction of the vacuum formed by the passage of the blade ;
and 3, A rectilinear face without direct effect for the propulsion, but offering a better
fulcrum, for obviating recoil, by causing the water to arrive from each face at two
different points.