IMPROVE- MENTS IN SCREW PROPELLERS
Year: 1868

page_text: LETTERS PATENT to James Sinclair, of Stirling, in the County of
Stirling, North Britain, Engineer, for the Invention of "IMPROVE-
MENTS IN SCREW PROPELLERS."
Sealed the 25th September 1868, and dated the 31st March 1868.
PROVISIONAL SPECIFICATION left by the said James Sinclair at
the Office of the Commissioners of Patents, with his Petition, on
the 31st March 1868.
I, JAMES SINCLAIR, of Stirling, in the County of Stirling, North
Britain, Engineer, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN SCREW PROPELLERS," to be as follows, that is to
say :-
This Invention relates to the application in the construction of
screw propellers of an improved configuration combined with certain
proportions whereby an increased propelling effect may be obtained;.
and it consists in shaping each blade with a varying pitch or inclination
which increases from the forward edge towards the middle, and decreases
from the middle to the after edge. This configuration admits of a

page_text: greater average pitch, and of a larger area than ordinary being
advantageously used; and it is preferred in carrying out the Invention
to adopt these increased proportions. A. screw propeller made in the
manner indicated and experimentally tested has been found to give
an increased speed with fewer revolutions of the engine, and to
produce considerably less tremor of the stern of the vessel than a screw
propeller of the ordinary kind.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said James Sinclair in the Great Seal Patent Office
on the 29th September 1868.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JAMES
SINCLAIR, of Stirling, in the County of Stirling, North Britain,
Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Thirty-first day of March, in the
year of our Lord One thousand eight hundred and sixty-eight, in the
thirty-first year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said James Sinclair, Her special licence,
that I, the said James Sinclair, my executors, administrators, and
assigns, or such others as I, the said James -Sinclair, my executors,
administrators, and assigns, should at any time agree with, and no others,
from time to time, and at all times thereafter during the term therein
expressed, should and lawfully might make, use, 'exercise, and vend,
within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "INPROVEMENTS. IN SCREW
PROFELLERS," upon, the condition (amongst others) that I, the said James
Sinclair, my executors or administrators, by an instrument in writing
under my, or their, or one of their hands and seals, should particularly
describe and ascertain the nature of the said Invention, and in what
manner the same was to be performed, and cause the same to be filed
in the Great Seal Patent Office within six calendar months next and
immediately after the date of the said Letters Patent..
L
NOW KNOW YE, that I, the said James Sinclair, do hereby declare
the nature of my said Invention, and in what manner the same is

page_text: to be performed; to be particularly described and ascertained in and
by the following statement in writing, reference being had to the
accompanying Drawings, that is to say:-
My said Invention relates to the application in the construction of
screw propellers of an improved configuration combined with certain
proportions, whereby an increased propelling effect may be obtained;"
and it consists, in shaping, cach blade with a varying pitch or inclination
which increases from the forward edge towards the middle, and
decreases from the middle to the after edge. This configuration admits.
of. a greater average pitch and of a larger arca or size of blade, than
ordinary being advantageously used; and I prefer in carrying out my
Invention to adopt these proportions.
And in order that my said Invention and the manner of performing
the same may be properly understood I have hereunto appended a
Sheet of explanatory Drawings to be herein-after referred to, and
representing a two-bladed screw propeller as constructed according to
my Invention:
Figure 1, is a plan and Figure 2 is a stern end elevation showing
the surfaces which propel ahead.
My improved configuration may of course be applied to propellers
with more than two blades, and it will, in fact in general, be most
convenient to adopt more than two blades in order that a large
aggregate area of the blades may be obtained without occupying too
large a space.
.
In designing the screw shown in the Drawing, which is one of
twelve feet in diameter, delineated on a scale of half an inch to. the
foot, the blade, as seen in Figure 2, is divided into four portions by
radial lines shown in red; then the pitches for the middle part and.
for the fore and after parts being 'determined arbitrarily, and being in
this example 32 feet 4 inches and 19 feet 5 inches' respectively, which
may be termed the "propelling" and "nett" pitches, the first or
leading part 1 is made of the said nett pitch at the edge, and for a
greater or less distance therefrom; the two middle parts 2, 3, are
made of the said propelling pitch from the middle to a greater or less
distance on each side; and the after part 4 is made of the said nett
pitch from the after edge to a greater or less distance therefrom. The

page_text: pitch may vary or change more or less abruptly or gradually, but I
prefer it to change gradually.
My present Invention does not relate to any variation of pitch along
any radial line from the centre to the circumference, but such variation
may be combined with my improvements if wished, or the pitch along
any radial line may be uniform as in ordinary screws.
The intention of my improved configuration is that the pitches of
the fore and after parts 1, 4, of the blade shall approximate to what
may be termed the nett pitch of an ordinary screw of uniform pitch,"
that is, the pitch of the blade less the per-centage of slip (such slip
being estimated relatively to the water in which the screw actually
works). These parts will then tend to move through the water edge-
ways, and would not by themselves exert any pressure on the water.
The middle or propelling parts 2, 3, being of a greater pitch exert a
pressure on the water on the after or propelling side (and could in
fact produce no propelling effect without such pressure), whilst they:
tend to produce a void on the fore side. In a common propeller of
uniform pitch this pressure is produced over the entire surface, and the
water so pressed tends to spread, and part of it finds its way round
the fore and after edges to the void on the fore or non-propelling side
of the blade, and thereby involves loss of effect. In my improved
propeller, however, the passage of the water round the edges is as it
were obstructed by the nett pitch parts 1 and 4, and the tendency of
the water to pass round is as it were converted into a pressure on
those parts of the blade, which pressure is obviously useful. In-
dependently of these considerations it is obviously an advantage for
the fore and after edges to pass through the water edgeways or as
nearly so as possible.
A screw propeller made with my herein-before described improve-
ments, and experimentally tested in comparison with a common screw
has been found to give an increased speed with fewer revolutions of
the engine, and to produce considerably less tremor of the stern of
the vessel than a screw propeller of the ordinary kind.
Having thus particularly described my said Invention, and the manner
in which the same is to be performed, I have to state that I do not
restrict myself to the precise details herein described or delineated,
but that what I believe to be novel and original, and claim as the

page_text: Invention secured to me by the herein-before in part recited Letters'
Patent is, the shaping of the blade of a screw propeller with lesser
pitches at and near the fore and after edges than at the middle sub-
stantially as herein-before described.
.In witness whereof, I, the said James Sinclair, have hereunto
set my hand and seal, this Twenty-eighth day of September,
in the year of our Lord One thousand eight hundred and sixty-
eight.
Witness,
EDMUND HUNT,
Patent Agent,
Glasgow.
JAMES SINCLAIR. (L.s.)