_STEAM NAVIGATION--THE ‘GREAT EASTERN’ STEAM-SHIP. THE LAUNCH._
A.D. 1857--1858. ÆTATIS 52.
REASONS FOR DETERMINATION THAT THE SHIP SHOULD BE LAUNCHED
BROADSIDE TO THE RIVER--AND THAT THE LAUNCH SHOULD BE
SLOW--EXTRACTS FROM MR. BRUNEL’S REPORT OF FEBRUARY 1855--REASONS
FOR THE ADOPTION OF IRON SLIDING-SURFACES--DESCRIPTION OF THE WAYS
AND CRADLES--AND OF THE MOTIVE POWER PROVIDED FOR LAUNCHING THE
SHIP--MEMORANDUM ON PROPOSED ARRANGEMENTS FOR THE LAUNCH (SEPTEMBER
26, 1857)--LETTER TO CAPTAIN HARRISON ON RIVER TACKLE (SEPTEMBER
30, 1857)--LETTER ON THE NATURE OF THE OPERATIONS (OCTOBER 23,
1857)--MEMORANDUM ON GENERAL ARRANGEMENTS AND INTENDED MODE OF
PROCEEDING (OCTOBER 30, 1857)--HISTORY OF THE LAUNCH, NOVEMBER 3,
1857-JANUARY 31, 1858--LETTER TO THE DIRECTORS, NOVEMBER 26,
1857--REPORT AND MEMORANDUM ON THE LAUNCHING OPERATIONS (DECEMBER
17, 1857)--FLOATING THE SHIP--_NOTE A_: EXPERIMENTS AND
OBSERVATIONS ON FRICTION.--_NOTE B_: LETTER TO W. FROUDE, ESQ.
(FEBRUARY 2, 1858).
The mode in which, the great ship was to be launched had necessarily to
be determined before she was commenced. In May 1858, when the contract
for her construction was entered into, the question was left open, and
the contractor was either to launch her, or to build her in a dock ‘if
it be found preferable.’ With Mr. Brunel’s full concurrence, Mr. Russell
determined to build the ship on the river-bank, broadside to the river.
The reasons which led to this determination were fully described by Mr.
Brunel in his report of February 5, 1855. This report has, with the
exception of the parts relating to the launching operations, been
printed above, p. 315. The passages there omitted are as follows:--
One of the first points to be decided was the mode of launching the
vessel, which of course would determine the position in which it
was to be built; and I wish to take this opportunity of explaining
my reason for adopting the plan I have decided upon, which, being
unusual, might be supposed to be unnecessary.
Vessels are generally built above the level of high water, and then
allowed to slide down an inclined plane into the water;
occasionally, as in the case of the ‘Great Britain,’ they are built
in a dry dock, into which the water is afterwards admitted, and
they are floated out.
Both plans were well considered in the present case; but the size
of the dock required, the difficulty of finding a proper site for
such a dock, the depth required for floating a ship with her
engines and boilers, which it was most desirable to introduce while
building the hull, and the depth of channel required to communicate
between such a dock and the deep water of the river, all combined
to render the dock plan a very expensive, and, considering the
nature of the soil in which it would have to be formed, a somewhat
hazardous proceeding. Launching seems to offer the fewest
difficulties and the greatest certainty; but the dimensions of the
vessel required some modifications of the usual modes of
proceeding.
Launching is generally effected by building the ship on an inclined
plane, which experience has determined should be at an inclination
of about 1 in 12, to 1 in 15, the keel of the ship being laid at
that angle, and the head consequently raised above the stern, say
one fifteenth of the whole length of the ship. In the present case
this would have involved raising the fore part of the keel, or the
fore-foot, about 40 feet in the air, and the forecastle would have
been nearly 100 feet from the ground; the whole vessel would have
been on an average 22 feet higher than if built on an even keel.
The inconvenience and cost of building at such a great height above
ground may be easily imagined; but another difficulty presented
itself which almost amounted to an impossibility, and which has
been sensibly felt with the larger vessels hitherto launched, and
will probably, ere long, prevent launching longitudinally vessels
of great length. The angle required for the inclined plane to
ensure the vessel moving by gravity being, say 1 in 14, or even if
diminished by improved construction in ways to 1 in 25, is such
that the end first immersed would become water-borne, or would
require a very great depth of water before the forepart of the ship
would even reach the water’s edge. Vessels of 450 or 500 feet in
length would be difficult to launch in the Thames unless kept as
light as possible; but our ship could not be so launched, the heel
of the sternpost being required to be, as I before said, about 40
feet below the level of the fore-foot. Some mitigation of the
difficulty might be obtained by an improved construction of the
ways; but the great length of ways to be carried out into the river
would, under any circumstances, be a serious difficulty.
These considerations led me to examine into the practicability of
launching or lowering the vessel sideways; and I found that such a
mode would be attended with every advantage, and, so far as I can
see, it involves no countervailing disadvantages. This plan has
been accordingly determined upon, and the vessel is building
parallel to the river, and in such a position as to admit of the
easy construction of an inclined plane at the proper angle down to
low-water mark.
In constructing the foundation of the floor on which the ship is
being built, provision is made at two points to ensure sufficient
strength to bear the whole weight of the ship when completed. At
these two points, when the launching has to be effected, two
cradles will be introduced, and the whole will probably be lowered
down gradually to low-water mark; whence, on the ensuing tide, the
vessel will be floated off. The operation may thus be performed as
slowly as may be found convenient; or, if upon further
consideration more rapid launching should be thought preferable, it
may be adopted.
I have entered at some length into an explanation of all the
reasons which led to the adoption of this plan; as I am anxious
that they should be known, and particularly that it should be well
understood by the proprietors and those interested in our success,
that I am not adopting any novelties; unless, so far as those
modifications of the more usual practices which experience points
out as necessary to meet the peculiarities of a particular case may
be deemed such.
I should add that the necessity, arising from the same causes, of
launching transversely has been felt with long vessels of another
description, namely, pontoons, or floating piers; one of 300 feet
in length, which I have built at Plymouth, was so launched, and
previously to this, one of 400 feet in length by Mr. Fowler on the
Humber.[158]
I hope to be able to arrange that the machinery, which is to be
provided by the contractor, for lowering the vessel down the ways
will be also fitted to form a ‘patent slip’ arrangement for hauling
the ship up for repairs; so that, if it should be found desirable
to do so, such apparatus may be purchased for that purpose, and
fitted up at the port which the ship will frequent. With the view
of facilitating such an operation, or the grounding of the ship on
a gridiron for examination at low water, a sufficient extent of the
floor of the ship is formed perfectly flat, and is so strengthened
as to allow the ship when loaded to be grounded without being
unduly strained.
After it was determined that the ship should be built on the river-bank
instead of in a dock, and parallel to the river instead of at right
angles to it, the next point for consideration was, whether the ship
should be lowered gradually to low-water mark, or whether a free launch
should be attempted.
In a free launch the ship is allowed by the action of the force of
gravity to run down the ways at a considerable velocity. In the case of
the ‘Great Eastern’ there were insurmountable objections to this plan.
Some of them might have been overcome by mechanical appliances; but
these would have introduced complication and additional elements of
risk.
In accordance with the opinion which he had from the first entertained,
Mr. Brunel determined to move the ship slowly down the ways.
* * * * *
Subsequently to his determination to launch slowly, Mr. Brunel decided
to employ sliding-surfaces of iron instead of greased wood.
In ordinary launches the ways are thickly greased, so that there is
between the ways and the cradles a thick stratum of grease, which
renders the friction very small. The conditions, however, do not remain
the same throughout the passage of a ship down the ways; for, when she
has moved some distance, the cradle has been rubbing away and squeezing
out the grease; and therefore the part of the cradle which supports the
middle and bows of the ship meets with increasing resistance from
friction. Another and more serious cause of the destruction of the
lubrication arises from unevenness in the ways.
The result of the action of the friction between the wooden surfaces
after the destruction of the grease is sometimes so great that they
become mutually imbedded, the fibres of the wood being rolled up
together to such an extent that it has been found difficult afterwards
to separate the timbers. The increased friction due to the deterioration
of the sliding-surfaces of grease does not often produce failure in
ordinary ship launches, because the vessel, while still on the fresh
grease, acquires a momentum sufficient to carry it over the lower part
of the ways, notwithstanding the retardation resulting from increased
friction.
It was from a legitimate fear of the development of a retarding force
due to the destruction of the grease, that Mr. Brunel hesitated to
employ wooden sliding-surfaces. The ground was far from solid; and the
use of piles as a foundation for the ways would not have prevented the
possibility of excessive local pressure being brought on parts of the
surfaces. The heat produced by undue pressure at any point under the
great area covered by the cradles would tend to spread and aggravate the
evil; and, had any considerable portion of the sliding-surfaces become
wood-bound, the difficulty would have been far less remediable than in
the case of an ordinary launch, where the cradles and ways are
throughout accessible. But in the case of the ‘Great Eastern’ the space
between the ship and the ways, over a considerable portion of the area
covered by the cradles, was very confined, and it would have been a
most tedious, if not a hopeless, task to get at the injured part so as
to repair it properly.
At the end of the year 1856, when the construction of the ways had to be
commenced, Mr. Brunel acted upon his views as to the dangers attendant
on the use of wooden sliding-surfaces, and adopted iron. By this step,
although there might be some fresh difficulties to be encountered, the
disastrous consequences were avoided which might have followed from
employing wooden surfaces.
* * * * *
Under two places in the length of the ship the ground had been prepared
for the reception of the launching ways. These ways or inclined planes
were two in number, and reached to low-water mark. They were placed at
such positions as best to carry the weight of the ship without straining
her. The ways, as originally designed by Mr. Brunel, were each 80 feet
wide; but, with the desire of spreading the weight of the ship over a
still larger area, he decided to add 20 feet to each side of each way,
thus increasing their breadth to 120 feet. The ship’s head pointed down
the river; 180 feet of the bow projected beyond the forward way, 110
feet were unsupported between the two ways, and 150 feet of the stern
projected beyond the after way. The distance from the starboard side,
the side next to the river, down to low-water mark, was about 240 feet;
and the actual length of the ways, including the portion under the ship,
was about 330 feet.
At the same time that he decided to use iron as the sliding-surface, Mr.
Brunel adopted means for ensuring, as far as possible, the even
distribution of the weight upon the ways. With this object he did not
attempt to make them unyielding, but allowed them to yield slightly, so
that, like a cushion, they might adapt themselves to the under surface
of all parts of the cradles with a sufficient upward pressure. The ways
rested on the river-bank, and piles were used to prevent the earth under
the edges of the ways from swelling out at the sides, and yielding more
than the ground under the middle portion.
The ground having been prepared to the slope of 1 in 12, a layer of
concrete of about two feet in thickness was laid over the area of the
ways. On the concrete were placed timbers running at right angles to the
ship. These timbers, which were imbedded in the concrete, were 1 foot
square, with a space of 2 feet 6 inches between them. Across these
timbers, and parallel to the ship, were placed other timbers, with
intervals of 2 feet between them; and upon these again were laid rails
18 inches apart, parallel to the ways, and at right angles to the ship.
The rails were of the ordinary kind used on the Great Western Railway.
Thus the ways consisted of a network of timber resting on a thin bed of
concrete; and on the top of the timber network were placed the rails
which formed the actual sliding-surface.
* * * * *
The under side of the cradles consisted of iron bars, which were laid
parallel to the ship, and therefore across the rails of the ways. These
bars were each 1 inch thick and 7 inches broad, with an interval of 11
inches between the bars. Upon these bars was fixed 6 inches of hard wood
planking (see fig. 15, _a_), and on this again came the framing of the
cradles. Tapered timbers (_b_) were driven in, so as to fill up the
wedge-shaped space between the hard wood over the bars and the flat
bottom of the ship. On the side next the river, between these timbers
and the rounded part of the under side of the ship, were driven in
separate wedge-shaped pieces (_c_), which were secured to the timbers
below by long bolts, arranged so as to allow the removal of the
wedge-pieces when required. The means of unbolting the wedge-pieces was
an essential provision for floating off the ship, as they had to be
removed before she could move sideways off the cradles. Resting on the
lower timbers of the cradle were stout props (_d_), which pressed
against the ship’s side higher up than the wedge-pieces, and took part
of the weight, and spread it over the outer part of the cradle. There
were similar props (_e_) on the landward side of the cradles.
[Illustration: Fig. 15. Transverse Section of Ship, showing Ways and
Cradles.
_Scale of feet._]
There were 80 rails on each of the ways, and nearly 60 transverse bars
under each cradle; so that there were 9,000 intersections of the bars
and rails. As the ship and the cradles weighed 12,000 tons, each
intersection carried on the average a weight of 1⅓ tons.
* * * * *
After the construction of the ways was settled, the amount of power
required to move the ship down had to be determined.
The motive power was not simply the chains, tackle, presses, &c.; but
there was also the action of gravity. One motive power, then, was not
only available, but was inevitably present; and, as the ways were at an
inclination of 1 in 12, the motive power of gravity upon the weight of
12,000 tons was 1,000 tons. The question to be decided was, whether the
1,000 tons of motive force was sufficient to overcome the friction; and,
if not, then what additional force would be required to do so.
* * * * *
In January 1857, immediately upon the adoption of iron sliding-surfaces,
an experiment was arranged on a considerable scale, in order to form
some idea on this important point. Two rails were laid at an inclination
of 1 in 12, and upon them an experimental cradle was placed, weighing
some 8 tons, and representing a small portion of the actual cradle.
The effect of the friction of iron sliding-surfaces may be summed up
very simply. It appeared that the motive power need not, at most, be
more than would have been given by placing the ways at an inclination of
1 in 8, and that restraining power could not have been safely dispensed
with if the ways had been placed at a greater inclination than 1 in 16;
as it was observed that, contrary to received notions, the friction
became less as the velocity increased, and that, in case any
considerable velocity were attained, a great force would be required
merely to overcome the motive power of gravity down the incline,
independently of that required to destroy the velocity.[159]
The task of getting the ship from the place where she was built to her
moorings in the river divided itself naturally into two parts--the
moving of the ship down the ways, and the floating her from off her
cradles.
This subdivision of the whole undertaking of the launch into two almost
distinct operations is of great importance in considering the manner in
which Mr. Brunel conducted them; especially when it is borne in mind
that one, the moving down the ways, was capable of being, by careful
precautions, rendered almost safe; whereas the other, the floating the
ship off, was dependent on the successful issue of various minor
operations, in the management of which the fallible human element had a
greater share, and where small accidents, though, in their primary
effects, productive only of delay, might cause irretrievable disaster.
* * * * *
In the operation of lowering the ship, there had to be provided both
power to move her and power to check her motion. In floating, but one
force was necessary, namely, that required to pull the ship off if she
got jammed on the cradles.
* * * * *
With a desire to provide for the possibility of an extreme amount of
resistance on the ways, Mr. Brunel designed a complete hydraulic
apparatus, which would have been sufficiently powerful to move the ship
down without interruption or delay. It is much to be regretted that he
did not persist in carrying out his original intention.
In the operation of floating, chains and tackle were the best means of
supplying the tractive force that might be required; and Mr. Brunel
decided to have a very large amount of available power. If the weather
were fine, and the tide at its calculated height, if no part of the
cradles got disarranged, if the calculations as to the ship’s draught of
water were correct--if everything went right, there would be no
necessity for any great hauling power; a few tug-boats would suffice to
take the ship to her moorings. But Mr. Brunel determined that in this
critical operation of floating he would not trust to good fortune, when
the absence of it might produce grave injury. The power which he thought
it desirable to provide in chain purchases for the floating was very
considerable, being equal to a pull of 500 tons.
As it seemed probable that the ship would not require much force to move
her down the ways, it seemed also probable that the river tackle (as the
chains and appliances for hauling the ship off were called) would be
sufficient for both purposes. This being the case, it at the time
appeared right, in the embarrassed state of the Company’s finances, to
dispense with the more powerful and costly apparatus which Mr. Brunel
had proposed for moving the ship down; there being no fatal consequences
to be apprehended from a defect of power.
Influenced by these considerations, Mr. Brunel resolved to trust to the
river tackle alone.
He referred to this decision in a letter to the Secretary of the Company
written during the launch:--
November 26, 1857.
My original intention, the right one, was to fit up properly such
an hydraulic apparatus as should be fitted to move the ship the
whole length of the ways, and to depend upon the whole river tackle
only in the event of her moving very easily, and for getting her
off the ways at the end. From an unwise attempt to economise I
determined to dispense with the immediate costly apparatus for
pushing, and by sufficient power merely to move the ship at
starting or in the event of sticking,[160] and to depend upon the
same river tackle to keep her moving down the ways.
The experiments made with the trial cradle had shown the necessity of
providing a certain amount of restraining force. As will be seen in the
description of the launch, it was only used once, but it must not
therefore be supposed that there was no necessity for providing it.[161]
The arrangement of the checking gear was the same at each of the ways.
Attached to the land side of the cradle, by means of bolts, was a strong
iron framework which held two large horizontal wheels or sheaves. At the
upper end of the ways another sheave was fixed in a strong timber
framing; and opposite the middle of the upper end of the ways was placed
a large windlass or drum.
This drum was a cylinder, about 20 feet long and 6½ feet in diameter, of
solid timbers, strongly bolted together, and secured at each end in a
broad cast-iron disc, 12 feet in diameter.
To a point in the framing was attached one end of a 2⅝-inch chain
cable; this chain was passed round one of the sheaves attached to the
cradle, then round the sheave attached to the upper end of the ways,
then round the second sheave attached to the cradle; and its end was
coiled round the drum. Thus, as one end of the chain was secured, it was
necessary, before the ship could move down the ways, that the drum
should revolve, and slacken the end of the chain coiled round it.
Round the discs of the drum were wrought-iron straps; these, when
tightened by levers, formed brakes by which the revolution of the drum
could be retarded. Gearing was provided with a train of toothed wheels,
so that the drum could be turned round by handles, and the chain wound
on to it.
The following paragraph is from the commencement of a memorandum by Mr.
Brunel on the launching arrangements, written about five weeks before
the launch began:--
September 26, 1857.
It is expected that, with the present construction of the ways, the
friction and the tendency to descend by gravity will be about
balanced; so that when once in motion no very great amount of power
(at least, in proportion to the mass to be moved) will be required
to keep the vessel in motion, or to check it if disposed to move
too quick, or quicker at one end than at the other; still the
forces which may be required either to help it on or to check it,
though relatively small as compared with the mass to be operated
upon, will be very large as compared with forces usually obtained
by the ordinary means of rope or chain purchases, and at the first
start, or after any accidental or intentional stoppage, a still
larger power may be required.
The apparatus which Mr. Brunel prepared for performing the double duty
of moving the ship down the ways and hauling her off the cradles was as
follows:--At each end of the ship was a powerful chain tackle. One end
of a chain cable was secured to a mooring in the river, and it was
passed round a large sheave attached to the ship, then round a sheave
fixed on a barge about 300 feet from the ship, and the end brought on
shore, where it was hauled on by a chain tackle worked by a steam crab.
The sheave attached to the ship at the bow was slung by chains about 80
feet from the stem. The sheave at the stern was fixed on the end of the
screw shaft. These purchases were intended to be good for 80 and 100
tons respectively, and were to be able to follow up the ship quickly if
she moved.
In addition to these purchases, Mr. Brunel desired to have ‘the means of
bringing a considerable strain to bear in the event of the ship sticking
at starting, or at any subsequent time, and particularly at the last;’
and he considered that ‘nothing under 250 or 300 tons would be of any
use for the purpose.’ This power he desired to apply to the centre of
the ship between the two cradles by means of double crabs and treble
purchase blocks on four barges.
One of the double crabs was mounted on each of the four centre barges,
and was placed on a platform, elevated so that the blocks of the chain
tackle could pass underneath it. This tackle was made fast to a chain
attached to the ship; and the mooring chain extending across the river
was hauled on by the tackle.
Each of these four crabs and tackle was to be capable of working up to a
strain of 80 tons. The strain which Mr. Brunel intended to be able to
put on the ship by the river tackle, in the form of a good continuous
pull, was in all 500 tons.
Two hydraulic presses were also provided, one at each of the cradles, to
overcome adhesion in first moving the ship. Each of these presses should
have been able to exert a strain of 300 tons. Therefore, including the
force of gravitation, the power which Mr. Brunel hoped to have to start
the ship was 2,100 tons, or more than one-sixth of the weight to be
moved; and for a continuous steady pull to keep her moving, 1,500 tons,
or one-eighth of the weight.
* * * * *
It was at one time thought possible that the launch might be effected in
October. But it was found that it would be impossible to be ready before
the spring-tides at the beginning of November; and even then, when the
time came, there was considerable hurry, and important matters were, as
will be seen, insufficiently attended to.
The cradles were put together and wedged up under the ship, and every
effort was made at low water to extend the ways as far as possible; so
that, by moving her further down the slope, a greater margin might be
obtained, to allow for any falling off in the expected level of the
tide, or for any miscalculation in the ship’s draught.
In the memorandum already referred to on the launching arrangements Mr.
Brunel instructed Captain Harrison to superintend the moorings for the
river tackle, and to satisfy himself of their sufficiency. A few days
afterwards he wrote to Captain Harrison on the subject:--
September 30, 1857.
I fancy (I may be wrong) that you hardly estimate sufficiently
highly the forces that we may require to get the ship down if she
sticks at all, or to drag the cradle from under her, or to force
her off the cradle at the last. She _may_ move down pretty easily,
and the cradles _may_ possibly not stick; but if she does stick at
all, it is as likely to require a dead pull of 500 tons as not, and
we must not shut our eyes to the real exact amount of strain which
may and will come upon purchases and moorings, &c., if this force
is required and is exerted; but we must provide for it. The several
moorings must really be good for the 80 and 100 tons respectively
mentioned in the memorandum--and we must not rest satisfied with
the feeling that the moorings are stronger than any generally sold
or than common tackle will effect, but must apply purchases that
will produce the strain, and if necessary we must strain them to
it; and our moorings ought to be beyond a doubt.
We are going to move 11,000 tons, a far greater weight than ever
was moved before, and we must not hesitate at providing a clear
pull of 500 tons; but bear in mind that 500 tons clear pull is
something much beyond what one is accustomed to. The power usually
brought to bear with purchases, chain cables, &c., is never
measured, but is very small; and we must take care and not be
misled by comparison with them. 80 tons is a heavy pull, and
nothing under 2 or 2¼ chain will be safe....
These are great strains we have to deal with, but they must be had,
and therefore we must meet them boldly.
Frequent enquiries were now made relative to the time of launching; and
the number of applications which poured in for admission to the yard led
Mr. Brunel to write the following letter to the Directors of the
Company, and it was published by them in the newspapers. In it he not
only removed current misapprehensions as to the nature of the proposed
operations, but he also took the opportunity of pointing out that there
would be no risk to the ship in the mode of launching adopted, and that,
although it might at first be unsuccessful, further power could be
applied, and the ship safely launched.
October 23, 1857.
The difficulty of replying to the numerous enquiries made
respecting the period at which the ship will be launched seems to
render it desirable that some means should be taken of giving the
information generally, that it may be uncertain, up to the end of
next week, whether the ship will be launched on the 3rd proximo or
the 2nd of December, and also of correcting the erroneous
impressions which exist as to the nature of the operation, which
can only lead to the disappointment of those who are erroneously
anticipating a display, on an unusually large scale, of that which
is a beautiful spectacle with ships of ordinary dimensions.
As regards the period of the launch I have, for some time past,
calculated upon being ready by the first tides of next month, and
by the unwearied exertions of those on whose assistance I have
depended, with the advantage of unusually fine weather, the
principal works required are so far advanced that there seems every
prospect of success; but a change in the weather is threatening,
the time remaining is short, and comparatively small causes may
create such delay as to render it more prudent, if not unavoidable,
to postpone the operation until the following available tide,
namely, that of December 2. As no mere desire to launch on the day
supposed to have been fixed will induce me to hurry an operation of
such importance, or to omit the precaution of a careful and
deliberate examination of all the parts of the arrangements after
all the principal works of preparation shall have been completed,
should such postponement prove necessary or be adopted from
prudence, everything having been now prepared, the launch would be
on December 2.
As regards the nature of the operation, it has frequently been
stated, but it seems necessary to repeat it, that the ship will not
be ‘launched,’ in the ordinary sense of the term, but merely
lowered or drawn down to low-water mark, to be thence floated off
by a slow and laborious operation, requiring two and possibly three
tides, and very probably effected partly in the night, and at no
one time offering any particularly interesting spectacle, or even
the excitement of risk; as I am happy to feel that, even assuming
accidents to occur or miscalculations to have been made, rendering
the operation unsuccessful--the ship may stop halfway or not move
at all, more power or other remedies may have to be applied--but no
injury to the ship can result from any failure in the course of
proceeding in this mode of launching.
Throughout October an immense amount of work had to be done, and the
multiplicity of matters to be attended to pressed heavily on Mr. Brunel
and his assistants.
With the check tackle he had reason to be content. The chains, which
were the ship’s cables, had been very carefully made; and, in addition
to the usual tests, pieces had been taken at hazard, and were found to
bear a good breaking-strain.
The river tackle was not so satisfactory. In operations that have to be
conducted afloat unexpected delays arise, and all the work may be
suspended by bad weather, and it is moreover frequently dependent on
tides. In the present case the work to be done was not easy. Heavy chain
cables had to be laid out, and moorings picked up and connected to the
tackles; one work having often to wait for the completion of another.
Mr. Brunel had determined that each purchase should be tested by being
strained to the utmost stress for which it was intended; but, owing to
the delays which had occurred in preparing the river tackle, this was
not done.
* * * * *
A few days before the launch Mr. Brunel addressed the following
memorandum to all who were to take part in the operation:--
_General Arrangements and intended Mode of Proceeding._
October 30, 1857.
It is desirable that all engaged in directing any part of the work
should understand the general course of proceeding which it is
intended to pursue, so far as may be found practicable;
circumstances may modify these pre-arranged plans, and may compel a
total departure from them, but every endeavour will be made to
adhere to them.
GENERAL COURSE OF PROCEEDING.
[Sidenote: To start about noon of Tuesday.]
I propose to commence operations about two hours before high water,
or about noon, and to endeavour to get the ship down as quickly as
I can into the water, and down to within about 36 feet of the
bottom of the ways.
My object in starting at this particular time of tide would be to
get the ship into the water, and waterborne to some extent as soon
as I could.
[Sidenote: Stop short of end of ways.]
I propose to stop short of the end, in order to avoid the necessity
of having to knock away all the shores, and clear the cradle at the
evening tide, when it would be dark, and to float on the morning
tide, when it would be also dark.
I should propose then to stop about 36 feet short of the end.[162]
[Sidenote: _Evening._ Clear away shores of the 20-feet cradles.]
At low water, although dark, I shall endeavour to knock away the
shores of the 20-feet cradles, or as many of them as possible, and
clear all from these cradles except the unbolting of the
filling-pieces.
[Sidenote: Under favourable circumstances clear away also _all_ the
shores on the port side.]
If the operations have proceeded easily, and the ways not sunk
much, I shall also knock away all the long shores on the inshore or
port side of the ship, so as to leave less to do on the following
day.
[Sidenote: Prepare for a further pull at the night’s high water.]
I shall then prepare at leisure to place the barges to get one pull
of 36 feet, or as much more as I can (as I shall not hesitate to
pull the cradles 20 feet off the ways) after high water of that
night.
[Sidenote: Last move at 4 A.M.]
Soon after the high water of that night, and when the water has
fallen sufficiently to prevent any risk of floating, but while the
ship is still waterborne, probably about 4 or half-past 4 A.M., I
shall make the last pull; and although it will be in the dark, yet
having only one pull to make, and plenty of time to prepare, and no
expedition required in the operation, I think it may be easily
done.
[Sidenote: Float on high water, Wednesday afternoon.]
The ship will then be left till low water, when we shall clear away
everything we can from the cradles, and get all ready for floating
at high water on the afternoon of Wednesday.
Provided the mechanical arrangements should prove efficient, the
success of the operation will depend entirely upon the perfect
regularity and absence of all haste or confusion in each stage of
the proceeding and in every department, and to attain this nothing
is more essential than _perfect silence_. I would earnestly
request, therefore, that the most positive orders be given to the
men not to speak a word, and that every endeavour should be made to
prevent a sound being heard, except the simple orders quietly and
deliberately given by those few who will direct.
In a memorandum of ‘Particular Instructions,’ dated the next day,
October 31, there is the following passage:--
_Starting_.--A strain being brought upon all the purchases, and the
holding-back purchase being slack, if the ship does not move, the
two presses will then be worked; if she does not then move, or if,
when moved, she stops and each time requires the presses, the
attempt will be postponed, and more moving power applied for the
next time.
If, after being started by the presses, the river purchases are
found sufficient to move her, the operations will proceed.
In another part of these ‘Instructions’ Mr. Brunel again shows that he
was not, as has sometimes been supposed, under the impression that the
friction would be so small that the only important thing to be thought
of was to check the ship from rushing too fast.
On the contrary, he foresaw the possibility of her not moving at all,
even with the presses, that is to say, with a force of 1,100 tons over
and above the action of gravity. If after moving she stopped, and then
required the presses again to move her, this would show that the
operation could not be properly carried out, and that the work must be
suspended till more motive power was applied. If, again, the river
tackle were sufficient to move her, then the work was to proceed, but
the friction might even then be so great as to render it desirable to
remove all retarding force. He says, in another passage in his
‘Instructions:’--
It is very likely that no checking whatever at the drums will be
found necessary, but that, on the contrary, it will be found
desirable to get rid of any resistance by overhauling the heavy
chains through the sheaves.
The best day on which to begin the launch was Tuesday, November 3, as it
left two or three days of the high full moon spring-tides for the
operations, should they be prolonged.
On Monday, November 2, the chief work remaining to be done was stowing
kentledge or iron ballast on the cradles, to prevent the timbers
floating when the ship should be moved off them. All the appliances were
ready, and, except the river tackle, had been carefully examined. This,
as has been already said, had not been tested.
It was now for Mr. Brunel to consider whether, in consequence of the
river tackle not having been properly tested, he should postpone the
launch till the following month.
It was most important for the Company that the ship should be afloat as
soon as possible; and, as any defects which might exist in the river
tackle would almost certainly declare themselves in the earlier part of
the operation, when nothing worse than delay could be apprehended, Mr.
Brunel, after a careful review of all the circumstances, determined to
attempt the launch.
* * * * *
On the morning of November 3, the work of putting kentledge on to the
cradles was completed by firelight, and the rails were rubbed over with
a mixture of oil and black-lead. All the shores and props which
supported the weight of the ship had been removed, and she was now
resting entirely on the cradles.
Later on in the morning the brakes of the drums were tightened down, and
the dogshores were removed from the ways in front of the cradles. Mr.
Brunel, who had been engaged from an early hour in examining all the
preparations, superintended this operation, and, having satisfied
himself that all was clear and ready, returned to the upper part of the
yard.
By this time it was crowded with people. The Directors, contrary to Mr.
Brunel’s expressed wish, and without informing him of their intention,
had issued a large number of tickets of admission. A few days before,
Mr. Brunel had suggested that four policemen should be obtained,
thinking that all they would have to do would be to contend with
trespassers. The police force actually present were ignorant of the
portions of the yard to be kept clear, and Mr. Brunel had himself to go
and assist in ordering visitors away from the neighbourhood of the path
prepared for the tackle of the stern hauling gear. The crowd soon became
so great that it was almost impossible for the men in charge of the
hauling-engine at the stern to see the signals given from the middle of
the yard, or for those in the middle of the yard to see what was
happening at the stern.
At about half-past 12 o’clock the fastenings of the ship at the bow and
stern were let go, and Mr. Brunel ordered a small amount of slack to be
given off from each drum. This was done by men turning the handles of
the gearing which had been provided for winding the chain on to the
drums. The order was then given to haul on the bow and stern tackle, and
to pump at the hydraulic presses. It is doubtful what amount of strain
was put on by the tackle and the presses, but it was probably not very
great.
Presently a shout from the forward cradle announced that it was moving,
and almost immediately the stern cradle also started with what appeared
to be a considerable speed. The men who had been engaged in turning the
handles of the gearing had remained leaning against them. As soon as the
ship had moved a few inches, she took up all the slack chain. This made
the drum revolve, and the handles of the gearing spun round very
rapidly, striking the men, and throwing them into the air. The men who
were at the brake-handle next to the gearing ran away. Mr. Brunel, who
was standing near the drum when the accident happened, shouted to the
men to hold on to the brakes, and ran to the spot. The men who had
remained at the other brake-handle hauled it down with the tackle. A
great restraining force was thereby brought upon the ship, and her
progress ceased; the forward cradle having moved 3 feet, and the after
cradle 4 feet 3 inches.
Five men were injured. On the death of one of them it was stated at the
inquest, by the foreman of the drum, that, after the slack had been paid
out, he had ordered the men to stand clear. Be this as it may, it cannot
be denied that the handles should not have been used after the securing
chains had been let go; and indeed Mr. Brunel said at the inquest, ‘I
may blame myself, for I did not anticipate that the handles would have
revolved so rapidly.’
After this accident, Mr. Brunel determined to wait till high water
before recommencing the operations. In the meantime the gearing was
removed from both drums.
A more important change was also made in the arrangements. When the ship
moved, the men on the four middle barges became frightened, thinking she
was about to overwhelm them; a rush was made, and one man, jumping into
a small boat, shoved off, leaving the rest to their fate. A report was
at once sent to Mr. Brunel that the men were untrustworthy, and that
they would not remain; and that, as the barges would be of no use
without the men, the chains had better be dropped and the barges
removed. To this Mr. Brunel consented.
It would, however, have been sufficient to take the men off, leaving a
tug-boat and a few steady men to keep the barges out of the way of the
ship; they would then have been available if required. Mr. Brunel, a
short time after he had given the order, ran round the bow with Captain
Harrison to countermand it; but it was too late, as it had been already
acted upon. As events turned out no harm was done, as the centre barges
alone would not have been sufficient to go on with, after the rest of
the tackle failed.
The result of these changes was that when the operations were
recommenced, the only hauling gear was the bow and stern purchases; the
hydraulic presses were also available to start the ship.
At a little after 2 o’clock the signal was given to haul on the bow and
stern tackle, the presses being at the same time pumped up. The brakes
of the drums were slackened, but kept all ready for tightening.
Not long after the strain had been brought on the tackle, several of the
teeth of one of the wheels of the bow steam crab gave way, and the chief
anchor at the stern began to drag, so that no efficient strain could be
obtained. On this being reported, the operations were discontinued; and,
as there was no possibility of getting things ready by the next day, the
launching operations were postponed till December 2, the next full moon
spring-tides.
* * * * *
As soon as this was known the visitors rushed in on the works, crowding
about the cradles and ways; and Mr. Brunel had to postpone those
investigations which he wished to make at once.[163] The whole yard was
thrown into confusion by a struggling mob, and there was nothing to be
done but to see that the ship was properly secured, and to wait till the
following morning.[164]
* * * * *
The next day was devoted to an examination of what had gone wrong, and
to the consideration of what should be altered before another attempt
was made.
At the stern mooring the anchor was bedded into the ground on the
further side of the river.
The difficulty with regard to the four centre barges was got over by
placing the four crabs with their tackles in the yard, on the landward
side of the ship. The four chains attached to the ship, which had before
been hauled on directly from the barges, were now passed round sheaves
on the barges, and brought back under the ship’s bottom to the tackles
in the yard.
The chief alteration, however, was in the arrangement of the hydraulic
presses. On November 3, there were, as has been said, two presses. Two
additional presses were now provided; each of these consisted of two
7-inch cylinders, and was equivalent to a 10-inch press.
With the object of being able to employ the presses continuously during
the descent of the ship, they were arranged to point down the ways at an
inclination of 1 in 12. The four presses were placed one on either side
of the check tackle at the two ways, and were supported by abutments of
timber-work. These abutments each consisted of four rows of piles, one
behind the other at intervals of about 8 feet. The press abutted against
the row of piles nearest to the ship, which were connected by wooden
struts to the piles behind them. Long balks of timber of various lengths
were prepared to transmit the pressure to the cradles.[165]
The four presses might be considered equivalent, at their full power, to
a force of 800 tons; this was so much in excess of the small force that
had moved the ship on November 3, that, even making every allowance for
the advantage of the fresh lubrication in the first instance, it seemed
reasonable to suppose that with this force the ship could be moved down
easily.
* * * * *
As the process of moving the ship with the presses would naturally be a
slow one, Mr. Brunel determined to proceed with the operations as soon
as everything was ready. On November 19 the work was commenced.[166] The
bow tackle was hauled upon first, as the forward cradle was more than a
foot behind the after one, and the men at the forward presses were set
to work. After a short time the timber backing of the presses began to
crack and ‘cry out’; and, without much stress on them, the abutments
were forced back some 3 or 4 inches. The mooring chain of the bow
tackle also gave way, although there was not any excessive strain on it.
On examining the abutments, Mr. Brunel saw the cause of their failure,
and ordered the strain to be taken off. The number of piles was
sufficient, but the way in which the strain was communicated to them did
not enable them to exert the proper amount of resisting power.
This defect was cured by tying the heads of the rearward piles with
bolts to the foremost piles. The ship being secured, each press was
tested to a full strain, and the adequacy of its abutments ascertained.
It was different, however, with the river tackle. The chain which had
parted was an old river mooring-chain of great size. Much delay in
replacing it was caused by dense fogs, which made it almost impossible
to work on the river. Moreover, there seemed a fatality about every
attempt to get a regular trial of any part of the tackle. When, at last,
a trial took place, and a strain was put on, a mooring-chain gave way;
then this had to be fished up from the bottom of the river, and pieced
together, the accident being ascribed to a defective link in the chain.
The trials were, therefore, so few that it was only proved by degrees
that all the regular moorings were worthless; although they had large
chains which ought to have been good for three times the strain put on
them.
* * * * *
The stubbornness of the ship on November 19 gave Mr. Brunel great
anxiety; not from any fear of being unable to apply sufficient power to
move her, but because, on continued consideration of the subject, he
apprehended that a serious difficulty might arise, if there should be a
prolonged delay at a particular part of the ship’s progress.
It has been explained that Mr. Brunel, with a view of obtaining
uniformity of bearing over the surface of the ways, had not attempted to
support them rigidly on piles, but had rested them on the river-bank.
As, however, the foundation of the building slip was comparatively
rigid, he feared lest an unequal subsidence might cause injury to the
ship, if she were stopped for any length of time before she had
completely left the ground on which she was built. He thought that if
the ways sank at this point they would assume a slightly convex form,
and tend to force upwards the flat bottom of the ship. The main part of
the ship’s bottom, between the longitudinal bulkheads, could bend in
slightly under a heavy upward pressure; but this action could not take
place at the transverse bulkheads, as they would not yield without
injury. Mr. Brunel shrank from proceeding with the launch without having
in reserve such an amplitude of power as would prevent the ship’s being
stopped at this critical point. This consideration, together with the
continued failure of the river tackle under such tests as were applied
to it, led him to address the following communication to the
Directors:--
November 26, 1857.
We proved two of the presses yesterday afternoon up to the full
pressure. A third, the largest, was proved partially; it required
some additions, which are nearly completed, and will be in a few
hours. The fourth may, I think, also be relied on to the same
extent, nevertheless, after a careful examination of the effects of
these strains and other circumstances, I have, after a night’s
consideration, come to the conclusion that our means are too
imperfect to justify my moving the ship with them in their present
form. The presses would start the ship, but it is evident that if
required to be used constantly, that is repeatedly, the piles would
become loosened so as to draw and rise; this again might be
remedied by loading, but clumsily, and with other contingencies,
which I will report, combine to render it hazardous to depend upon
them. My original intention, the right one, was to fit up properly
such an hydraulic apparatus as should be fitted to move the ship
the whole length of the ways, and to depend upon the whole river
tackle only in the event of her moving very easily and for getting
her off the ways at the end. From an unwise attempt to economise I
determined to dispense with the immediate costly apparatus for
pushing, and by sufficient power merely to move the ship at
starting or in the event of sticking, and to depend upon the same
river tackle to keep her moving down the ways. The power originally
calculated upon for the river tackle has gradually, step by step,
failed us; the moorings supposed to be sufficient for certain
strains have failed us at one-third of those strains, another has
parted since our last attempt, and, instead of full 350 tons of
power from this source, we cannot now depend upon 200, and this,
added to the inefficiency of the pushing power, would risk the
sticking of the ship, which might occur exactly at a point which
would involve serious difficulty to remedy. I am assuming a
combination of adverse circumstances, perhaps not likely to occur,
but quite possible; and the conclusion I am compelled to come to is
that our apparatus is too defective, and that the original plan of
a proper and sufficient hydraulic apparatus, arranged in a complete
well-constructed mechanical manner, to push the ship continuously
down the ways, ought to have been followed out, and is now the only
mode of doing the work safely, that is, without the risk of being
involved in a difficulty much greater and more costly.
I have only to add that bad as this report of our condition is, it
is at any rate the worst that can be made of it, that nothing
whatever has occurred to show that any new difficulty has arisen or
anything whatever to create any new difficulty. We could move the
ship now if it were wise to do so, but with great doubts whether
our pushing apparatus in its present form, imperfect and
unmechanical, would continue effective if repeatedly used, and the
certainty that our river tackle is far inferior to what is
required, and also of doubtful and more than doubtful permanency
for repeated strains, it would not be right to commence....
Mr. Brunel at the same time determined to obtain, on a large scale, a
measure of the deflection that might be expected from the weight of the
ship coming on the ways. More than 100 tons of kentledge was piled on a
portion of the ways 10 feet square, in such a manner as to give a
pressure thereon of about double that which would be produced by the
weight of the ship.
It was necessary that this test should not be tried on too small a
scale, as a weight resting on an isolated patch would receive support
from the surrounding ground, which it could not of course do if that
ground was equally loaded. The ways sunk so little under the test as
completely to reassure Mr. Brunel, and to show that no serious evil need
be contemplated in the passage of the ship from off the place where she
was built on to the newly made ways, even though she might be again
stopped for some time. He therefore determined to go on at once with the
launching operations.
The result of the test was very satisfactory to him, and it enabled him
to carry on the work with the same confidence as he had at the first
felt--‘that the ship may stop halfway or not move at all ... but no
injury to the ship can result from any failure in the course of
proceeding in this mode of launching.’
Shortly before the second attempt to move the ship, on November 19, the
experimental cradle had been again put up with a view of obtaining some
additional data as to the hauling strain that might be required. The
deductions made from them were the same as those obtained in the
commencement of the year, and encouraged the hope that the motive power
required would not be excessive.[167]
* * * * *
By Saturday, November 28, the four presses had been got ready; and the
river tackle, though still far from being beyond reproach, had been got
into place, and partly tested.
The brakes were eased, and a small amount of slack was overhauled on
the check-tackle chains by the men stationed on the ways for that
purpose. As on the previous occasion, the pressure was to be first put
on the presses at the foremost cradle.
Arrangements were made for promptly following up the ship if she moved
freely. A black board was placed on each cradle for recording the
progress of the ship.
Mr. Brunel stood on a low platform in the centre of the yard, as a
convenient position from which to watch and command the operations. A
little before ten he gave the order to commence pumping, and the men at
the hydraulic presses got to work. When the pressure came on the timber
framing which formed the abutments, there was considerable noise of
creaking and crushing as the several parts subjected to strain came in
to their proper bearing. The men soon changed from the large plunger
handle to the small one which put on the full pressure; the timbers of
the abutments kept on crying out, but it was evident that they were not
yielding as they had done before. Presently, while the noise of the
timber-work was still attracting attention, the man in charge of the
measuring apparatus recorded on his black board a movement of one inch;
the ship was again in motion.
She moved steadily, but slowly, under the force of the presses, at a
rate of about one inch a minute, and as soon as the forward cradle had
been moved about a foot in this way, the presses at the after-ways were
set to work, and the river tackle was put into operation, first the bow
and stern tackle, and then the four middle purchases. All went well with
the presses, but the strain had not been put on long, when the stern
mooring-chain and one of the two chains at the bow broke; an anchor at
the bow had also begun to drag.
Later in the day part of the moorings of the centre barges also gave
way. Captain Harrison set to work to repair these defects as fast as
they occurred; in no way dismayed that, as he was at work remedying one
mishap, the news of another was brought to him. Barges had to be got
into place, the broken ends of cables fished up or under-run and pieced
together, and this often in the dark; for it must be remembered that the
work was going on at the end of November, when the sun rose, invisible
for fog, at half-past seven, and set at half-past four.
With the exception of the river tackle, all had gone well; the presses
and their abutments had acted efficiently, and the ship had been moved
easily down the ways about 14 feet before work was suspended at night.
* * * * *
Though the progress had not been great, there still seemed a reasonable
hope that, by pushing on, the ship might be got down to the bottom of
the ways in time for floating her off at the next spring-tides, namely,
on December 2. Mr. Brunel therefore decided to go on with the operation
on the Sunday. Early in the morning the presses and crabs were again set
to work. The river tackle soon gave way; and, indeed, there was no
reason why it should be superior to that used the day before, as almost
all that could be done in the night was to piece together the broken
chains, and to replace the anchors. The moorings at the bow and stern
began at once to drag, and two of the mooring-chains amidships parted.
The hydraulic presses were then the only available power; and, although
the full pressure was put on, the ship did not move. This was very
disheartening; it was, however, thought that the resistance was due to
some exceptional adhesion. Every effort was therefore made to get
together the means of giving the ship a first start.
It was not till the afternoon that a large number of screw-jacks and
hydraulic jacks which had been procured were got into place; they were
then screwed up hard, and the hydraulic presses being set to work, the
ship began to move in a manner very similar to that of the day before.
There was not, however, much daylight left; and, when night came on, the
distance traversed was only about 8 feet. The comparative facility with
which the ship moved when once started gave hopes that good progress
might be made the next day.
* * * * *
On Monday morning the ship moved without more difficulty than when she
had stopped the evening before, and the work went on quite
satisfactorily. She continued to move slowly, and by dinner-time had
gone about 8½ feet. Three feet an hour was not much, but still if it
could be kept up it would suffice to get the ship down by the next
spring-tides. Arrangements were therefore commenced for lighting up the
ways and pumping machinery, so that the work might be continued through
the night. The repairs of the river tackle were pushed on, the ship’s
anchors, which had just been finished and tested, were laid down for
part of the moorings, and some of the chains were replaced with chains
lent by the Government and by Messrs. Brown and Lenox.
When work was recommenced after dinner the ship made a short slip of
about 7 inches. On pressure being again applied the 10-inch press at the
forward cradle burst. This put an end to all work for the day, and it
was then determined to replace the broken press and to add two more
presses to each cradle, before proceeding with the launch.
* * * * *
The preparations for the new presses were pushed on vigorously, but it
was not till the afternoon of Thursday, December 3, that things were
again ready for a start.
The pumps were set to work and the tackle hauled upon. The ship made
several short slips of a foot or so, and then moved more than 5 feet at
one slide. When darkness set in she had moved about 14 feet, in slips of
greater or less length.[168]
On Friday, December 4, all was ready early, and during the morning
everything went as well as on the day before; but in the afternoon
increased difficulty was found in getting the ship to move, and the
14-inch press at the after cradle burst, as did also a 7-inch cylinder
of one of the coupled presses.
Notwithstanding the delay due to the bursting of the presses, the ship
was moved some 30 feet; but there was no longer any chance of getting
her afloat at the spring-tides, and the increased adhesion gave cause
for the fear that still more power would have to be applied.
* * * * *
On the next day, Saturday, December 5, the ship made a short slip; but,
although the pressure was kept constantly on, no further advance was
made until late in the afternoon. Mr. Brunel then tried suddenly letting
go the strain on the stern tackle. The sudden relief of the side-way
strain on the end of the ship sent a tremor through the hull, which
served to destroy the adhesion, and she slid several inches. This
operation was several times repeated, and although there were a number
of vexatious delays from pushing-pieces giving way and other mishaps,
she was moved by the evening a distance of about 7 feet, the resistance
due to adhesion being very great.
* * * * *
On Sunday some of the presses farthest from the cradles were moved down
the ways nearer to the ship, so as to avoid the necessity of using long
pushing-pieces, which required much attention to prevent their bulging
sideways. The river tackle now consisted of the bow and stern
steam-engine purchases, and two crabs and tackle, one at each end of the
ship. The moorings opposite the centre of the ship having proved
worthless, it was necessary to lay down new moorings, and it was found
more convenient to lay them opposite the ends of the ship.
* * * * *
The next day, Monday the 7th, after the commencement of operations,
considerable delay was caused by the failure of some of the feed pipes
of the presses. These defects were not cured till after dinner-time,
when the operations were resumed, and before dark the ship was moved
about 6 feet.
On the following morning several short slips were made, and the ship had
been moved about 4½ feet; but, at 10 o’clock, a dense fog came on, and
rendered it impossible to proceed. The next day was occupied in
re-arranging the tackle and presses.
* * * * *
These were not ready till the morning of Thursday, December 10; when, on
the presses being again set to work, and one of the chains being as
before suddenly slackened, the ship made one slip of a little over a
foot; but, on the strain being again applied, two of the anchors began
to drag. As it was now essential to have the river tackle, in order by
shaking the ship to destroy the adhesion, and by the drag of the
catenaries to increase the length of the slides, Mr. Brunel determined
to dispense with the anchors, and to attach the chain cables to piles
connected by framework. These abutments or pulling points for the chains
were now constructed on the other side of the river, opposite the bow
and stern of the ship.
* * * * *
The launching operations last described, namely, from December 3 to
December 10, were full of incident. Nor was the scene wanting in that
animation which agreeably interests a bystander, the more so if he is
not thoroughly conversant with the meaning of all he sees and hears, so
that he mistakes a loudly spoken word, loudly spoken merely that it may
be plainly heard, for a prompt and urgent command.
The labourers at the pumps relieved the monotony of their work, and
shook off the cold, by taking a lively and talkative interest in the
progress of the launch, and echoed the orders given them to pump with
the ‘big plunger,’ or ‘little plunger’ of the pumps, or to ‘fleet’ the
press. This and the singing of the gangs, which were constantly at work
moving chains for the repair of the river tackle, or rolling logs of
timber on to the ways to serve as pushing-pieces for the presses, gave
plenty of life to the operations; and then when the pressure had been
got on the presses, and shouts from the bow and stern of the ship passed
the word that the river tackle was hauled taut, the order would be given
to ‘let go’ the chain at one end of the ship. Immediately the rattling
noise announced that this had been done, and, after a second or two of
anxious watching, the ship slid off, the timbers, abutments, and
pushing-pieces creaking and groaning as the strain was suddenly
relieved. While the ship was in motion, the whole of the ground forming
the yard would perceptibly shake, or rather sway, on the discharge of
the power stored up in the presses and their abutments. The appearance
of the ship moving sideways in these short slips, when seen from the
ways, was very imposing.
All these somewhat striking surroundings of the operations were
naturally heightened in effect, when the work was being carried on in
the early morning or late in the afternoon; and when the timber-framing
and the groups of men at work were illuminated by the glare from the
open fires which were kept burning near the pumps and presses.
* * * * *
The preparations already described were not completed till December 15.
In the meantime Mr. Brunel had been joined by his friend Mr. Robert
Stephenson. Mr. Stephenson had not been aware of many vexatious
circumstances which had even prevented Mr. Brunel from making full use
of his own staff of assistants. Mr. Stephenson expressed to a common
friend his regret that Mr. Brunel had not invited him down to the ship,
and said that he should have gone down uninvited, but that he thought
Mr. Brunel had reasons for not wishing it. On the state of affairs being
explained to him, Mr. Stephenson said, ‘I’ll go down to him at once;’ he
did so, and his arrival at Millwall was very welcome to Mr. Brunel.[169]
Mr. Stephenson agreed with Mr. Brunel as to the expediency of
suspending operations until an ample excess of power was applied.
Fortified by the support of Mr. Stephenson, Mr. Brunel was prepared to
advise the Directors to adopt this course; but, as the preparations for
recommencing the work were just completed, it was determined to make a
trial on the afternoon of December 15. The presses were all pumped up,
and the river tackle hauled on; but, although the force applied was at
least 300 or 400 tons greater than that which had last moved her, the
ship did not yield, and the attempt was abandoned. After a careful
consultation on the depressing result of this day’s work, it was
determined to make another attempt the next morning, in order to see if
any new form of difficulty had arisen; and that after this operations
should be suspended, and an ample number of additional presses provided.
* * * * *
The following day, December 16, as soon as Mr. Brunel and Mr. Stephenson
had arrived, the pressure was again put on the presses, and the river
tackle having been hauled taut, the chains at the bow were let go, and,
to the great satisfaction of all present, the ship made a short slide.
The record of her movement showed that, although the adhesion was much
greater, the retarding force of friction was about the same as before,
and that therefore there was no reason to assume the existence of any
special obstacle. Another short slip was made; but, in getting up the
pressure again, a press was burst, and the work was then stopped.[170]
Mr. Brunel’s decision to suspend the launching operations at this point
was approved at a meeting of the principal shareholders held the next
day. His report to the Directors, and a memorandum of a verbal statement
which he made to the meeting, are as follows:--
December 17, 1857.
In my letter of October 23, which was published at the time in the
daily papers, I referred to the possible contingency of the power
provided to move the vessel down the ways proving insufficient, and
the operation then about to be attempted being so far unsuccessful;
and, referring to what I considered a countervailing advantage in
the absence of risk, I stated, ‘the ship may stop half-way, or may
not move at all, more power may have to be applied, but no injury
to the ship can result from any failure in the course of proceeding
in this mode of launching.’
The result has been that after moving the vessel nearly half the
distance to low water, it has become necessary to increase very
considerably the power which has effected this much, although it
had already been much added to during the operation.
This will unavoidably be attended with some expense and delay, but
not considerable, as the requisite hydraulic presses can be
obtained ready made, and their application is simple, and the
result cannot, I apprehend, be doubtful.
I do not mean to imply that I contemplated any such great increase
of resistance as probable, such experiments as could be made before
moving the ship having given me good reason to hope for a different
result; but the possibility of it was contemplated, and I refer to
this merely as explaining the statement I now make, that the
difficulty is simply one of degree, of more or less power being
required, and that nothing whatever has occurred to create any new
class of difficulty. The launching ways, about which anxiety had
been expressed, and not unnaturally, have stood perfectly and
without any settlement or any derangement by being passed over.
There is no change of gradient or inclination in the ways capable
of producing any effect, as has been supposed; the upper part of
the ways having an inclination of 1·025 inches per foot, and the
lower part, where the ship now is, one of 1·000 per foot, a
difference too small to be appreciable, but which possibly by some
mistake of figures may have led to the erroneous impression
referred to.
The amount of resistance upon the ways in their present condition
and inclination has now been positively ascertained, and an ample
excess of power being applied, there can be no reason to doubt the
result. I propose to apply that excess by going considerably beyond
the amount which the calculation founded upon the results actually
obtained would give as the maximum, and to double the power which
has last moved the vessel.
_Memorandum of a verbal Report made to the Directors, and a small
Meeting of the Principal Proprietors._
December 17, 1857.
That after full consideration of all the circumstances, and
assisted by the best advice I could call in to my aid, namely, that
of my friend Mr. Robert Stephenson, I considered that the only mode
of proceeding, and one which there appeared no reason to doubt
would succeed, was to apply considerably more press power; that I
proposed to double what we had; that I believed I was able to put
my hands upon the requisite presses; that the river tackle so far
as it went might now be considered good, but that unfortunately we
were obliged to take up the principal part of the chains, which
with great kindness and liberality Messrs. Brown and Lenox had lent
us, and were now peremptorily called upon to deliver up; but that
with their assistance I could replace them....
A large number of presses were obtained, the owners for the most part
lending them free of charge. Among these presses was the large one, with
a 20-inch cylinder, which had been used for lifting the tubes of the
Britannia Bridge.
On each of the ways were placed nine presses. The total sectional area
of the cylinders at the forward cradle was 1,066 circular inches, and
that of the cylinders at the after cradle was 1,358 circular inches;
but the Britannia press was not to be worked to its full power, so the
total area of the cylinders may be taken as 2,300 circular inches, or
1,800 square inches. The presses might be considered as good for at
least 2½ tons on the square inch; this gave a power of 4,500 tons,
which, with the 1,000 tons due to gravity, gave 5,500 tons, or equal to
nearly half the weight of the ship. The presses were now coupled
together in groups, in order to ensure that an equal pressure should be
brought on them; and to each of these groups an accurate pressure gauge
was attached.
* * * * *
All the presses having been tested, it was determined to recommence the
actual operation of launching on Tuesday, January 5.
So much of the water in the pipes had been frozen that it was eleven
o’clock before the order was given to the men to pump. When at one group
after another the pressure was shown to be one ton on the circular inch,
the pumps were stopped. As the backing of the presses continued to yield
slightly, a stroke or two of the handles had to be made from time to
time, to keep up the required strain. For six minutes there was perfect
silence, and then the ship moved, sliding down about 3 inches.
The same process was repeated at the stern cradle once or twice, and
then at both cradles. After this the order was given that the pumps
should be kept going till she moved. This was accordingly done, and when
the pressure amounted to 1¼ ton on the circular inch the ship made a
slide of about 4 inches. In this manner she was moved about 5 feet
before work was stopped in the evening.[171]
On January 6, there was a singular change in the behaviour of the ship.
During the whole of the forenoon she moved gradually, yielding to the
pressure at a rate of about an inch in four minutes. In the afternoon,
however, she moved in short slides.
During this and the three following days her progress was about 10 feet
each day. After this the ship, being to a considerable extent
waterborne, was moved with greater ease, and on Tuesday, January 12, 20
feet was accomplished in less than four hours.
* * * * *
By Thursday, the 14th, the ship had traversed a distance of 197 feet at
the forward cradle, and 207 feet at the after cradle. It was thought
unwise to advance further till the coming spring-tides on the 19th of
the month were past, lest an exceptionally high tide might come
unexpectedly, and partially float her. As soon as the spring-tides had
passed, she was moved on cautiously, a short distance at a time, and the
depression of the ways was carefully observed. This was found to be
inconsiderable, and the cradles were gradually pushed 25 feet off the
ways. As the spring-tides came on, water was run into the ship, to
prevent her from floating prematurely.
* * * * *
The upright struts of the cradle on the side next to the river were all
removed, and the wedge-pieces had chains fastened to them, with the ends
brought on deck; so that, if any of the wedge-pieces got jammed and did
not come out when the ship floated, they might be hauled out by the
chains.
The river tackle now consisted of two purchases at the bow and two at
the stern. To keep the ship, when she floated, from being drifted by
the tide or wind, chains were carried from the bow and stern to
moorings, by which her movement up and down stream might be regulated.
Four tugs were in attendance to tow the ship to her berth, and a
floating fire-engine was also ready to pump water into her, should this
be necessary owing to any sudden postponement of the launch.
Nothing now remained but to watch carefully for a suitable tide.
* * * * *
It was determined that, if the weather were favourable, the floating
should be effected on Saturday, January 30. The tides had been below the
average, and on the Friday matters did not look promising; the tides had
continued low, and the weather was bad. A careful watch was kept on the
tide, observations being taken every half hour, and plotted on a diagram
so as to show at a glance the probable height to which it would rise.
The tides showed signs of improvement, and they commenced to pump water
out of the ship on Friday night; but, as time went on, the weather did
not mend, and the wind was blowing from the south-west against her
broadside; therefore in the early morning Mr. Brunel, who was in person
attending each turn of affairs, ordered water to be pumped in by the
fire-engine. There was hard rain and strong wind; and telegrams which,
according to arrangement, were being frequently sent from Liverpool and
Plymouth, showed similar weather. This continued throughout the
Saturday, and the tide was low; but, when it began to rise in the
evening, it gave indications of being a very high one. As soon as the
tide reached the Kingston valves, Mr. Brunel had water run into the
ship. Although she rested uneasily on the cradles, she remained safely
in her position.
In the evening the rain came down in torrents; nevertheless, after
midnight the weather mended, and the wind went round to the north-east.
As the telegraph gave the same report from Liverpool, Mr. Brunel,
encouraged by every sign of fine weather, and having the good promise
given by the high tide of the night before, determined early on the
morning of Sunday, January 31, to float the ship on that day.
The pumps were immediately started to discharge the water from the ship.
The bolts securing the wedge-pieces of the cradles were unfastened at
daybreak, and the ship was then ready.
The morning broke with great splendour after the gloom of the previous
days, and the tide, as soon as it had turned, began to rise with unusual
rapidity. It had been arranged that all the men should be at their posts
at the presses and crabs by eleven o’clock; but the tide was not only
very high, but exceptionally early; and, although a considerable margin
had been allowed, it was not sufficient. Mr. Brunel and his assistants
hurried the men to their places, the presses were set to work, and the
ship was put in motion down the ways for the last time.
At a little before one o’clock observations taken by levels showed that
the ship had ceased to descend, although she was still being pushed
forward. Shortly afterwards Captain Harrison, who had gone on board,
sent Mr. Brunel word that all the wedge-pieces had floated up on the
outer side of the ship; and at twenty minutes past one the stern was
seen to be afloat. Mr. Brunel had been loath to haul out the ship by the
river tackle, lest the wedge-pieces might get jammed; but, as soon as he
was informed that they had floated up, he sent orders for a strain to be
put on the bow tackle. This was at once done, and by twenty minutes to
two the bow rose from the cradle.
Mr. Brunel then ordered the checking gear to be secured, that the ship
might be sooner hauled clear of the cradles, and he went on board. He
had scarcely done so when a serious difficulty arose. It has been
already said, that in order to keep the ship from moving up or down
stream, cables had been carried out to moorings ahead and astern; and
both these chains had been hauled up tolerably taut, at least the slack
had been taken out of them, so that if required they might be at once
available. Now when Mr. Brunel had given the order for the bow out-haul
tackle to be hauled upon, Captain Harrison, in order to supplement it,
ordered the tug-boats to haul the bow off. This order was by some one
conceived to have been given with the object of hauling the ship ahead;
and to facilitate this the stern mooring-chain was let go.
By this time, though the tide was still running up the river, its
strength was much diminished; and the drag of the chain at the bow of
the ship was sufficient to pull her forward against the tide. The
paddlewheel on the shore side then came in contact with the upright
timbers of the forward cradle. Mr. Brunel ran down from the ship into a
boat and examined the place where the wheel was fouled. He then hurried
back on board, where, as through some blunder the stern outhaul had also
been let go, he had now little but the tug-boats to depend upon. They
were of course of but small value for a dead pull as compared with the
chain tackle. He had the bow chain veered out and the tugs all set to
work, assisted by the tide, to haul the ship up the river.
In about twenty minutes time, the paddlewheel was got clear of the
cradle, and this great difficulty was overcome. Fortunately, the tide
was an extraordinarily high one, and the time of available high water
was long.
* * * * *
The ship had not been moved far towards her berth when another mishap
delayed her progress. The barge of the bow purchase came foul of the
starboard paddlewheel, and the only way of freeing the ship was to
scuttle the barge. When this was done it sank away clear of the wheel,
and the ship proceeded to her berth on the Deptford side of the
river.[172]
* * * * *
By about seven o’clock she was safely moored; and the cheers of the men,
as Mr. Brunel went down her side, announced that the launch of the
‘Great Eastern’ was at length accomplished.
NOTE A (pp. 348, 368, 372).
_Experiments and Observations on Friction._
In January 1857, Mr. Brunel took steps to form an estimate of the
amount of hauling or of retarding force that would probably be
required in the launch.
Two rails were laid at an inclination of 1 in 12, and upon them an
experimental cradle was placed, with three cross-bars similar to
those which were to form the under surface of the cradles. The
three cross-bars therefore made six intersections on the two rails,
and the small cradle was loaded with about 8 tons, so that the
weight on each intersection was about equal to that which would
come on each of the intersections of the actual cradle. This
arrangement was not therefore a model, but a correct representation
of a part of the cradles, and which might, with an exception to be
noted presently, be taken to exactly represent, by its conduct, the
conduct of every similar part of the actual cradles. Experiments
were made with one or two kinds of unguents, and, what was a more
correct representation of what was likely to occur, with the rails
and bars clean but not bright, and without lubrication.
The experiments with lubrication were useful rather as comparing
the various lubricants one with another than as representing, by a
mere process of multiplication, what would be the behaviour of the
ship on her cradles, because, for the reason already pointed out in
the case of wooden sliding-surfaces, the lubrication would be more
and more rubbed away as more of the cradle passed over it; thus the
experimental cradle, when tried with lubrication, represented
rather the behaviour of the front part of the cradle than that of
the whole. Had the ship herself been moved uninterruptedly down the
ways, the state of things would have been something between good
lubrication and none at all. As the under sides of the bars were
lubricated, any motion of one end of the ship before the other
would tend to move the bars sideways over the rails, and so to
spread the lubrication, and to pick it up and re-deposit it. Mr.
Brunel thought but little of the black-leading of the ways,
considering that it would be rubbed off by the leading bars of the
cradles; but a very little lubrication on metal surfaces is
sufficient; and doubtless, had the ship been moved continuously
down the ways, considerable assistance would have been derived from
the lubrication which was applied.
The results of the experiment were curious. The generally received
notion is, that friction between rubbing surfaces is independent of
the velocity; that is to say, that whether a body be moving fast or
slow within reasonable limits, the retardation due to friction is
the same; that if a body be sliding at a given velocity, whether
that velocity be great or small, a drag of a certain number of
pounds will keep it moving at that velocity. It was, however,
always understood that a greater force was necessary to start a
body from rest, to overcome adhesion. The experiments made with the
experimental cradle distinctly showed that any rule as to friction
being constant at different velocities was untrue. It was evident
that, as the speed increased, the power required to overcome the
friction became less. No exact records are extant of the
experiments made with this experimental cradle before the launch;
they were, however, repeated during the launch with great care, and
the results very carefully analysed. The experiments showed
generally that the tractive force, including the action of gravity,
was never more than ⅛, or less than 1/15, of the weight.
Although the experiments showed that the amount of friction in the
case of the actual launch would lie between the limits above
mentioned, they at the same time indicated that it would not
probably approach either of those limits.
* * * * *
Shortly after the commencement of the launch, Mr. Brunel had the
experimental cradle and ways re-erected. A very simple arrangement
was fitted up, by which the forces at work at each period of the
progress of the cradle in each experiment might be deduced. The
results of these experiments, which, as may be supposed, were
similar to those obtained in the commencement of the year, were
most instructive; they showed quantitatively the decided diminution
in friction which took place as the velocity increased, and the
amount of that diminution. The apparatus was very simple. The
experimental cradle, which has already been described, was made to
slide down its ways by a chain attached to a suspended weight. The
weight employed was generally about 5 cwt. After the cradle had run
a certain distance, the weight reached the ground and the cradle
proceeded with the momentum it had obtained. The velocity given to
the cradle down the ways was measured in the following manner. A
long piece of tape was coiled round a reel placed at the top of the
inclined rails or experimental ways, so that it could revolve
freely and pay out the tape as required. One end of this tape was
attached to the cradle, so as to be drawn after it as it ran down
the rails. The tape, as it ran off the reel, passed over a guiding
board over which swung transversely a pendulum arranged to swing
once every quarter of a second. At the lower end of this pendulum
was attached a brush which was filled with paint; and as soon as
the model cradle moved, the pendulum was set oscillating by a
self-acting trigger arrangement. The pendulum in its oscillations
made marks on the tape as it ran out at every quarter of a second
of time. Thus, by an examination of the tape, could be determined
the exact distance which had been passed over by the cradle during
each quarter of a second of the time during which it was moving.
The rate of progress being thus known, and the actuating force
(gravity acting on the cradle and on the suspended weight) being
also known, it will be understood that the exact amount of the
resisting force, namely, friction, could be calculated exactly, and
this for each moment and position of the descent of the
experimental cradle.
The following results of these experiments were recorded in terms
of the corresponding amounts of tractive force that would be
required to produce similar results in the case of the ship and
cradles, a weight of 12,000 tons.
+------------------------------+-----------------------------+
| | Force in tons required |
| | to move or restrain ship on |
| | incline of 1 in 12 |
+------------------------------+---+------+---+--+---+-------+
|Velocity, feet per second | 0 |0 to 1|·75| 1|1·5| 2 to 3|
+------------------------------+---+------+---+--+---+-------+
| RAILS AND CRADLE BARS. | | | | | |Retard-|
| | | | | | | ing |
| | | | | | |{ 110 |
|No. 1. Ample lubrication | | .. | ..|60| 0 |{ to |
| | | | | | |{ 200 |
|No. 2. Medium lubrication | | 120 | ..|..| 0 | 60 |
|No. 3. Very little lubrication|400| |200|..| 0 | .. |
| {| | 560 | | | | |
|No. 4. No lubrication {| | to | ..|..| 0 | .. |
| {| | 400 | | | | |
+------------------------------+---+------+---+--+---+-------+
+------------------------------+--------------------------------------+
| | Force in tons required to move |
| | a weight equal to the ship on |
| | similar ways, but on the level |
+------------------------------+-----+------+-----+-----+-----+-------+
|Velocity, feet per second | 0 |0 to 1| ·75 | 1 | 1·5 | 2 to 3|
+------------------------------+-----+------+-----+-----+-----+-------+
| RAILS AND CRADLE BARS. | | | | | | |
| | | | | | | |
| | | | | | |{ 890 |
|No. 1. Ample lubrication | | .. | .. |1,060|1,000|{ to |
| | | | | | |{ 800 |
|No. 2. Medium lubrication | | 1,220| .. | .. |1,000| 940 |
|No. 3. Very little lubrication|1,400| .. |1,200| .. |1,000| .. |
| {| | 1,560| | | | |
|No. 4. No lubrication {| | to | .. | .. |1,000| .. |
| {| | 1,400| | | | |
+------------------------------+-----+------+-----+-----+-----+-------+
In every case where a velocity approaching to 3 feet per second was
attained, whether the ways were lubricated or were quite dry, the
model, though there was no tractive force acting on it other than
that of gravity down the incline of 1 in 12, rapidly increased its
speed till it reached the end of the ways.
These experiments are worthy of note for the contradiction, already
referred to, which they gave to the received rules relative to
friction. It will be seen by these experiments, and as will
hereinafter appear from the results of the movements of the ship
herself during the launch, that with different degrees of velocity
very great variation in the friction was apparent, amounting to a
difference of about thirty per cent. in the case of unlubricated
surfaces, according as the velocity was nearly _nil_ or was 1·5
feet per second, which is a comparatively small velocity. The
friction in this case was, on a weight of 12,000 tons, 1,500 tons
at a very low velocity, and but 1,000 tons at a velocity of 1·5
feet a second or about one mile an hour, the friction at the very
low velocity being fifty per cent. greater than that at one mile an
hour.
As soon as the ship began to move by slides, the recording
apparatus of tape and pendulum was applied to record the nature of
the ship’s movements. This apparatus was similar to that already
described. The tape was attached to the bottom of the ship under
her centre of gravity, and recorded the rate of retardation of the
ship when left to herself after the motive appliances had, with the
exception of gravity, ceased to act; and the amount of friction
acting to retard the ship was determined with a very considerable
amount of accuracy.
The best experiments made were on December 7, 8, and 10; and the
results are very interesting. The dirt and rust of the sliding
surfaces had increased the adhesion very much, and a considerable
force was necessary to start the ship. There being no good pressure
gauges to the presses, it was impossible to decide exactly what was
the force required to start the ship, for of course the tape record
gave no information on this point; but there is no doubt it was
considerable, probably 800 or 1,000 tons in addition to gravity,
and was thus far greater than the force to start that had been
observed with the experimental cradle.
But the remarkable fact was that, notwithstanding the deterioration
of the sliding-surfaces as evinced in the increased difficulty in
starting, the friction, when once motion was established, was
proved not to be very largely in excess of that which had been
exhibited in the experiments.
In the various experiments tried, it was shown that when the ship
had a velocity of between 6 and 8 inches per second, the amount of
friction was only about 100 tons in excess of the action of gravity
down the incline; while as the velocity became less, the friction
became greater, till, as the velocity became smaller, the friction
increased from 200 to 300 tons in excess of the action of gravity.
The results obtained by the observations made on the motion of the
ship having shown that its behaviour when in motion accorded with
that of the experimental cradle, there is every reason to believe
that if the ship had ever attained a velocity of 1½ to 2 feet per
second, which might have happened had the river tackle acted well,
the friction would, as in the experimental cradle, have become less
than the action of gravity down the slope, and the brakes would
have had to be employed to check the motion.
NOTE B (p. 384).
_Letter from Mr. Brunel to W. Froude, Esq._
February 2, 1858.
My dear Froude,--It is no news to you to tell you that we have
floated, but still you will perhaps feel sympathetically some
pleasure in hearing of it from me, as I do in writing to you upon
it.
We have in fact gone on well and without mishap since we have
resumed operations with plenty of power; we have not gone very
quickly because our jumps have been small, or we have gone by a
continuous motion--we have had a great deal of this, and all the
last 30 or 40 feet I think, or more, has been so, the power being
_with_ gravity about a quarter of the weight, sometimes
less--occasionally, when the water was high, considerably
less--buoyancy being of course taken duly into the calculation.
Once, when still weighing fully 3,500 tons, and with 1,200 tons of
water in her, making 4,700, less some buoyancy of the cradle, she
moved so easily that they came running to me from the other cradle,
to say that she was moving of herself, and asking what to do.
She certainly had not much more pressure on than we had assumed to
be necessary to overcome all the friction of thrust timbers, &c.,
certainly could not have had above 300 tons of real push to move
2,000
2,000 tons, 2,000 -- ----- (gravity) = 1,833 tons.
12
I think that when the load became much lighter on the rails, that
the mud and even the sand of the Thames form a lubricator and
_rollers_ which offered less resistance than the dry rail, or the
rail with pressure enough to displace the mud or imbed the sand.
Having at last pushed the cradles beyond the rail, and found her
stand well, and moved a few feet more and still stand upright, I
waited for a tide, and arranged a good communication with
Liverpool and Plymouth to telegraph up wind and weather, morning
and night, so as to help in foreseeing a tide.
On Friday morning, at 3 A.M., the tide began to improve, but the
wind was still in the wrong quarter for a good tide, and as I think
I have told you the tides of this month, and of the whole year of
‘58, are very poor. Besides this, it blew a gale. I therefore began
pumping out the water, but stopped at 1,200 tons, and at 10 A.M.,
seeing no improvement in the weather, I filled in by the
fire-engine about 1,300 or 1,400 more, and gave up the attempt, and
very fortunately, as the tide did not rise high enough, and the
wind right on her broadside increased.
On Saturday night things grew worse, and the wind at Liverpool and
Falmouth finished in the evening still SSW. About midnight the wind
lulled, the rain came down in torrents; the wind gradually stole
round to the northward, and the tide came rolling up uncomfortably
quick. I admitted water as soon as it would run in, and only just
prevented her floating; when, if she had, we should have been in a
mess, as our wedge-pieces were not yet unbolted from the bottom,
nor could we in the night have managed the floating, even if all
had been ready, which nothing was. Under these circumstances, the
wedge-piece being bolted was perhaps our security, as she all but
floated; the stern rose 3 inches though we had 3,000 tons of water
in her, the tide rose so high; we began pumping immediately on the
turn of tide, and by half-past 6 A.M. the wind was gentle from the
NNE., and telegraphs came to announce the same in Liverpool, &c. I
therefore determined upon floating.
We pumped away, and at 10 A.M. cleared everything away, and began
our preparations. I had fixed 12 o’clock to begin forcing her
further down, thinking half-past 12 would have been as early as she
would have moved easily, but the tide came rushing up an hour and a
half before its time; and, although I hurried the men to their
posts, we were rather caught napping. The instant we began
pressing, she moved easily, and by a quarter past 1 we had pushed
her centre past the ways, and she began lifting with the tide.
I had a centre station with a chalk board, giving me the curve of
the tide, and two good levels reading off her stem and stern water
marks. Our calculations had proved very correct. In the skew
position I had pushed her to, she began lifting at the stern first,
as she ought to have done, and her bows soon followed the example.
We stopped pushing the cradles, made them fast, and began hauling
out the ship--she moved very slowly of course.
When she began to move out, our first difficulty occurred by a
little mismanagement, or over confidence, on board; our stern chain
was let go, and she forged ahead against the tide by the elastic
strain of the bow chain, and _I think_ also by the tug-boats
pulling too much, which ought not to have been done, and in going
ahead her port paddles caught hold of some cradle timber rising,
with long 2½ inch bolts holding them to the bottom of cradle. No
tug power would have had any effect upon them. But we had two hours
before us, with a promise of an unusual tide; I hurried on board,
and we succeeded in about twenty minutes in getting a little astern
a little out, and getting clear.
We had some mishaps after this, such as fouling one of our barges,
getting it jammed under the paddlewheels, and the barge fast by the
chain tackle dropt overboard. However, we scuttled and sunk the
barge, and got safely across. We had an extraordinary tide, and
several assistances from nature to counteract any of our own
bungling, and got safely across, and she is now moored in her right
place.
Yours faithfully,
I. K. BRUNEL.
William Froude, Esq.