IMPROVEMENTS IN BREAKWATERS
Year: 1854

page_text: LETTERS PATENT to Jonathan Davidson, of Edinburgh, in the County
of Midlothian, North Britain, Machine Maker, for the Invention of
IMPROVEMENTS IN BREAKWATERS
"
Sealed the 20th June 1854, and dated the 24th April 1854.
PROVISIONAL SPECIFICATION left by the said Jonathan Davidson at the
Office of the Commissioners of Patents, with his Petition, on the 24th
April 1854.
I, JONATHAN DAVIDSON, of Edinburgh, in the County of Midlothian, North
Britain, Machine Maker, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN BREAKWATERS" to be as follows:-
This Invention relates to a system of protecting coasts, harbours, and other
exposed shores from the action of waves. When a sea or river is agitated,
there is always just as much water above the natural calm level as there is of
air below that level; hence the surface line during a storm is occupied in half
its space with water and the other half with air. To still the wave action, a
raft or platform of a specific gravity equal to half that of water is used. Such a
raft, by its portion immersed in water, will hold its other half suspended in air,
and it will always remain at the surface line of the water. The raft is to be
moored along the edge of the shore in a horizontal position, the mooring con-
nections being of course long enough to admit of the full rise of the tide; then.
as the wave is driven against the edge of the raft, the elevated water is above
the level of the raft, and in falling down upon the raft surface it passes through.
openings in the raft; the water thus arrives at its line of rest, and produces
stillness on the other side. Such a system of breakwater may be applied in
any situations where it is possible to moor the raft. For instance, a series of

page_text: such rafts may be arranged to encircle or close in a large area of water on an
exposed coast, or even in the open sea, so as to form a harbour of refuge. The
rafts may also be placed round lighthouses, so as to protect the erections from
all wave action.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Jonathan Davidson in the Great Seal Patent Office on the
23rd October 1854.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JONATHAN
DAVIDSON, of Edinburgh, in the County of Midlothian, North Britain, Machine
Maker, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-fourth day of April, in the year of our Lord
One thousand eight hundred and fifty-four, in the seventeenth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Jonathan Davidson, Her special license that I, the said Jonathan Davidson, my
executors, administrators, and assigns, or such others as I, the said Jonathan
Davidson, my executors, administrators, or 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 BREAKWATERS,”
upon the condition (amongst others) that I, the said Jonathan Davidson,
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 Jonathan Davidson, 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 statement,
reference being had to the accompanying Drawings, and to the letters and
figures marked thereon, that is to say :-
My said Invention relates to a system of protecting coasts, harbours, and
other exposed situations from the action of waves by means of a buoyant raft
or rafts constructed in a peculiar manner. This raft consists of a framework
of timber or other suitable material or materials, and to be made of a specific
gravity equal to half that of the water upon which it is to float, or the raft may

page_text: be of any specific gravity less than that of water, it being preferred,. however,
to have it, of half the specific gravity of water. The requisite buoyancy is to
be obtained, either by the empoyment of suitable materials, or by fitting hollow
air-tight boxes or vessels to the raft, in such a manner as to cause it to float
half in and half out of the water. This degree of buoyancy is given to the
raft in order that it may always float at or near what would be the level of the
water when calm, notwithstanding that the water may be violently disturbed;
for when water is by any cause thrown into the wave state, there is always an
equal or nearly equal bulk of water and air respectively above and below the
normal level or the level of the water when at rest; and as the raft will be
sufficiently supported by the water which happens to be at the normal level,
although this water will in the aggregate extend over only half the area of
the raft, it will remain at the normal level. In this position, the raft will sus-
tain or receive the perpindicular impact of the waves, and will communicate it
equally over the entire area of water covered by it, thus dissipating its intensity
and preventing its unequal and intermittent action, which would otherwise
propagate the undulation indefinitely. As the dimensions and minor details of
construction of my improved breakwater raft will vary considerably with the
locality which is to be protected by it, I can here merely describe the general
principles by which the practical engineer must be guided in carrying out my
plans. The raft must be of sufficient size as at least to cover three waves of
the largest size to which the locality may be exposed in severe weather, in
order that it may not undulate with the waves, and so prove wholly inoperative.
It must also be stiff and rigid, so as not to yield or bend to the shape of the
waves, and it must be moored so as to rise and fall freely with the tide. The
horizontal surface of the raft may either be entirely covered or closed, so that
the water cannot pass through it vertically; or it may be formed with openings,
being constructed, for example, of crossed planks of timber, set at greater
or less distances apart. In some cases also the openings may be variously
arranged, or they may be of various dimentions at diffirent parts of the same
raft or series of rafts; thus, for example, if the raft is constructed more
particularly with a view to the counteraction of a ground swell, it may be
made closed on the shore side, and with openings on the side towards the sea.
In some cases, also, as for a ground swell, for example, it will be advisable to
employ a valvular arrangement, which will allow the water to rise freely through
thic raft from below, but will prevent its direct return. This modification of
my breakwater raft will be more easily comprehended on reference to the
explanatory Figures on the Sheet of Drawings hereunto attached, and which
I shall now proceed to describe.

page_text: Figure 1 on the Sheet of Drawings is a side elevation of one modification
of niy improved breakwater raft; Figure 2 is a plan, corresponding; and
Figure 3 is a front elevation. Figures 4 to 10 represent certain details apper-
taining to the valvular arrangement, and these will be herein-after more
particularly referred to; they are drawn to a larger scale than that of Figures
1, 2, and 3. The raft is in this instance represented as composed of parallel
planks A of timber, crossed by similar planks B, and bolted together, to form a
stiff rectangular frame, which is moored by means of the chains C. Between
the upper planks B, and parallel to them, are placed a series of moveable
planks D, which are not bolted to the lower cross planks A, but aro confined
by strong iron staples E, in such a manner as to be able to turn on edge.
The staple E is represented in side elevation in Figure 4, the moveable plank
D being in 'transverse. vertical section. In Figure 5 the staple is shewn in
edge view, the lower cross plank A being in transverse vertical section; and in
Figure 6 the staple is shewn in plan, and as detached. This staple is bolted
by its flattened ends F to the plank A, and it passes up on each side of the
moveable plank D, and forms a quadrant-shaped space, within which the plank
D is free to turn on one edge, this edge being rounded for the purpose. The
planks D are prevented from moving longitudinally through the staples E by
means of snug pieces G, one of which is represented in elevation in Figure 7,
and in plan in Figure 8. The points H of these pieces extend past the staples
E, and the body portions G, by means of which they are fixed upon the plank,
defend the edge of the latter where it rubs against the staple in turning.
Figure 9 is an elevation, and Figure 10 is a plan, of a modification of staple of
increased length. It consists, in fact, of two staples, such as those already
herein-before described, joined together, as it were, and additionally strengthened
by a tie piece I at the top; or the planks D may be connected or hinged in
any other convenient manner, either to the lower planks A, or to the upper
fixed planks B. With these arrangements the planks D will turn on edge, so
as to allow the water to pass through freely from below, whilst on the water
descending-they will close and check its action. In the modification repre-
sented in the Drawings, interstices are left between the planks B and D, and
the interstices are of about the same width as the planks themselves. These
interstices, however, may be enlarged or reduced in size, or they may be
altogether dispensed with, the entire surface of the raft being filled up when
the moveable or valvular planks D are closed; or again, the interstices may be
varied in size at different parts of the raft or rafts, whilst the valvular arrange-
ment may be confined to portions of the raft or rafts; or it may be extended
over the entire breakwater. In Figures 1 and 2 on the Sheet of Drawings

page_text: is represented a means which may be employed to render the raft sufficiently
buoyant when the materials of which it is composed are not of themselves
light enough for this purpose, this consisting of a series of air boxes K, which
are fitted to the under side of the planks A. These boxes are represented as
made of wood, but metal or any other suitable material may be employed for
the same purpose. In some cases it will be adviseable to employ two break-
water rafts or lines of raft, one being moored near the shore and one further
out to seaward, the quiet water being between the two. This arrangement
will be desirable, for example, where there is a ground swell, accompanied by
surface waves caused by a strong breeze.
Having now described and particularly ascertained the nature of my said
Invention, and the manner in which the same is or may be used or carried
into effect, I may observe, in conclusion, that I do not confine or restrict
myself to the precise details or arrangements which I have had occasion to
describe or refer to, as many variations may be made therefrom without
deviating from the principles or main features of my Invention; but what
I consider to be novel and original, and therefore claim as the Invention
secured to me by the herein-before in part recited Letters Patent, is,
First, the general arrangement and construction of breakwater rafts, as
herein-before described..
Second, the application and use, for protecting coasts, harbours, and other
similar situations from the action of waves, of breakwaters, consisting of rafts
of a specific gravity less than that of water, and made of a size and rigidity
sufficient to prevent them from undulating or bending with the waves, as
herein-before described.
Third, the system or mode of constructing breakwater rafts with moveable
parts arranged to allow the water to pass freely through them in an upward
direction, but so as to check the descent of the water, as herein-before
described.
In witness whereof, I, the said Jonathan Davidson, have hereunto set my
hand and seal, this Nineteenth day of October, in the year of our Lord
One thousand eight hundred and fifty-four.
JAMES CRAIG, Witness.
ALEXANDER WESTWOOD, Witness.
JONN DAVIDSON. (L.S.)