IMPROVED SCREW PROPELLERS
Year: 1885

page_text: FREDERICK FRIEDENTHAL Naval Engineer of 18 Chapel Walks Preston in the
County of Lancaster do hereby declare the nature of my invention for IMPROVED
SCREW PROPELLERS to be as follows :-
--
The object of this invention is to improve Screw Propellers by special design of
blade of such a shape. so as to give the best result with least resistance and to use
such curves that the said blades can also be strickled out in loam without the
necesity of making patterns.
To gain this object I design the blades as follows:
I first divide the length of blade in five equal parts from centre of shaft and
mark the divisions No 1, 2, 3, 4 and 5; then I mark the width of blade on N° 1
division and strike a circle with radius equal to half the diameter of propeller from
point A, through A in line with division N° 1, thus forming the leading edge of
blade & strike a circle with same radius from point B, through B thus forming
the trailing edge of blade.
Having thus formed the outside shape of blade with two semicircles & stright
line on top with corners rounded off, I next proceed & divide the width of blade on
N° 1 division into four equal parts & strike circles with radius equal to half
diameter of screw plus one fourth the width of blade the said circles intersecting
the first & third division on drawing marked E and H, the centre of this circles to
be as before on N° 1 division.
I consider the area enclosed in E F G H the main area of blade & make same
true thread from boss to tip.
In the area enclosed in A C F E I reduce the pitch from tip of blade to boss
gradually by two per cent or thereabouts for each division so that at the division
No 5 the pitch of the main area will be reduced by two per cent, at N° 4 division
by four per cent and so forth till I reach N° 1 division when the pitch will be
reduced by ten per cent or thereabouts.
On the contrary side that is in the area enclosed by HGDBI increase the
pitch from the boss to tip by five per cent or thereabouts for each division so
that the pitch at N° 1 division will be pitch plus five per cent, at N° 2 pitch plus
ten per cent & so forth till I reach N° 5 division where the pitch will be pitch
plus twenty five per cent or thereabouts.

page_text: ( I FREDERICK FRIEDENTHAL, of 18 Chapel Walks, Preston, Lancashire consulting
Engineer do hereby declare the nature of my invention for IMPROVED SCREW'
PROPELLERS and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
The object of this invention is to improve screw propellers by special design of
blades of such a shape and pitches so as to give the best result with least power
expanded and to use such curves that the propeller can also be strickled out in
loam without the necesity of making costly patterns.
To gain this object I design the blades as follow:
To draw the blade I first divide the length of blade in five equal parts from
centre of shaft and mark the divisions N° 1, 2, 3, 4 & 5-then I mark the width
of blade on N° 1 division and strike a circle with radius equal to half diameter of
propeller from point A₁ through A in line with division N° 1 thus forming the
leading edge of blade & strike a circle with same radius from point B₁ through B
thus forming the trailing edge of blade.
Having thus formed the outside shape of blade with two semicircles & stright
line on top with corners rounded off I next proceed & divide the width of blade on
N° 1 division in four equal parts & strike circles with radius equal to half diameter
of screw plus one fourth the width of blade the said circles intersecting the first &
third division on drawing marked E & H, the centre of this circles to be as before
on No 1 division.
I consider the area enclosed in E F G H the main area of blade & make same
true pitch from base to tip.
In the area enclosed in A C F E I reduce the pitch from tip of blade to boss
gradually by two per cent or thereabouts for each division so that at the division
N° 5 the pitch of the main area will be reduced by two per cent, at N° 4 division
by four per cent and so forth till I reach N° 1 division when the pitch will be
reduced by ten per cent or thereabouts..
On the contrary side that is in the area enclosed by H G D B I increase the
pitch from the boss to tip by five per cent or thereabouts for each division so that
the pitch on N° 1 division will be pitch plus five per cent on N° 2 pitch plus ten per
cent & so forth till I reach N° 5 division where the pitch will be pitch plus twenty
five per cent or thereabouts.
I prefer semicircles for the outline of blades on account the ease with which same
can be drawn & tested but it is obvious that if the construction of sternpost do
not allow overhanging blades, the radius of circles can be made larger than above
discribed.

page_text: This propellers can be made of any suitable metal with any desired number of
blades either solid or portable.
Having now particularly described & ascertained the nature of my said
Invention, and in what manner the same is to be performed I declare that what
I consider to be novel & desire to protect by letters Patent is 1
1. Propellers designed & constructed substantialy as, and for the purposes, herein
before described.