Improvements in Screw Propellers.
Year: 1892

page_text: Dte of Application, 9th July, 1892
Complete Specification Left, 18th Mar., 1893-Accepted, 6th May, 1893
PROVISIONAL SPECIFICATION.
Improvements in Screw Propellers.
JOHN HARPER, 169 Park Road, Dingle, Liverpool, Joiner, do hereby declare
the nature of this invention to be as follows:-
This invention is designed mainly for the purpose of obtaining a screw propeller
having blades not easily broken off and one that shall give much less strain to the
shaft than those at present in use.
My blades are two in number and are attached to the boss which may be made
of various shapes and spring from more than a third to even a half or more of the
circumference of the boss each. They may if desired be removably fastened to
the boss by means of screwing or otherwise, so that one can be removed for repair
or renewal without condemning the whole propeller.
"
The blades are nearly circular by preference, the circle enclosing a large part of
the boss. By this means, the greatest width of screw is close to the boss. The
end gradually tapers off in circular arc so that the "corners are not liable to
break off and the strain on the blade is less. The blades almost enveloping the
boss though thin, have such a complete and prolonged union to it that they cannot
well be broken off.
Sometimes I may form the end of the blade by a circle coinciding with the circle
of rotation of the outermost extremity or of larger diameter than that of the
remainder of the blade. The blade can be flat or twisted in the usual manner.
For most purposes the pitch of the screw divided by the radius at that point from
the centre of the boss should be approximately constant. That portion of the boss
nearest the propelling side of the blade may be made smaller in circumference
thereby increasing the blade surface without in any way impairing the strength or
efficiency of the propeller.
One great advantage of this propeller is that the blades being practically con-
centric, in the event of one being injured or broken off, there is still a useful and
efficient propeller remaining.
There is also less splashing and side resistance with this propeller.
DL
TLT
11 11
COMPLETE SPECIFICATION.
Improvements in Screw Propellers.
I, JOHN HARPER, of 169, Park Road, Liverpool, in the County of Lancaster,
Joiner, 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 is designed mainly for the purpose of obtaining a screw propeller
which shall be efficient, and in which the blades shall not be easily broken off, and
one that shall give much less strain to the shaft than those at present in use.
My blades are two in number, and are attached to the boss (which may be
made of various shapes); and they spring from say more than a third or half, or
even preferably more, up to an entire encircling of the circumference of the boss.
They may, if desired, be removably fastened to the boss, by means of screwing
or otherwise, so that one can be removed for repair or renewal without condemning
the whole propeller.
The blades are in some cases nearly circular, the circle enclosing a large

page_text: part or the whole of the boss. By this means a great width of screw is close
to the boss. The ends or tips of the blades gradually taper off in a circular
arc, so that the corners are not liable to break off, and the strain on the
blade is less. The blades, almost or wholly enveloping the boss, though thin,
have such a complete and prolonged union with it, that they cannot well be
broken off.
Sometimes I may form the tips or ends of the blades of a curve coinciding with
the circle of rotation of the outermost extremity of said blades, or of a curve
having a larger radius than that of the remainder of the blades. The blade can
be flat or twisted in the usual manner.
That portion of the boss nearest the propelling side of the blade may in some
cases be made smaller in circumference, thereby increasing the blade surface
without in any way impairing the strength or efficiency of the propeller.
There is with this propeller less splashing and side resistance than with ordinary
propellers.
In the drawings hereto annexed, I shew an example of my two bladed propeller
embodying the improvements the nature of which is above described; it is to be
understood at the same time, however, that the characteristic or essential feature
of the invention therein illustrated may be applied to screws having other forms of
blades.
In the drawings, a is the boss of the propeller which, as will be seen, is of
spherical form, and b is the portion of each blade which is carried past the centre,
of the boss to about a point coincident with the radial centre line, which passes
through the blades, where it merges into the boss. It is this portion of the blade
which effects the main improvement and ends above specified, that is to say,
by this feature the boss, whether of spherical or other known form, revolves
about its axis with neutral effect, but the blades act with propelling effect both at
the centre as well as the parts outside the boss; or, in other words, the whole area
of the propeller within a circle passing through the extremities of the blades, is
effective as regards propelling effect.
The two blades, as will be seen, are of circular form (which is represented by
the dotted circles c); but as above stated they may be of any suitable form.
The centre of the blades in the example shewn are designated x, and they are so
disposed or arranged that the inner part of the circles enscribing the blades, are
tangential to the circle of the boss, a, thus the parts b encircle it. This form, as
above stated, also affords great strength, in that the blade centres are near the
boss, and the tips taper off in a circular arc, so that the ends are not so liable to
break off, and less strain is put upon this part, and the shaft, in work. Besides
this, the blades wholly encircling the boss by the parts b provide a very secure or
firm connection of the blades with the boss.
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is:-
:-
A screw propeller having two blades with parts near the boss carried round or
about same; substantially as herein set forth for the purposes specified.
Dated this 17th day of March 1892
CHEESBROUGH & ROYSTON, Fels. Chart. Inst. P.A.,
15, Water Street, Liverpool, Applicant's Patent Agents.