AN IMPROVEMENT IN SCREW PROPELLING
Year: 1856

page_text: LETTERS PATENT to Edward Tombs, of Islington, in the County of
Middlesex, for the Invention of "AN IMPROVEMENT IN SCREW PROPELLING."
Sealed the 17th April 1857, and dated the 17th October 1856.
PROVISIONAL SPECIFICATION left by the said Edward Tombs at the
Office of the Commissioners of Patents, with his Petition, on the
17th October 1856.
I, EDWARD TOMBS, of Islington, in the County of Middlesex, do hereby
declare the nature of the said Invention for "AN IMPROVEMENT IN SCREW
PROPELLING," to be as follows:-
My Invention of an improvement in screw propelling consists in altering
the form of the propeller blades, by which increased speed is obtained without
increasing the expenditure of power. In my improved form of propeller the
outer ends of the blades are bent at an angle to the plane of the blade. I do
not confine myself to any specific angle, but prefer the bent part to be at a
right angle to the lower portion. The vessel is fitted with either one or two
of these improved propellers.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Edward Tombs in the Great Seal Patent Office on the
17th April 1857.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EDWARD
TOMBS, of Islington, in the County of Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Seventeenth day of October, in the year of our
Lord One thousand eight hundred and fifty-six, in the twentieth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Edward Tombs, Her special licence that I, the said Edward Tombs, my
exccutors, administrators, and assigns, or such others as I, the said Edward
Tombs, 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 "AN IMPROVEMENT IN SCREW
PROPELLING," upon the condition (amongst others) that I, the said Edward
Tombs, 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 Edward Tombs, 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 the following state-
ment:-
My Invention of an improvement in screw propelling consists in altering
the form of the propeller blades, by which increased speed is obtained with-
out increasing the expenditure of power. In my improved form of propeller
the outer end of the blades are bent at an angle to the plane of the blade.
I do not confine myself to any specific angle, but prefer the bent part to
be at a right angle to the lower portion. The vessel is fitted with either
one, two, or more of these improved propellers. I- have found the use of two
propellers, when worked according to the mode herein-after described, to be
advantageous, and I will proceed to describe my improved plan of using one,
two, or more screws, either of the bent or flanged form, or of any other form.

page_text: The screw shaft and the meehanism connected therewith for working it
remain as they are; but the dead wood of the ship must be extended so as to
admit of the insertion of an additional screw, one being placed before the
other. The two screws are actuated by the one ordinary shaft, and to effect
this a gearing or cog wheel is keyed on to the shaft between the screw and
the stern post or framing. The second or hindmost screw is supported between
this stern post and an additional stern post or framing, the axis or shaft being
fitted at the end nearest the stern, with another gearing or cog wheel taking
into that on the shaft of the second screw. Motion being given by the engine
to the propeller shaft, the first screw with its gearing wheel will revolve,
thereby giving motion to the second gearing wheel, and this wheel carries with
it the axis of the second screw; the two screws revolving in reverse direc-
tions, as must be obviously understood. The two gearing wheels may be of
the same diameter, in which case the two screws will revolve at the same rate,
or nearly so; or the first wheel may be of a larger diameter than the second,
when of course the second wheel will revolve at a faster rate than the first
one, according to well known mechanical principles. I claim to use both
arrangements, although I believe it will be found preferable in practise to use
the wheels of unequal diameters, so as to give a more rapid motion to the
hindmost screw; but up to the present time I have not been able to make
experimental trials on such a scale as to enable me to give a decided pre-
ference. The gearing wheels may be boxed over, or otherwise protected
against sea-weed or other extraneous matter which might impede their action.
I am aware that it.has been proposed before to use two screws, one before the
other; but then they were worked by two shafts, the outer shaft being hollow,
to admit of another working inside to actuate the second screw. This mode,
for various reasons, has not answered in practice; and it has been proposed to
work two screws in parallel positions, in which case there are two sterns and
stern posts, and two sets of gearing; an arrangement which has not come
into general use, if it be used at all. My improved mode of using two screw
propellers has the following advantages:-The present engine and shafting
remain unaltered; the stern of the ship is not materially altered in form. The
"slip" caused by the ordinary screw is saved by the use of the second.
Instead of using two screws with the gearing wheels, I may use one screw,
worked by gearing wheels, which plan will give an advantage over the present
mode of using the screw propeller.
Having now described the nature of my said Invention, I wish it to be
understood that I make no claim to the principle of using two screw pro-

page_text: pellers; but what I clain is the screw propeller herein-before described, and
the using of one, two, or more screw propellers, when worked by one shaft
with gearing wheels, or any mere equivalent therefor.
In witness whereof, I, the said Edward Tombs, have hereunto set my
hand and seal, this Seventeenth day of April, in the year of our Lord
One thousand eight hundred and fifty-seven."
EDWARD TOMBS. (L.S.)