IMPROVEMENTS IN VESSELS PROPELLED BY SCREW OR OTHER SIMILAR PROPELLERS
Year: 1857

page_text: LETTERS PATENT to William Macnab, of Greenock; for the Invention
of "IMPROVEMENTS IN VESSELS PROPELLED BY SCREW OR OTHER SIMILAR
PROPELLERS."
Sealed the 16th March 1858, and dated the 6th November 1857.
PROVISIONAL SPECIFICATION left by the said William Macnab; at the
Office of the Commissioners of Patents, with his Petition, on the 6th
November 1857.
I, WILLIAM MACNAB, of Greenock, do hereby declare the nature of the
Invention for "IMPROVEMENTS IN VESSELS PROPELLED BY SCREW OR OTHER SIMILAR
PROPELLERS," to be as follows:-
This Invention has for its object improvements in vessels propelled by
screw or other similar propellers, so as to render such vessels more suitable
for use in shallow water.
For this purpose the vessel is fitted to receive two propellers mounted on
two shafts laid parallel to each other, and these propellers may be of such a
size as either to be totally submerged or only partially so, as may be preferred.
In order to adapt the vessel to receive these propellers in such a way that
they may be protected from injury from floating bodies or otherwise, it is con-
structed with two stern posts, and it is between these two stern posts that the
propellers are placed. In order that the water may not be obstructed, in its
passage to the propellers, the vessel is arranged so as to draw less water at the

page_text: stern than elsewhere; but the stern posts descend to the full draft of the
vessel, in order that the rudders (of which there are two, one on each stern
post), may have sufficient power.
In constructing large vessels, but which are to have a small draft of water,
I sometimes form them with three stern posts, one at the centre line of the
vessel, and another on each side of this central post; in this case I may employ
four propellers, two in each of the openings between the stern posts.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said William Macnab in the Great Seal Patent Office on
the 6th May 1858.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
MACNAB, of Greenock, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Sixth day of November, in the year of our Lord
One thousand eight hundred and fifty-seven, in the twenty-first year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said William Macnab, Her special licence that I, the said William
Macnab, my executors, administrators, and assigns, or such others as I, the
said William Macnab, my executors, administrators, and assigns, should at
any time agree with, and no others, from time to time and at all times. there-
after during the term therein expressed, should and lawfully might make,
use, exercise, and verid, within the United Kingdom of Great Britain and
Ireland, the Channel Islands, and Isle of Man, an Invention for "IMPROVE-
MENTS IN VESSELS PROPELLED BY SCREW OR OTHER SIMILAR PROPELLERS," upon
the condition (amongst others) that I, the said William Macnab, 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 William Macnab do hereby declare
the nature of the 'said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by the
following statement thereof, that is to say :-
This Invention has for its object improvements in vessels propelled by screw

page_text: or other similar propellers, so as to render such vessels more suitable for use in
shallow water.
For this purpose the vessel is fitted to receive two propellers, mounted on
two shafts laid parallel to each other, and these propellers may be of such a
size as either to be totally submerged or only partially so, as may be preferred.
In order to adapt the vessel to receive these propellers in such a way that
they may be protected from injury from floating bodies or otherwise, it is
constructed with two stern posts, and it is between these two stern posts that
the propellers are placed. In order that the water may not be obstructed
in its passage to the propellers, the vessel is arranged so as to draw less water
at the stern than elsewhere; but the stern posts descend to the full draft of
the vessel, in order that the rudders (of which there are two, one on each stern
post) may have sufficient power.
In constructing large vessels, but which are to have a small draft of water,
I sometimes form them with three stern posts, one at the centre line of the
vessel, and another on each side of this central post; in this case I may
employ four propellers, two in each of the openings between the stern posts.
Having thus stated the nature of my said Invention, I will proceed more
fully to describe the manner of performing the same by reference to the

page_text: construction, when two propellers are to be used in the spaces between the
central and outer stern posts. When using three stern posts, the two outer
stern posts a; a; may descend as low as the central one 6, but I prefer to have
the: outer stern posts of somewhat less depth than the central one at 6. When
the vessel has three stern posts, and is to be used in comparatively deep water
as compared with her draft, a single rudder may be hung on the central stern
post. Figure 10 shews a view of the stern of another vessel having three
stern posts, the centre one 6 descending below the two outer ones a, a, but the
outer ones may, if desired; be as deep as the centre one; Figure 11 shews a
longitudinal section of the vessel shewn at Figure 10; and Figure 12 is a
Diagram of the lines of the bottom of the hinder part of this ship or vessel.
b
ill
In witness" whereof, I, the said William' Macnab, have hereunto set
my hand and seal, this First day of May; in the year of our Lord
One thousand eight hundred and fifty-eight."
Witness,
JNO. ALCOCK.
W MACNAB. (L.S.)
'