IMPROVEMENTS IN SCREW PROPELLERS
Year: 1855

page_text: LETTERS PATENT to Thomas McLow, of Middle Row, Holborn, in the
County of Middlesex, Gentleman, for the Invention of "IMPROVEMENTS IN
SCREW PROPELLERS."
PROVISIONAL SPECIFICATION left by the said Thomas McLow at the
Office of the Commissioners of Patents, with his Petition, on the
28th March 1855.
I, THOMAS M Low, of Middle Row, Holborn, in the County of Middlesex,
Gentleman, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN SCREW PROPELLERS " to be as follows:-
This Invention relates to an improved form and arrangement of the blades
of screw propellers, whereby the water is prevented from spreading out at
right angles or radiating from the propeller shaft by the centrifugal action of
the blades, as is the case with the propellers at present in use. By this pro-
peller nearly all the resisting force of the water is absorbed or taken up
advantageously by the blades which throw it behind the ship in a line with
the keel. The system or mode of setting out the form of the propeller blades
will be readily understood on referring to the annexed sketch, which represents
a Diagram view of a propeller of the improved construction. The face line a
of the blade is drawn from the point c when the vertical centre line 6 intersects
the periphery of the blades, whatever may be the diameter of the propeller.
The length of the spiral, or the distance from d to e, is equal to two-ninths of
the whole diameter of the propeller, and the radius of the curve f, forming the
back line of the blades, is equal to the diameter of the propeller. When two
propellers or double blades are used, or a small power with a large diameter

page_text: of propeller, then the length of blade, or the distance from d to e, will be made
shorter, according to the stroke and power of the engine, and the curve f will
be of a longer radius in proportion as the length of blade is shortened; that is
to say, if the length of blade be one-half of that shewn in the sketch, the
rdius of the curve f will be doubled, and so in proportion, according to a
greater or less length of blade. The faces of the blades are hollowed out to
the extent of one-eighth of an inch to, a foot in. the length of the blades, such
hollowing commencing a short distance from the boss, and terminating a short]
distance from the periphery, according to the length of blades. The double
blades are brought into line with each other when not propelling. The front
propeller will be in the propelling position when the vessel is to be propelled,
& is turned from the propelling position when under sail by the resistance
or pressure of the water, which causes it to take up a position in a line in
front of the back or hind propeller, which is fixed to the propeller shaft.
When the two propellers are in a line with each other, they will be entirely
within the dead wood of the ship. The front propeller is allowed to move in
& out of its position by a long mortise hole in the boss working over a pin
in the shaft. The pitch of the back propeller should be one-tenth greater than
that of the fore or front propeller, and the space between the propellers, if
convenient, should be about half the length of the blades, that is, half the
distance between the points d and e in the sketch. If there is not sufficient
convenient room, however, they may be brought nearer together.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Thomas McLow in the Great Seal Patent Office on the
26th September 1855.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
MeLow, of Middle Row, Holborn, in the County of Middlesex, Gentleman,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-eighth day of March, in the year of our Lord
One thousand eight hundred and fifty-five, in the eighteenth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Thomas M Low, Her special license that I, the said Thomas M°Low, my
executors, administrators, and assigns, or such others as I, the said Thomas
McLow, 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 PRO-
PELLERS," upon the condition (amongst others) that I, the said Thomas M°Low,
by an instrument in writing under my hand and seal, 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 Thomas M°Low, do hereby declare the
nature of the said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement, that is to say :-
This Invention relates to an improved form and arrangement of the blades
of screw propellers, whereby the water is prevented from spreading out at
right angles or radiating from the propeller shaft by the centrifugal action of
the blades, as is the case with the propellers at present in use.
The accompanying Drawings fully illustrate my Invention, in which Fig. 1
is an end elevation or face view of a propeller, shewing the mode of setting
out its form; Fig. 2 is a side view of the same; Fig. 3 is a plan of the same;
Fig. 4 is an end elevation or face view of a double propeller for auxiliary
purposes while stationery; Fig. 5 is a side view of the same; Fig. 6 is a

page_text: plan of the same; Fig. 7 is an end elevation, shewing their position while in
action. Similar letters of reference indicate corresponding parts in the several
Figures.
By this propeller nearly all the resisting surface of the water is absorbed or
taken up advantageously by the blades, which throw it behind the ship in a
line with the keel. The system or mode of setting out the form of the pro-
peller blades will be readily understood on referring to Fig. 1, where it will be
seen that D, E, and E', D', are parts of a circle, the radius of which is at the
centre of the shaft G. The distance from D to E and E¹, D', is equal to
2-9ths of the diameter of the propeller. The vertical centre line B intersects
the periphery of the blades. The face lines A, A¹, are drawn from the points
C, C', to D and D¹ respectively, and the radius of the curves F and F¹, forming
the back lines of the blades, is equal to the diameter of the propeller; the said
back lines or curves to extend from E and E¹ to where the face lines A and A'
intersect the horizontal centre line H, and where the said face lines and curves
intersect the said horizontal line, gives the size of the boss.
the
When two propellers or double blades are used, or a small power with a
large diameter of propeller, then the length of the blade, or the distance from
D to E, will be made shorter, according to the stroke and power of the engine,
and the curves F and F will be of a longer radius in proportion as the length
of the blade from D to E is shortened; (that is to say) if the length of the
blade be one-half of that shewn in Fig. 1, the radius of the curves will be
doubled. The double propellers are fully shewn in Figs. 4, 5, 6, and 7. The
above double propeller is applicable to auxiliary steam vessels, in which a
means is provided for making the blades take up a diminished space laterally
when the vessel is being propelled by wind alone, so as to offer a less amount
of opposing surface to the passing water. The propeller L is keyed upon
shaft whilst the other is loose, and is prevented in any convenient manner
from moving longitudinally upon the shaft. The boss of the fixed propeller has
segmental grooves cut on the face adjacent to the boss of the loose propeller
J, which has segmental projections M working in the said grooves. This
arrangement, which may be modified in various, limits the movement of
the loose propeller J on the shaft in such manner that when the segmental
projections M are each at one end of their said grooves, the propellers will
then be in their propelling position, see Fig. 7, and when the segments are
each at the other end of their grooves the two propellers will be in a line,
see Fig. 4, so as to lie within the dead wood of most vessels made of timber.
When the vessel is being propelled ahead, the propeller J is turned into the

page_text: propelling position by the resisting pressure of the water, and when the vessel
passes through the water with the propellers not revolving, the water will act
on the back of the loose propeller J, and cause it to take up a position in a
line with the fixed propeller, when they will offer considerably less resistance
to the motion of the vessel through the water; care, however, must be taken
that the propellers are placed for such purpose in an upright position, which
may be done by having the engines stopped at a certain position. The loose
propeller J is to move so far that the face line A at the top of its blade will
be at right angles with the face of the fixed propeller L, which will be the
leading one, and of one-tenth more pitch than the loose propeller. The
distance between the propellers should be about one-half the length of the
blade, that is, half the distance between the points D and E. This, however,
may be. regulated according to convenience. A band may be fixed on the
propeller L, covering the projections M and their grooves, so as to ensure their
perfect action. The faces of these blades to be hollowed out in the following
manner, that is to say, a straight. edge is placed across the face of the pro-
peller at an angle of twenty degrees with the vertical line B; the face of the
propeller at that angle must be perfectly flat. The said straight edge, which
is represented by a thick line in Fig. 1, is drawn at that angle from the boss
to the periphery of the propeller; and if the face be flat at that angle, it will
shew, when the straight edge is placed at right angles to the vertical line
across the face of the blade, a hollow in the face of the blades of about one-
eighth of an inch to a foot, according to the length of the blade.
Some vessels built of iron have a very fine run at the stern post, and it will
be found necessary to make the boss smaller. This is accomplished by bringing
the point C lower down the vertical line B as much as may be required, so
that the face lines A and A¹ may be drawn to the boss in a similar manner as
that shewn and described, and to give the lines F and F¹ a little more curve
in proportion, as well as making the length of the blade from D to E and
E' to D' one-fourth (if required) of the diameter, or such length according
as the boss is reduced.
Having thus fully described the particulars and nature of my Invention,
and in what manner the same is to be performed, I wish it to be understood
that as the slightest deviation in forming my propellers would approach the
effect produced by and include the principle of my Invention, though not
arrive at the perfect point I herein describe,, I do not confine myself to
proportioning the propeller to the exact lines and sizes, as before mentioned;
but what I do claim is,-

page_text: First, the application of the principle of setting out the form of a propeller
as shewn in Fig. 1, as well as when the boss is made smaller.
Second, hollowing the faces of the blades in the manner-set forth.
And, third, applying the above principle to do:ible propellers for auxiliary
purposes, and in such a manner that the fixed propeller L when in motion
is the leading one, and substantially as herein described.
In witness whereof, I, the said Thomas McLow, have hereunto set my
hand and seal, this Twenty-sixth day of September, in the year of our
Lord One thousand eight hundred and fifty-five.
THOMAS MCLOW. (L.S.)