IMPROVEMENTS IN SCREW PROPELLERS
Year: 1871

page_text: LETTERS PATENT to Charles Denton Abel, of No. 20, Southampton
-
Buildings, Chancery Lane, in the County of Middlesex, Patent
Agent, for the Invention of "IMPROVEMENTS IN SCREW PROPELLERS."
A communication from abroad by Adolphe Aubert, of Rue du
Chateau, No. 22, Neuilly, France, Civil Engineer.
Sealed the 1st March 1872, and dated the 14th September 1871.
PROVISIONAL SPECIFICATION left by the said Charles Denton Abel
at the Office of the Commissioners of Patents, with his Petition,
on the 14th September 1871.
I, CHARLES DENTON ABEL, of No. 20, Southampton. Buildings,
5 Chancery Lane, in the County of Middlesex, Patent Agent, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN SCREW
PROPELLERS," to be as follows:-
'
This Invention has reference to an improved construction of that
description of screw propellers in which the screw is surrounded by, a
O cylindrical casing which revolves therewith.

page_text: This variation of the generatrix, according to an irregular progression
in both its movements, in order to form a blade surface appropriate for
inclosure in a cylindrical casing, forms the essential feature of the
present Invention.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Charles Denton Abel in the Great Seal Patent
Office on the 13th March 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, CHARLES
DENTON ABEL, of No. 20, Southampton Buildings, Chancery Lane, in
the County of Middlesex, Patent Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fourteenth day of September, in the
year of our Lord One thousand eight hundred and seventy-one, in the
thirty-fifth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Charles Denton Abel, Her special
licence, that I, the said Charles Denton Abel, my executors, adminis-
trators, and assigns, or such others as I, the said Charles Denton
Abel, 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
"IMPROVEMENTS IN SCREW PROPELLERS," a communication to me from
abroad by Adolphe Aubert, of Rue du Chateau, No. 22, Neuilly,
France, Civil Engineer, upon the condition (amongst others) that I,
the said Charles Denton Abel, 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.
NOW KNOW YE, that I, the said Charles Denton Abel, do hereby.
declare the nature of the said Invention and in what

page_text: same is to be performed, to be particularly described and ascertained
in and by the following statement thereof, reference being had to the
accompanying Sheet of Drawings, and to the figures and letters marked
thercon, that is to say :-
This Invention has reference to an improved construction of that
description of screw propellers in which the screw is surrounded by a
cylindrical casing.which revolves therewith.
The present Invention has for its object so to construct the screw
blades of such propellers that they shall fulfil the following conditions:-
:―
Firstly. To exert simultaneously upon the whole section of the 1
resisting column of water from the centre to the circumference a
uniform thrust giving an initial velocity of propulsion which, shall be
equal at every point of this surface.
Secondly. To establish a constant force of inertia and an absolute
solidity in all parts of the mass of water submitted to the action of the 1
propeller, in order that the intensity of such action shall always be
perfect and instantaneous whatever may be the condition of the water
upon which the propeller acts, or the sudden operations for manoeuvering
which it is called upon to perform.
For these purposes the geometrical surface of the blades of the 2
improved propeller is not generated according to the principles usually
employed, but are determined by two new principles.
Firstly. The rotation of the generatrix in horizontal projection does
not take place round the centre of the boss but round an excentric
point, so that the directrix upon the boss is of a much greater pitch than 2
the directrix at the junction of the circumference of the blade with the
enclosing cylinder, the generatrix being made to change from a direction
tangential to the boss at the front end of the 'blade into a radial direction
at the back end, and to extend along the boss in plan to about the same
lineal length as at the circumference.
3
Secondly. The generatrix is in vertical projection not perpendicular
to the boss nor inclined at a constant angle thereto, but follows a
variable angle from the front to the back of the propeller. The
cylindrical casing is thus shorter than the width of the blades, and this
difference of length regulates the obliquity of the blades in front, which a
obliquity diminishes from front to back, where it vanishes, the generatrix

page_text: blade at the circumference of the cylinder and of the boss respectively.
As the line A3, B2, in Fig. 5 represent the developed directrix of the
helix at the circumference of the cylinder, so the line a², 62, in Fig. 5
represents the developed directrix at the circumference of the boss, as
determined by the projection above described. The change in the form
of the directrix as it approaches the axis of the screw resulting from
directing the lines of division A, a, C, c, &c., in Fig. 4, not to the
centre o, but to the excentric point p, and from dividing the pitch in
Fig. 3 by the lines A¹, a¹, C¹, c¹, &c., which are not perpendicular to
the axis, but which join points of equal division in the depth of the
cylinder and in the depth of the boss. Thus is produced the quasi-
helical form of blade which forms the subject of the present Invention,
and two, three, four, or any convenient number of such blades may be
employed in a propeller.
Having thus described the nature of this Invention, and in what
manner it is to be performed, as communicated to me by my foreign
correspondent, I claim, the use of a propeller having a cylindrical
envelope in which the blade surface is produced by a varying directrix
substantially as herein described.