IMPROVE- MENTS IN SCREW PROPELLERS
Year: 1870

page_text: LETTERS PATENT to William Sketchley, of the New Bridge Inn,
Commercial Road, in the Parish of Melcombe Regis, in the County
of Dorset, Wood Cutting Engineer, for the Invention of "IMPROVE-
MENTS IN SCREW PROPELLERS."
PROVISIONAL SPECIFICATION left by the said William Sketchley at
the Office of the Commissioners of Patents, with his Petition, on
the 30th April 1870.
I, WILLIAM SKETCHLEY, of the New Bridge Inn, Commercial Road,
in the Parish of Melcombe Regis, in the County of Dorset, Wood Cutting
Engineer, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN SCREW PROPELLERS," to be as follows:-
That the said screw propeller is of an
screw being fixed at an angle to suit the
"
-
auger" form, the blade of the
speed of any marine engine or
any other power. This is accomplished by elevating or depressing the
blade of the screw which delivers the waste water in an opposite

page_text: direction to the course of the boat or vessel so propelled, and in addition
to accelerating the speed obviates the vibration of the said boat or vessel.
The propeller is also much lighter than those now in use, can be manu-
factured of any metal, and the edge of the blade is perfectly sharp, so
very essential against fouling. An ordinary six-oared boat fitted with 5
ordinary cog gear & winch was propelled by one man the space of
thirty yards in thirty seconds of time, the weight of the screw propeller
being 2 lbs. only.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said William Sketchley in the Great Seal Patent Offico :
on the 29th October 1870.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
SKETCHLEY, of the Now Bridge Inn, Commercial Road, in the Parish of
Melcombe Regis, in the County of Dorset, Wood Cutting Engineer,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Thirtieth day of April, in the year of
our Lori One thousand eight hundred and seventy, in the thirty-third
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said William Sketchley, Her special licence that I, the
said William Sketchley, my executors, administrators, and assigns, or such
others as I, the said William Sketchley, my exccutors, 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 "IMPROVING THE METHOD OF PROPELLING BOATS
AND (OR) VESSELS BY MANUAL OR OTHER POWER OR POWERS BY SCREW PROPULSION,”
upon the condition (amongst others) that I, the said William Sketchley,
my executors or administrators, by an instrument in writing under my,
or their, or one of their hands and scals, should particularly describe and
ascertain the nature of the said Invention, and in what manner the
saine 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.

page_text: NOW KNOW YE, that I, the said William Sketchley, do hereby declare
the nature of my said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by tho
following statement:-
This Invention relates to the production of a new or improved screw
known as a "ship propeller," with a continuous curved blade somewhat
similar in general form to a screw auger, having an amount and
chracter of curve calculated to secure the greatest propelling power
required for different kinds of vessels. The blade is fixed to a hollow
shaft or tube at a varying pitch, to suit the speeds of different engines.
The objects of my Invention are, firstly, to propel vessels at greater
speeds than is now done with the same power of engine; secondly, to
obtain a direct propulsion power without putting the vessel "down by
the stern," as is done by the ordinary screws now in use; thirdly, to
prevent the tremor or vibration to which vessels propelled by screws are
generally subject; fourthly, to attain these objects by means of screws
much lighter and comparatively stronger than those in general use, and
at the same time so simple in construction that they can be made by an
ordinary working mechanical engineer.
The principal means by which these objects are accomplished are in
the general form and pitch of the blade, and in its being a continuous
curved blade, making about one complete turn round its axis. The
contour line or outline of the screw in section is that of a reverse ogec,
the pitch thereof being regulated by elevating or depressing it to what-
ever speed may be determined on for new vessels, and when applied to
old vessels according to the speed of their engines. A further advantage
of this ogce form of the blade is that it gives the screw an equal
power when its motion is reversed as when in direct action. The
improved screw when in motion obtains a perfect grip of the whole of
the water compassed by the blade, and steadily forces the water in the
line of the ship's wake, thereby avoiding any loss of effect from beating
the water into foam or in throwing it in a lateral direction, as is
usually the case, thus preventing any retarding effect on the vessel by
the usual production of adverse currents, etc., and therefore effecting
the propulsion of the vessel to the fullest extent of the power employed.
The steadiness with which my improved screw delivers the water it
engages prevents the injurious jarring and unpleasant vibration so much
complained of in vessels propelled by ordinary screws. Another ad-

page_text: vantage of my improved screw is that it does not require a cylindrical
casing, as is the case with some other screws, this being rendered
unnecessary by the sectional curve or curves of the blade. By making
the blade wedge-shaped or tapering from its base to its outer edge I
obtain considerable strength of blade with a less weight of metal, and t
consequently a light and efficient screw.
The improved screw can be made of any suitable metal, wrought or
cast, I give the preference to steel (if made of any other metal the
outer edge should be of steel), the said outer edge being made perfectly
sharp to prevent the screw choking either with weeds or nets by cutting 1
its way through any such obstructions.
The improved screw may be fixed on the driving shaft in the ordinary
way, the shaft being arranged similarly to those now in use; but if the
vessel be one of considerable tonnage, or requires great power to propel
her, then the shaft should be made to work in a suitable bearing fixed in 1
what is called the false or counter steru post, as shewn in the Drawing,
Fig. 1.
My improved screw can be applied to old vessels by simply removing
the false or counter stern post further back, or by cutting away the
vessel's "stern post" and fixing another further forward, so as to admit
an improved screw of sufficient length to properly propel the vessel. In
the case of "twin screws" at present in use, my improved screw can be
applied without any alteration of the vessel whatever, and will lic more
snugly by the ship's side, and consequently occupy less space and not be
so liable to damage or break down.
In the event of a vessel propelled by my improved screw being by any
means unable to supply the motive power thereto, the screw can be set
free to turn round or not, its form almast entirely preventing it causing
obstruction to the vessel's progress.
DESCRIPTION OF THE DRAWING.
Fig. 1. is an elevation of the screw as fixed to the stern of the vessel,
and Fig. 2 is a section of the blade shewing its sectional outline or

page_text: When the engine is to have a speed of 200 revolutions per minute then
the pitch line of the blade becomes e, g, instead of e, f, Fig. 2, and so on
in proportion for other greater or less speeds.
Having now described and ascertained the nature of my said Invention,
and the means by which the same is to be carried into effect in practice,
I hereby declare that what I claim as my Invention, and desire to secure.
by the before-mentioned in part recited Letters Patent is, the use of
a curved continuous blade of varying pitch, as herein described; and
I would have it understood that I do not claim as my Invention a
continuous blade per se, that is, without the curve, nor the means of
attaching the screw to the driving shaft.
In witness whereof, I, the said William Sketchley, have hereunto
set my hand and seal, this Twenty-eighth day of October, in the
year of our Lord One thousand eight hundred and seventy.
WILLIAM SKETCHLEY. (L.S.)