Deck or IMPROVED COL.- STRUCTION, TO FACILITATE THE REPAIRING. BUILDING, OR RETAINING OF SHIPS AND OTHER FLOATING BODIES
Year: 1833

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
MITCHELL, of Brickfield, in the Parish of Ballymacarrett, County of Down, in-
the Kingdom of Ireland, Civil Engineer, send greeting.
WHEREAS I did, by Petition, represent unto His most Excellent Majesty
King William the Fourth that I had invented "A Deck or IMPROVED COL.-
STRUCTION, TO FACILITATE THE REPAIRING. BUILDING, OR RETAINING OF SHIPS AND
OTHER FLOATING BODIES," and that certain parts employed in the construction of
the said dock of my Invention were also applicable to other purposes; and
His said Majesty, being willing to encourage all useful inventions, did issue
His Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Fourth day of July, in the fourth year of His reign, whereby
His said Majesty did, for Himself, His heirs and successors, give and grant
unto me, the said Alexander Mitchell, His especial licence that 1, the said
Alexander Mitchell, my executors, administrators, and assigns or such others
as I, the said Alexander Mitchell, my executors, administrators, and assigns,
should at any time agree with, and no others, from time to time and at all
times during the term of years therein expressed, should and lawfully might
make, use, exercise, and vend, within England and Wales and the Town of
Berwick-upon-Tweed, my said Invention; in which said Letters Patent there
is contained a proviso obliging me, the said Alexander Mitchell, by an instru-
ment in writing under my hand and seal, particularly to describe and ascertain
[Price 8d.]

page_text: the nature of my said Invention, and in what manner the same is to be per-
formed, and cause the same to be enrolled in His Majesty's High Court of
Chancery within six calendar months next and immediately after the date of
the said Letters Patent, as in and by the same, reference being thereunto had,
will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Alexander Mitchell, do hereby declare that the nature of my said Invention,
and the manner in which the same is to be performed, are described and
ascertained in manner following:-
My Invention of a Dock of Improved Construction, to facilitate the
Repairing, Building, or Retaining of Ships and other Floating Bodies, consists
in the application of several close water-tight boxes or cases, or rafts of timber,
combined in such a way as to form a flooring, for the support or carrying or
bearing upwards of the vessel or other body to be repaired, by the buoyancy
or power of floatation of the said boxes or rafts in water. And in my mode of
applying such boxes to the specified purpose. I propose to employ commonly
for retaining the pontoons in their proper places. piles, posts, or beams, or
mooring chains attached to metal pins, furnished at their lower ends with
a spiral flange or worm of metal, for the purposes of facilitating their introduc-
tion into or extraction from the ground, and of giving them a firmer hold
therein; which piles or mooring chains, with their pins so armed, are also appli-
cable to other purposes; for which other uses I claim them as parts of my
present Invention under these Letters Patent. I employ these close boxes,
commonly known by the names of pontoons or caissons, or the rafts of timber,
in some cases, of such magnitude and in such number as shall be adequate to
support out of the water, by their combined buoyancy, the largest vessel of the
class the dock is designed to take in; and 1 so affix the pontoons to each
other, and station them in a tidewater not exposed to swell or strong current,
that they may rise and fall together with the ebb and flux of the tide, or that
they may be retained at pleasure at their low-water lever whilst the water of
the flowing tide rises above them.
admeasurement below or not much exceeding sixty-four feet keel and eighteen
feet beam, I propose to employ three caissons, of the dimensions of about forty
feet in length, fourteen and half feet in width, and three feet in depth,
outside measure. These caissons must be sufficiently strongly framed and
timbered to bear the strains and pressure to which they will have to be
exposed, and seamed so securely as to prevent, as much as possible, leakage
under the great pressure of their load. For caissons, of the dimensions above
stated, I recommend that the floor timbers should be a keelson of at least
For a floating dock to hold vessels in

page_text: twelve inches square, with two other long joists or timbers about eight inches
square, lying longitudinally midway betwixt the keelson and side picces,
and that the side and end pieces of the floor frame should be about fourteen
inches wide by eleven inches deep. These floor timbers should be natched
together, and laid flush on their lower sides. The corner pieces may be
short pieces of fourteen inches square, natched into the angles of the
floor frame, and set upright, and the side and end timbers about eight
inches square, natched and set upright in like manner upon the exterior
timbers of the flooring. These may be set at about eighteen inches space and
timber. On the inner faces of the upright timbers, cleats, running the length
of the sides and ends, should be aflixed, to take the ends of the deck beams
and of the deck planks; the upper surface of the side cleats being below the
top of the timber about four inches, that of the end cleats on the level of the
top of the beams. The deck beams should be about eight inches square, and
distant from each other three feet, beam and space; they should be dovetail
natched at the ends into the cleats. The cleats may be at first spiked to the
side timbers, but when the side planks are put on the same trenails which hold
the planks may pass through the cleats and hold them too. The cleats may
be about eighteen inches deep, six inches on the upper face and three inches
on the lower. The floor planks run transversely about twelve inches broad
by three inches thick, and are trenailed to the flooring timbers. The side
and end planks should be to have as few seams as possible; eighteen inches
broad, five inches thick, and trenailed to the upright timbers. The deck
planks run lengthways of the vessel, about six inches broad by two and
a half inches thick, and nailed to the beams. In laying the side and end
planks, it should be observed that the outer ends of the upper side planks
should come flush with the ends of the caisson, and the outer ends of the
lower end planks flush with the sides of the caisson, that the downward
pressure may not tend to open the seams. To give greater stiffness to
the vessel, to resist pressure from without, braces may be set in the way
of principals, from notches near the ends of the keelson up to the middle
beam, through which a king bolt may be passed, to be screwed down by
a nut to a stirrup iron bolted across the middle of the keelson. Shores
or props may also be fixed betwixt the beams and the flooring timbers
in their lines of intersection. To make a platform of the caissons or
floor of the floating dock, they must be placed in the water parallel to each
other, about five or six feet apart, and connected by strong beams laid
across their decks, and running the whole length of the proposed flooring.
Two of these beams, about sixty feet in length, or rather more, and fourteen

page_text: inches square, are to be laid across the caissons at equal distance from the
middle transverse line, and about eight feet asunder. These we will call the side
strokes, and across them transoms are to be laid, on which the keel of the ship
or vessel is to rest. Two other beams of similar scantling are to be slit, and
the flitches, blocked apart to the distance of thirteen or fourteen inches, are to
be bolted together in pairs anrl placed parallel to the side strokes, the openings
betwixt the flitches being vertical, within about eight feet of each end of the
caissons. These double or slit timbers we may distinguish by the name of
holding beams. All the long beams lying across the decks of the caissons
must be made fast to cach caisson in some suitable way, so as to lock together
the whole floating platform. The mode exhibited in the Drawings, by straps,
staples, and pins, is efficient and convenient, as allowing the caissons to be
shifted farther from or nearer to each other at pleasure. The spaces betwixt
the flitches of the holding beams are to admit the passage of the piles which
retain the dock in its situation in the water, and must be sufficiently wide to
allow of the easy rise and fall of the dock with the tide by their guidance.
To retain the dock in its situation, but to allow it when necessary to rise and
fall with the tide, I commonly employ piles set upright in such a way as to
prevent the current from displacing the floating flooring, and at the same time
to serve as guides to it in its motions of ascent and descent with the variable
level of the water. The mode of arranging 'the piles, as shewn in the Drawing
Fig. 1, where they pass through the spaces betwixt the flitches of the holding
beams, is generally perhaps the more convenient for the business of a repairing
dock, but circumstances may occur under which this mode of placing them
may be departed from with advantage. The piles, so to be employed for
retaining the floating dock in its situation in the tide water, may be of the
ordinary kind, namely, beams or sticks of timber pointed or cut wedge-shaped
at their lower extremities, and shod so as to admit of their being driven firmly
into the ground by the ram in the ordinary way; and I should consider my
floating dock fitted with such piles to be completely effected for all its designed
purposes, but in the place of such ordinary piles I prefer to use, in the con-
struction of my aforesaid dock, piles otherwise fashioned, and fitted with an
apparatus by means of which they can be inserted into the ground without the
aid of a ram or pile driver, can be easily removed therefrom at pleasure. and
by means of the same, when in the ground, they have greater power of resisting
upward or downward pressure. The apparatus which I so employ to give the
piles these properties is a broad and short worm or screw of cast iron fitted on
the lower extremity of the stick. This worm is a broad flange coiling helically
about one and a half turns round a hollow socket, and cast together of .one

page_text: piece, the worm plate thinning off gradually from where it springs from the
socket to its outer margin. The circumferential line of the worm describes
a double volute in reference to the axis of the socket, curving spirally inwards
towards the centre at both its terminations. Such a form facilitates its
cutting through the ground, and with the same view the edge is made more
acute on those portions of the curve which run in towards the socket. The
socket is a short tube, either cylindrical, conical, or prismatic, which receives
the lower end of the pile, shouldered down and shaped to enter and fill its
cavity, and having its extremity passing a little through the socket shod with
a conical iron ferule to enable the instrument more readily to penetrate the
ground. Two or more thorough pins driven through the timber and holes in
the socket, and rivetted at the ends, secure the worm to the pile. The piles
so armed can be readily inserted into penetrable ground by setting them verti-
cally in their assigned places, their points downwards, and turning them round
by means of cross levers. In the same way, by a reverse rotation, they can be
readily withdrawn when occasion requires. In some cases, where it may be
thought expedient for merely temporary purposes to dispense with the insertion
of piles to retain the dock, or where the force of the current may make it
advisable to use means to lessen the lateral stress upon the piles when used.
I employ the same kind of worm as above described fitted with a central pin
of iron and a shackle on a loose collar, to obtain through a strong chain a
secure and convenient mooring. The central iron pin for this form of the
apparatus is pointed below, and fits into the tapering cavity of the socket, the
pointed end passing through and above the upper margin of the socket; it
stands up so far as to admit on the upper part of the shaft of the pin, which
is cylindrical, a strong collar of iron, which turns easily upon it, betwixt the
margin of the socket and projecting shoulder on the pin. The central pin
and the socket are fixed to each other by strong thorough pins. The head of
the central pin above the shoulder is made pyramidal or prismatic to
receive the key, which is used to turn it into or out of the ground. The
loose collar has two projecting journals forged on it to receive the eyes of a
shackle, by which a mooring chain is connected with it. This loose collar
allowing the pin to turn within it whilst the worm is being screwed into or out
of the ground by means of the key, prevents any impediment to the operation
from the chain. The key for acting on this screw mooring is a socket of
iron, fitting upon the head of the central pin. and having a shaft of
suitable length for the proposed depth of water, and of insertion into
the ground. I find it convenient to make the shaft for the key of wrought
iron tube in about ten feet lengths, four to six inches diameter, and one

page_text: On
quarter or three eighths thick. These tubes, filled with wood inserted wedgewise,
are solid and light, and resist torsion with sufficient power. The lengths, of
shafting may be conveniently jointed together by a short pin or piece of smaller
tube fitting within the outer tube at one end, and projecting eight or ten inches out
of it, so as to receive upon it the end of the next piece of shafting; fixed and move-
able steel pins passed through the outer and inner tubes will hold them together;
but to connect the lengths more securely to resist torsion, it will be advisable to
scarf or notch the ends of the outer tube so as to fit like teeth into each other.
To obtain a hold of the shaft for the purpose of turning in or out the mooring
screw, it may be necessary to weld or pin upon the shaft, at convenient distances
for allowing the cross levers to be worked, angular bosses, on which a plate
key will fit, and can be passed over from one to another. The piles for a
floating dock should be sticks of timber of twelve or fourteen inches square,
and of sufficient length to stand five or six feet above high-water mark at
spring tides when inserted from twelve to twenty feet into the ground. All the
tide range of the pile should be left square; the lower part may have the
angles dressed off and be gradually rounded as far as it is to enter the ground,
and tapered and shouldered to fit into the socket of the worm. To stiffen this
portion of the pile against twisting, strong hoop iron may be coiled and nailed
upon it spirally in a direction contrary to that of the thread of the worm.
the two opposite flat faces of the piles which are to stand parallel with the
long timbers of the dock, plates of iron, of from four to five feet in length
about six inches broad and three quarters of an inch thick, are laid in flush
and screwed or bolted on, the lower ends of the plates being about low-water
mark. These plates are perforated correspondingly with holes of from two
and a half inches to three inches diameter and about three inches apart, and the
timber is to be bored coincidently with the plate holes to allow a wrought iron
pin filling the bore to pass through. As the dock rises and falls with the tide
the flitches of the holding beams will move along the faces of the perforated
plates; but when it is necessary to hold down the flooring of the dock, to
prepare it to receive a vessel, the iron pins stretching across the flitches of the
holding beams must be introduced into the proper holes at low water, and
the tide will then flow over the caissons and flooring timbers. To stiffen the
piles as they stand in their places, by tying then one to another, and at the
same time to obtain a convenient gangway, a platform of planks is fixed on.
the heads of the piles running the whole length of the dock on each side. To
keep the vessel in its upright position until the water leaves the floor of the
dock, there must be bearing bars which can be brought up and held securely
against the vessel's sides by shores. These may be efficiently arranged in the

page_text: following way-On the sides of the caissons there must be bolted or screwed
strong perforated iron plates corresponding in length and situation with the
spaces betwixt the side strokes and the holding beams. The plates may be
about seven feet long, five inches broad, and half inch thick, and perforated
with a row of holes of one and a quarter inch diameter and one foot apart.
The plates must be so set that the holes come opposite to near the lower
edge of the cleats on the side timbers, in order that the pins which are to pass
into the plate holes may go through the planks and cleats to get a stiffer hold,
and being drawn inwards by nuts on the tails of the pins, give some additional
strength to the sides. The pins should have conical shoulders to drop into
counter-sunk holes in the plates, and the tails may taper inwards where they
pass through the planks and cleats. that as they are drawn up by the nuts they
may be made to fill completely the holes in the timber projecting outwards
beyond the plate; the pins should be cylindrical, and have six or seven inches
of length. Pieces of oak scantling, about twenty feet long, nine inches broad,
and five inches thick, having an iron hoop near their lower ends drilled to
admit the projecting pins, are set on the pins, one for each side of the vessel,
on both sides of each caisson, so that they are carried on the pins and can turn
upon them as centres through a certain range. They may be secured on the
pins by cotters and washers, and readily shifted from one pin to another,
according to the different breadths of vessels to be supported.
The upper ends
of these supporting pieces or bearing bars, when thrown back preparatory to
the admission of the vessel into the dock, rest against the edge of the gang-
way on the pile heads. To bring the supporting pieces up against the sides of
the vessel, and hold them there. shores are placed behind them having their
abutments in cast iron shoes bolted upon the decks of the caissons, their upper
ends pressing against the back edges of the supporting pieces, and being pre-
vented from slipping sideways by a clip of iron on each side; these shores may
be brought forward and made to press the supporting pieces up against the
ship's sides, and to hold them there by a tackle strained betwixt the upper end
of the shore and a ring bolted into the deck of the caisson, as shewn in the.
Drawing. To prepare the dock for receiving a vessel, it will be necessary at
low water to pin down the flooring by passing the strong pins through the
holes in the piles nearest above the upper surface of the holding beams.
The supporting bars are to be thrown back to rest against the gangway. The
transoms lying across the side strokes, at about six feet apart and blocked
under their middle, are to be secured in their places by dogs. The rising tide
will then flow over the flooring of the dock. At high water the vessel to be
docked must be brought into such a situation that its keel, as the vessel drops

page_text: with the ebbing tide, will take the middle of the transoms. This may be
readily accomplished by making the bearing bars to press against her sides by
pulling at the tackle falls from the gangway. When she has settled down into
her place and rests upon the transoms, the decks being left by the water, the
vessel must be made safe in her upright position by shoring from the decks of
the caissons to her sides. At low water the pins may be struck out of the piles,
and with the returning tide the vessel will be borne up by the buoyant flooring.
When the vessel is to be removed from the dock the flooring must be again
pinned down at its low-water level, and the rising tide will then float off
the ship.
In the Drawings which accompany this description, and form part of my
Specification, the same parts are in the several Figures distinguished and referred
to by the same letters or marks, and the parts, connected in construction are
drawn to scales marked on the Sheets. In the actual structure of such docks
the dimensions and proportions of the whole, or of parts, may be varied
according to circumstances.
Figure I., horizontal view of the dock. Figure II., transverse view.
Figure III., transverse section of a caisson. Figure IV., outside face of a pile in
connection with a holding beam and caisson. Figure V., a mooring worm or
screw, and its several parts. A, caisson. B, long beam named a side stroke.
C, long beam slit and blocked out, named a holding beam. D, transom. E,
pile. F, block. G, supporting piece or bearing bar. H, shore. I, gang-
way. K, worm. L, tackle. M, ship. N, cross levers to turn the piles.
a, pins and plates on sides of caissons. b. shoring shoe bolted on the deck.
c, holding straps or stirrups. d, cross pins to hold down the floor of the
dock when required. d. keelsom. e, floor timber. f, side flooring timber.
g, deck beam. h, side timber. i, cleat. 1, perforated plates on the faces of
piles. m, shoe or ferule of the pile. n, pin or shaft of the mooring screw.
o, loose collar. p, shackle. q, key for mooring pin. 7, section of key shaft. 8,
exterior of key shaft. t, angular boss for key pinned or welded on key shaft
at convenient distances for working the cross levers. The worm for the piles,
or for the mooring screws, may of course be varied in dimensions, say from
two to five feet, or more or less, according to the nature of the ground or the
degree of resistance called for by the work in which they are employed.
Now I declare my Invention to consist, in the first place, in the formation
of a graving dock with a buoyant floating, which being held down by any.
suitable contrivance at its level of low water in a tideway, when desired can be
subsequently liberated so as to rise and fall with the tide, and to carry upon it
the ship or vessel to be repaired or built; and I claim such a dock with a

page_text: floating floor to be of my Invention under the privileges of the before-recited
Letters Patent, whether the buoyancy of the floor be obtained by the means
of the hollow air-tight vessels. such as the caissons herein described, or by the
means of any other form of hollow air-tight vessel suitable for the purpose, or
whether the buoyancy of the floor may be derived simply from the specific
gravity of the materials employed in its construction being less than that of
the supporting medium.
And I claim as of my present Invention such a dock with a buoyant flooring,
whether the flooring be retained in its situation and guided in its rise and fall
by piles, as therein shewn, or otherwise arranged, or whether the movements
and position of such flooring be controlled and regulated by the means of
mooring chains or cordage, however arranged and made fast.
And I declare my Invention under the present Letters Patent further to
consist in the application to the lower end of a wooden pile, or to a metal pin
or shaft, of a broad metal screw or worm, for the purpose of enabling such a
pile or pin to be inserted or extracted from the ground, by causing it to turn
upon its axis by means of cross levers when it is placed with its point directed
upon penetrable ground.
And I claim, under the privileges of the before-mentioned Letters Patent,
piles, pins, or shafts, so armed with broad metal worms or screws, whether
the same be employed in the construction of a dock as herein described, or
for piling ground for the support of buildings or embankments, or to obtain a
secure hold of the ground for the purposes of mooring or holding fast ships and
other floating or stationary bodies.
And I further declare that I do not claim any exclusive right to the use
of such other things mentioned or described in this Specification which are
well known and of common use, except in so far as they may be applied to
the especial purposes of my Invention now specifier.
In witness whereof, I, the said Alexander Mitchell, have hereunto set
my hand and seal, the Fourth day of January, in the year of our
Lord One thousand eight hundred and thirty-four.

page_text: AND BE IT REMEMBERED, that on the same Fourth day of January,
in the year above mentioned, the aforesaid Alexander Mitchell came before
our Lord the King in His Chancery, and acknowledged the Specification
aforesaid, and all and every thing therein contained, in form above written.
And also the Specification aforesaid was stamped according to the tenor of
the Statute in that case made and provided.
Inrolled the Fourth day of January, in the year above written.