Improvements in Screw Propellers for Steam and other Vessels.
Year: 1889

page_text: Date of Application, 19th Nov., 1889-Accepted, 11th Jan., 1890
COMPLETE SPECIFICATION.
Improvements in Screw Propellers for Steam and other Vessels.
CHARLES INWOOD "Advance" Works, Stone Street, Gravesend, in the County
of Kent, Engineer, 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 has for its object improvements in screw propellers for steam and
other vessels, namely:-The reduction of slip or difference between the linear advance
of the vessel propelled and that of the screw propeller due to its pitch, and the forma-
tion of the blades in such a manner that they shall be of great strength and rigidity
in combination with lightness; the whole of their surface being effective for propulsion
from root to tip. It has hitherto been the practice to make propeller blades by casting
them, but by ny method of construction they may be produced from sheet metal of
the same guage from root to tip without reducing their rigidity; as I have found in
practice that a propeller blade shaped and fitted on my principles, as hereinafter
described, is at least forty per cent. lighter than the ordinary class of cast propeller for
the same diameter.
I do not limit myself to any kind of metal, in fact cast iron may be used without.
departing from the spirit of my invention, but by preference I use wrought iron, steel,
bronze or other metallic alloy, inasmuch as my improved method of making propeller
blades allows me a larger range of metals to select from without overstepping the
limits of economical production than has hitherto been at the command of
manufacturers.
Now, according to my invention, I produce a metal blade as light as possible con-
sistent with the necessary strength required for its purpose, after the manner of A
Fig. I, which represents the propelling surface of the aforesaid blade in a vertical
plane. To obtain the helicoidal curves for the delineation of screw thread to a given
pitch, I make a block or former on which each half of the blade, through dotted
line, Fig. I, is shaped, which produces an end view of a vertical elevation of the
propeller blade in line with the axis of rotation A Fig. 2. Fig. 3, is a side elevation
of the same blade, whose axial line is at right angles to the major axis of the pro-
peller boss. Fig. 4. is a side elevation of the same class of blade inclined aft, the
formation of which would be produced identically in the same manner as Fig. 3; but,
as a matter of course, one half of the blade would have to be shaped before curving,.
as indicated by the dotted lines c¹ c¹ c¹ c¹, Fig. 1. Fig. 5, is an edge view plan of my
propeller built up with three blades.
It will thus be understood that each propeller blade consists of about the same
amount of propelling surface as an ordinary radial blade, but is so peculiarly shaped
that each complete blade has two roots which spring one from each end of the boss,
and are so arranged that the forward and backward extremities attached to the boss
shall be opposite each other, thus -Each blade joins the boss in two places, the-
forward portion of the blade meeting the forward end of the boss, and the after
portion the other end of the boss, both in a line parallel to each other to a given pitch,
and arranged round each end of the boss equidistant from each other.
Practically the helicoidal radial curves of each complete blade with the propeller
boss form an open triangle which I claim as the chief feature of my invention, since
great strength and inflexibility is obtained by the combination of light metal plates,.
as set forth, and a metal boss for the purpose of a screw propeller. I do not therefore
bind myself to any particular pitch or angle in relation to its diameter, and that the
tip of each blade may be in position over the centre of boss or inclined to same at any
angle to suit the requirements for which my propeller may be designed.

page_text: And I would have it understood that, on taking an end or face view of my pro-
peller, no portion of one blade shall overlap that of another.
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 is :-
1st. The construction of screw propeller blades with helical propelling surfaces, in
combination with the propeller boss forming a figure after the manner of an open
triangle, substantially as described.
2nd. The construction of propeller blades with two roots, each joining opposite ends
of the boss, helically disposed and arranged that no portion shall overlap that of
another in line with the axis of rotation or advance, as hereinbefore described with
reference to the accompanying drawings.
Dated this 16th day of November 1980
CHARLES INWOOD.