IMPROVEMENTS IN APPARATUS TO BE USED IN LIEU OF A COFFERDAM FOR MAKING EXCAVATIONS UNDER
Year: 1873

page_text: LETTERS PATENT to John Napier, of 18, Finsbury Circus, in the
City of London, for the Invention of "IMPROVEMENTS IN APPARATUS
TO BE USED IN LIEU OF A COFFERDAM FOR MAKING EXCAVATIONS UNDER
••
Scaled the 11th March 1873, and dated the 21st January 1873.

page_text: sufficient buoyancy to the apparatus to enable it to be floated to the
place where it is to be used and to be removed after use. Around tho
bottom of the pontoon a keel like ridge is formed-which is sharp at its
lower edge. The pontoon having been floated in shallow water to the
place where it is required for use is allowed to settle down until it rests
on the bottom, and the sharp kecl then penetrates to a sufficient depth to
cut off all communication between the exterior water and the space
enclosed by the pontoon. In order to cause the keel to penetrate to a
sufficient depth the compartments around the central opening are filled
with water.
Pumps are provided to pump out the water from the space enclosed
by the pontoon and the same pumps may be employed, if necessary, for
filling and emptying the compartments of the pontoon. Where there
is a sufficient tide the water can be run out and will not require pumping.
In some cases I make the pontoon three sided, so that when a portion of
a wall has been built up within it, it may be floated off lengthways to a
sufficient distance to enable the work to be continued, whereas otherwise
the work must not be carried so high as to prevent the pontoon being
floated away over the top of the work.
The sides of the pontoon are firmly braced together by girders which if
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said John Napier in the Great Scal Patent Office
on the 21st July 1873.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
NAPIER, of 18, Finsbury Circus, in the City of London, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent bearing date the Twenty-fifth day of January, in the year of our
Lord One thousand cight hundred and seventy-three, in the thirty-sixth
year of Her reign, did, for Herself, Her heirs and successors, give and grant
unto me, the said John Napier, Her special license that I, the said
John Napier, my executors, administrators, and assigns, or such
others as I, the said John Napier, my executors, administrators, and
assigns, should at any time agree with, and no others,. from time to

page_text: time and at all times thereafter during the term thercin 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 APPARATUS TO BE USED IN LIEU
OF A COFFERDAM FOR MAKING EXCAVATIONS UNDER WATER, AND FOR EXCLUDING
WATER FOR OTHER PURPOSES," upon the condition (amongst others) that I,
the said John Napier, 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 tho date of the said Letters Patont.
NOW KNOW YE, that I, the said John Napier, 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 apparatus to bo
used in lieu of a cofferdam for making excavations under water, and for
excluding water for other purposes.
The apparatus consists of a pontoon with an opening in the centro
surrounded by water-tight compartments, which when empty give
sufficient buoyancy to the apparatus to enable it to be floated to the
place where it is to be used and to be removed after use. Around the
bottom of the pontoon a keel like ridge is formed which is sharp at its
lower edge. The pontoon having been floated to the place where it is
required for use is allowed to settle down until it rests on the bottom
and the sharp keel then penetrates to a sufficient depth to cut off all
communication between the exterior water and the space enclosed by the
pontoon. In order to cause the keel to penetrate to a sufficient depth
the compartments around the central opening are filled with water.
Pumps are provided to pump out the water from the space enclosed
by the pontoon, and the same pumps may be employed if necessary for
filling and emptying the compartments of the pontoon. Where there is
sufficient tide the water can be run out and will not require pumping.
In some cases I make the pontoon three sided, so that when a portion of
a wall has been built up within it, it may be floated off to sufficient

page_text: compartments a¹ of the dam are now emptied, and the water is excluded
from them whilst it is allowed to flow freely into the space a³. Thus
the structure is caused to float with the rising tide until it has risen over
the top of the wall, when it is hauled away and can at once be adjusted
to a new position to construct another length of the wall. a", a³, arc
movable beams connecting the two sides of the pontoon dam so as to
give it rigidity and stiffness. Tho cutting keel or ridge a³ is very
strongly framed, so that it may not be liable to be distorted by any
obstacles with which it may meet. The portions of wall thus constructed
may be connected without difficulty by piling the spaces between them
on either side, as is shown at b, so as to form a small dam within which
the masonry is laid. Usually a single tide will suffice to complete in
this manner the connection between two lengths of walls built by means
of the pontoon dam as already described.
The sectional form of the pontoon dam may be varied, thus sections G
and H are forms which are suitable where a wide excavation is required,
as in dredging operations. As represented in these Figures the cutting
keel is constructed of strong plates supported by angle picces at
intervals:
In some cases I form the pontoon dam with three sides only. Figure 4
is a plan illustrating this arrangement; Figure 5 is an elevation partly
in section, and Figure 6 is a section taken on the line c, d, in Figure 4.
In this case a tic beam a³ is used to connect and support the two free
extremities of the structure; this tic beam as well as the smaller ties a",
a', is placed at such a height as not to interfere with the work to be
carried on within the space a³. When using a pontoon dam of this con-
struction the wall can be carried up further than when the pontoon dam
is so constructed as completely to inclose the space a³.
When onc
section of the wall has been completed the three sided pontoon dam is
floated and adjusted to the end of the wall so as just to overlap it in the
manner shewn by the Drawings. The pontoon dam when so adjusted
is caused to settle down on to the bottom in the manner already
described, and piling (as shewn at c, c,) is then driven between the wall
and the extremities of the pontoon dam so as to complete the enclosure
of the space a³.

page_text: arrangement will also admit of the use of the pontoons in the manner
illustrated by Figures 7 and 8 in examining the foundations of walls,
Figure 7 is a plan, and Figure 8 is a transverso section taken on the
line e, f, in Figure 7, piling is employed between the wall and the
pontoon dam as already described in respect to Figures 4, 5, and 6, and
in this manner the space a³ is enclosed at each end.
Having thus described the nature of my said Invention and tho
manner of performing the same, I would have it understood that I claim
the apparatus substantially as herein described, to be used in lieu of a
cofferdam for making excavations under water, and for excluding water
In witness whereof, I, the said John Napier, have hereunto set
my hand and scal, this Nineteenth day of July, in the year
of our Lord One thousand eight hundred and seventy-three.