Sydney Morning Herald (NSW : 1842 - 1954), Wednesday 18 March 1874, page 3


DRY DOCKS. :

THE subjoined report on this subject was presented to the Legislative Assembly on Tuesday by the Hon. John

Sutherland :

Inattention to Mr Secretary Sutherland's directions that I should furnish him with a report on the subject of docks genei ally, as bearing upon the proposal submitted by Government to Parliament to construct a new first-class dock at Cockatoo Island, which would be capable of taking in the largest class of ships, I have the honour to lay before him the following; short report upon the subject, Illustrated by a few sketches of the different kinds of docks which have been brought into use tram time to

time at other places.

Var long methods have been had recourse to for cleaning and repairing the immersed parts of boats and vessels. In early times they were probably hauled up On the beach for this purpose, or, in situations where there was sufficient rise and fall of tide, they were placed at high water on the beach, where the receding tide would leave them high and dry; but as the requirements of navigation demanded the employ most of larger vessels, different and less simple methods had to be resorted to. Careening 01 heaving down, forming gridirons on the flat shore, where the rise and fall of tide was sufficient, graving docks, and patent slips, balance docks, sectional docks, and hydraulic lifts have been tried, where the circumstances seemed to favour each particular plan; and it is worthy of remark that in this harbour are to be found examples of nearly all these different appliances.

Careening-a practice now nearly obsolete was brought to a considerable degree of perfection by the Dutch towards the end of the last century, and was also extensively practised in the French arsenals as well as in those of England. It was performed in one or other of the following ways fire vessel to be examined having first been partly lightened, as much of the cargo or ballast as was considered safe was moved to one side, causing her to heel over, and exposing to view a considerable portion of the other side, which could then be cleaned, caulked, or repaired. This was, however, a dangerous practice, as was shown by the capitching and foundering of the Royal George, at Spithead, in

August, 1782) with Admiral Kempcmeldt and his whole crew of

eCO mm.

In addition to the danger attending this method of careening, there was also the objection that It was frequently attended by a distortion of the shape of the ship, which was caused by the unequal stress brought on the exposed side of the rebel during the operation, and which was rendered permanent by the driving

of caulking into the seams.

Cuterning or heaving down was also performed by bringing the vessel alongside another vessel or wharf, whereon surface of capstans and other appliances had been provided, and, by means of ropes or tackles fastened to the masts, heaving her down to one side until the other side was clear of the water, in which position she was secured while being repaired or coppered ; the operation being then repeated for the other side

In Mossman's Bay are still to be seen thc~whtrfs. with the remains of capstans and other appliances of the heaving down establishment formerly carried on there by Captain Mossman, who gavehiBname to the place. In the early times and indeed for many years after its settlement, this was the only repairing establishment In this colony; but as its trade advanced, and the requirements of the port increased, it fell into disuse and came to be succeeded by the other, and more perfect methods adopted in

the present day.

The ordinary " dry " or " graving docks " as they are generally designated the latter name being supposed to be derived from the French word craze, which signifies a fUt beach or shore these docks being generally formed in such positions are of a very ancient date. From a mere excavation in the river's bank, open to the tide, and occasionally lined with timber to support the soft earth, to the granite docks introduced by the late Mr. Bernie, the change has been gradual and progressive; as has also been the advance from the wooden floating docks which were found on the Thames and dee where about shelf ginning of the present century, to the large Iron floating docks of Larthugena and Ferrol, in later times, designed

by another member of the same distinguished family of engineers.

As far back as 1823 there was a graving dock at Deptford, and in 1867 there was another at Rocheford for the repair, of the French ships of war. Since then they have been constructed in almost every important port of Great Britain, France, and America, where the formation of the ground or the character of

the soil was suitable for such works.

There are, however, many situations where, owing to the occurrence of unsuitable soils, such as quicksands mud, peat, or gravel of great depths, and charged with water, or rock much fissured or disturbed, the construction of dry docks of quarry is difficult and expensive. Of this a striking example is to be found in the history of the United States Dry Dock at New York. In other situations where the ground is suitable, as is the case at

Liverpool and Birkenhead, and markedly so in this port, I their construction becomes almost reduced to a simple question of excavation. At Liverpool, the old red sandstone formation in which the docks are excavated, being perfectly homogeneous, and almost free from water, very little more was required than the mere scooping out of the dock to the required form and building the pier heads ; the great rise and fall of the tide in the River 1 Mersey rendering pumping almost unnecessary. I

Is Part Jackson, a*regards theformellon of the rock, the operation of dock excavation is equally simple, that sandstone hard haine 419 assisted ladU-tnmkakfjt-UMi* tfcersaaUMWM

at Liverf ool ; but. In consequence of the small rise and fall of the ' tide, which is only from 4 to s lect, pumping machinery to em in the duck is required ji. ,u.

The it inquiries which I have referred to us being found in the 0 instruction of masonry ducks in some situations, to with and the extent of pressure of the water, and be perfectly was enough all lines, and which shall also be able to sustain the weight' of heavy ships upon the block has led to the invention of many ingenious substitutes-, a few of which, and the poor land is of the circumstances which have led to their adoption, I shall now

endeavour to describe.

FioATivo DOCKS

The earliest examples of the young ducks somewhat resembled Uvgo boxes, with dates to the open ends, watch on being closet to d he stocks pumped out gave access to the bottoms of the vet is in them TIRBO docks were very common in former years on the I homes, at Portsinou h, and at most of the ducks d cttablishmeniB and they are still employed in some of the French por s A dock of his description may be seen in this her hour at point where it has been won kid wash camp one success for rest are, and where it has proved itself to be a most valuable

part men ion 1

he balance docks and sections docks constructed of timber, which are improvements by Mr Gilbert, (the U S Navy, on the box floating dock last described, have been principally used in America The sectional duck is composed of a number of pontoon said of mines, capable of being ruined tug the , as many lies tons being used as may be required to e. the size of the vessel to be lifted Each season consists of a watertight rectangular wooden box or pontoon, secured to which are vertical frames supporting watertight boxes, which slide up and down, and can be fixed at any desired height by means of a racketeer motion Too oompto o duct thus equals a of tight (H) ten (IO), it as many more independent sections or pontoons as may be required, each one having its two mivable air chambers secured within the frames, one on each side The Philadelphia Sectional Duck consists of nine sets his or pontoons, inch 115 feet in length by 32 feet in width and 16 feet deep When united, they constitute a duck floor of 3 6 feet long and 16 in wide. The total displacement when drawing 16 feet of water is 4500 tons The total cost of the book is stated to have been about £170 000, - a large sum for a s quote e of so perishable a material as wood, of which it is built, These pontoons and air chambers however, being to a great extent independent of one another, neither is able to auppo t the adjoining ours, which is undoubtedly a great objection to ducts of this description, and is stated to have been the cause of the destruction of that at Callao, on which, while a ship was being Hate I, in consequence of some of the bones being lowered I too quickly, the ship's keel pot off the blocks, and she bede I over an Bank, with the dock. Serious damage was also sustains by the dan frun-ci, co dock and H M B. Terangan! nearly capsized while being g listed on it. A floating pontoon of similar kind capsized and tank in the London Docks, a nearly similar accident happened to the dock constructed for Sourabaya, and the large dock erected at Rio was found to be utterly useless The at

Thomas' Dock, constructed of iron, also sank, and remained for some years at the bottom of the harbour, it has, however, been lately raised, and is now in use. In con- quence of these and same other accidents these docks have lately come to be regarded with

distrust.

Sectional docks are sometimes used in connection with patent slip?, the vessel after having been ruined by the pontoons being hauled from them on to a patent slip, when the duck becomes available for other shipS

An illustration of the United States Government Dock at Pctladelphia of this kind is given

q he bsUnce docks, also mainly the invention of Mr Gilbert, are a great improvement on the sectional docks, both as regards the safety of the vessels on them, and of the docks themselves. They are to be found in most of the dockyards of the United States, when they are worked with great BOOCCBS

The United States Government attaching considerable importance to buying their ships of war on. of water and under cover when laid up in a dinner), the docks of Pensacola and Portsmouth, and other ports in the United States, are so arranged that the pontoons on which the vessels are written are brought close to the slipways, on which the vessels can be drawn These slips are of the usual form of construction The di tensions of the Pensacola Dock are-length 350 feet, breadth 17 feet 4 inches, deep h.38 feet 8 Inches Its coat is stated to have been as follows Floating dock, £11 10; buln and slipway, £70, 615 , caisson, £2600, total, £184, 385

In 1858 the Austrian Government employed Mr Gilbert to construct a dock of this kind for the dockyard establishment of Pola the character of the rock adjoining the arsenal being such as to preclude all prospect of const feelings graving dock of the ordi-tary kind, except at a very great cost The dock was built at Venice, and was towed to Pola, where it has since been worked with success In connection with the floating dock there are th'colines of slipway to receive the ships off the docks, when laid up for extensive repairs, the dock being thus left unoccupied i so as to be able to receive other vessels and place them in turn on

the other ships some very heavy Ships have been raised on the

dock, the line-of-battle ship Kaisc , of 3125 tons, the iron-clad, Max, of 366 tons, and the Don Juan d'Austria, of 2128 tons, and 1 many others, having been successfully raised on it and repaired

The mode of working this dock is as follows -The d jen being I moored in a sheltered and secure basin, in about 40 feet water,

and sunk to the required depth by admitting water into the

bottom compartment, the ship to be repaired is 11 rated in, the water is then pumped out by steam power and the dock uses carrying the ship with it till the surface of the lower compart-ment is clear of the water , the dock ia then call ed into shallow basin and grounded at the end of one of the lines of railway, which are UV feet in length, and rise with an inclination of about 6 inches in the 100 feet Each line of rails would hold two firstclass men-of-war or a greater number of small vessels lot absence of tide in the Adriatic, and the completely landlocked character of the harbour of Pola, afforded peculiar facilities for the working of a floating dock of this description.

Carihagesa and Ferrol Docks The Spanish Government having likewise found that there would be great difficulty in con. Btruciiog stone graving docks at their naval arsenals of Carthagena and Ferrol, consulted Mr Rennie in reference to the construction of floating docks which should be capable of lifting their ironclad ships, the weight of which would be from 5000 to 6000 tons They were accordingly constructed, one for Carthagena and a somewhat larger one for Ferrol, of the following dimensions -

Carthagena. Ferrol.

Length... 324 feet 350 feet. Breadth ... 105 5 105 " Height (outside) . . 48 " 50 "

The lifting chamber of the Carthagena Dock is 324 feet long, that of recent 856 feet They are 155 feet broad in both cases and 11 feet 6 inches and 12 feet 6 inches deep respectively

Both docks are constructed of iron plates, and are divided by a number of longitudinal and transverse bulkheads in the former there being twenty and in the latter twenty-two watertight com-partments, by which means the stability of the structure is insured and 11 flotation regulated with the utmost accuracy. The water is admitted to any or all the compartments when it is desired o to ink the dock for the reception of a vessel, and is pumped out by means of the ordinary pumping machinery when it is desired to raise it. The basin at Carthagena, wherein the dock In moored, measures about 1800 feet in length by £120 fee. is wld h, and has

been excavated by dredging machinery to a uniform depth of about 50 feet At the south-west corner of this buln another shallow basin or dock has been constructed to receive the floating dock. This latter basin is of a uniform depth of 16 feet 6 inches, and is 38 J feet in length on the north and 845 feet on the south side, the inner end being curved to a ? adina of 320 feet where the end of the dock, when in place, joins the slips, which i advance in three horizontal lines from the deck, so that after the dock has been grounded in the basin opposite to either of the lines of way the ship to be repaired may be drawn at once on to the slips, thus relieving the d kick, which may then be floated out, and kept in readiness to receive another vessel. The slips are 725 feet in length, 45 feet broad, and are constructed

with altars similar to those in the ordinary d necks, to admit of the ships being securely stored upon them Each ship will hold two first-class, or a greater number of smaller vessels

The accompanying sketch of the Carthagena dock, which shows a ship undergoing repairs in it, will illustrate the design and afford some idea of the general construction and mode of working it and the slips The shallow basin in which the dock is grounded may be closed by means of a caisson and the water pumped out,

should it be necessary to repair or paint the dock Itself. The

weight of the Carthagena Dock is 4400 tons, and its cost was about £160,000, exclusively of she cost of the brain, slips caisson, and other appliances, which would probably bring the whole cost up to about £350,1,00 The Spanish iron-clad ship Numancla, weighing over 5000 tons, and other ships of the same class, have been lifted on it and rep tired with perfect safety

Callao Floating Dock - An iron floating dock, similar in most respects to that just described was constructed and sea

to Callao. Its principal dimensions are-total length, 300 feet, breadth over all 100 feet, w iden inside, 76 feet, depth, 30 feet, width on floor, 50 feet, depth of bottom compartment, 12 feet This dock is represented on the accompanying sketch, which gives a perspective view of one side and end of It the pumping i engines are shown on the platforms on each side, the keel blocks allors, ladders, £20, are shown in the inside Preparatory to receiving a ship in the dock, the water is admitted into the bottom compartment, and the dock sinks to the line indicate by the letters BB, or as low as may be necessary when the ship to be docked Is hauled in placed upon the blocks, and i bored up from the sides The pumps are then set in motion and the dock pumped out till the floor rises above the water-line, when free access may be obtained to all parts of the vessel to be

examined

Bermuda Floating Dock In 1921 the British Government having determined on constructing docks for their ships of war at Bermuda, an engineer was sent to examine the site, but the rock was found to be so porous and fissured that the intention to construct masonry docks was abandoned. Again, in 1851, a second examination was made, with the same unfavourable result, and it was subsequently determined to construct an iron floating dock instead of a permanent masonry dock The harbour is so perfectly landlocked that no danger was to be apprehended of the dock being injured in bad vi other. Accordingly, a dock on what has come to be designated the U principle was constructed, and with s m difficulty towed out to Bermuda,. The accompanying sketches illustrate this dock in various positions The manner of working it is as follows When a ship is to be docked, the water is admitted into the upper chambers, the dock then sinks and assume the position shown at the sketch A ready to receive a ship, which is floated in and grounded on the keel block the water is then discharged from the upper chambers, whereupon the dark ages 10 feet or thereabouts, the pumping Is then commenced till the

vessel is lifted clear of the water

Sketch B represents the dock closed with the caisson and pumped out C shows the dock pumped out and the ship inside dry. D and E show the dock careened for the purpose of being painted or repair ed. This is done by admitting water into the compartments on one side, and pumping it out on the other.

About 8000 tons of iron were consumed in its construction

One of the objections to this description of dock was experienced while lying at Chatham, when during a gale she dragged all her anchors, and it was at one time a question whether she would not be wrecked in the river before she could horse it to

Bermuda.

Speaking of the iron dock at Bermuda, Sir John Packington as president of the Institution of Naval Architects, at one of their meetings, (and " The discussion, to which he had listened with very great interest, impressed him with the belief that the question of floating docks was very much in its infancy, and, while it gave him that impression, it confirme 1 his previous belief that it was a most important miner. It was important from a financial view . . 2 Another important consideration was, whether or not the success of visiting docks would not enable them to accommodate the needs of this country with dock accommodation where there were physical impediments to docks at the present time Bermuda was a most pointed illustration of the He always understood that the nature of the Bermuda rock was such that it was next to impossible to construct a dock there in the usual mode of constructing docks on shore. Bermuda was a most important station for the British Navy, and his belief was, that if they were to have a dock there stall it must be a floating dock, tie was sorry to hear the discouraging language of his hon friend, Captain de Morel), who seems to disparage floating docks altogether, and his authority on all subjects and very high one."

The following is a list of some of the principal floating docks as

yet constructed :

5

oz s a

I

Portsmouth ... United 8Utea.1(51 850 105 4 Penskola .,. " . 1851 350 105-4 Pola in.. Istria. 1857 300 108 Havannah ... Cuba. 1856 300 79 Carthagena.., Spain 1859 324 tons Ferrol ... v 1859 850 Sourabaya in.. Java 1861. 250 Saigon , in Cochin China ...- -Callao ". Peru. 1887 (00

( Stanhouse ... rest ladies ......186« sec 2 ".", .

Bermuda ... 1860 (81 1217 16,700 a at

I , HYDaauiic LIFTS Galvin DOCKS.

I A yen bMutital and ingenious airaogentest for Utting VLMU

requiring repair. Mr US» water, 44 pUftln, ttvMi M draw

for pontoons bytnearaof hydraullcrsms.wssinventedsomrycarB since by Mr Edwin Clark, M Inst. CE. The apparatus re-elected in the repairing basin of the Lord m "V ictorU I) ask a im puny, where it has been worked for some years will consider ii! i

The situation selected for the hydraulic lift was low-lying extent of marsh land between the Victoria Docks and the Thv nos which being below high-water mark was passed early favourite e, as it involved no excavation for the shallow docks into which in pontoons with the vessel on them are floated, the only excavation of importance was for the lift pit and the entrance the dip h of water required in the latter being 7 feet, and in the former only 6 feet, The area of shallow water is 16 acres, which affords sufficient space for floating 15 or 20 pontoons.

The docks g of a vessel by this process consists of two operations; first, tie draw raising of the vessel and pontoon; secondly, the transporting of the vessel to any convenient po turn in one of the eight shallow basins for its repair on the pontoon

The pontoon with the vessel on it, Is and d by means of the leaders in process, of which there are two rows 66 Kct apart Each row consists of 16 cast-iron columns, 4 feet in diameter and its cost apart from centre to centre. 'The length of the dock is about 300 feet, and its width surface ; but as vessels may occur and he pontoon at either end, the e is practically a working length of 35' feet The columns were sunk to a depth of 12 feet into the ground, and the lower parts filled with concrete of The upper portion are occupied by the hydraulic rams. To each rain IS secured a powerful cross head from either side of which d pend

beside tods to which the lower trussed frames or cross girders which conduce' each column with its corresponding one on the opposite side are scoured. The by mulla rams, which are 10 neues diameter and 25 feet stroke, are raised or lowered or maintained at any height with the utmost accuracy by mons of the hydraulic pumps which are worked by a steam-engine on

the operation of lifting a vessel out of water is performed in the following manner A pontoon of sufficient able to support the vessel being placed on the cross girders and the keel and bilge

flocks adjus ed to her form the whole is allowed to sink to the bottom by letting the water escape from under the rams ; the vessel to be docked is then brought over the person and property secured over i be boats, the pumps being set in motion, the pontoon is gradually raised till the vessel rests on the keel blocks, when the bl ge b oils being drawn in and secured, the operation of lifting be continued ml vessel and post you are clear of water, mean Sine the water having been allowed to escape from he Inside of the pontoon, the rams are again lowered and the pontoon and vessel are floated out into one of the shallow latins, and another pontoon being placed between the columns ina lowered, and her vessel may be immediately taken up, and so he operation repeated as often as may be required. I will thus he seen that with one hydraulic apparatus, The number of vessels which may be under going in pairs at any one time is simply de, endent on the number of pontoons available, and the area of shallow basin, or the number of the shallow docks ready to

receive them.

I be hydraulic lift at the Victoria Docks, with its machinery, is said to have cost about £30,00, but the seven iron pontoons and he shallow basins for receiving them, brought the company's

expenditure on the whole establishment up to about £i9>,UuO j

an illustration of it with a vessel raised out of the water on one of the pontoons is gives.

Another hydraulic lift dock, similar to that just described, but larger and more powerful, has recently been constructed at Bom- i bay for the Imperial Government There are eighteen columns in each row, lb feet apart at the centre in the longitudinal direction, Increasing to 24 feet at the ends, and 83 feet apart to his erie ly. Each column is 7 feet 6 inches in diameter at base and 6 tier 6 inches at the upper part. some of the columns are 109 feet in her gin, and they use 86 feet above high-water. The nee and fall of tide at Bombay is about 16 fee and the depth of water where the dock is built variegata 50 to 60 feet The hydraulic presses in each column are 3 feet stroke, and the rams 14 inches in diameter. The transverse girders suspended from the cross

heads, by which the pontoons are filled, are 10 feet 8 inches)

deep.

There is but one pontoon at present attached to this dock, which is fitted in the ordinary manner with keel and bilge blocks

It is 28" feet long by 16 feet broad, 9 feet 6 inches deep ; it weighs 1610 tons, and is capable of supporting a vessel weighing 65 I) tone. The quantity of ii on-work in the lift and pontoon is said to exceed "note ions, and the cost, I have been informed, without the pontoon was about £300,000,

A dock on ina hydraulic lift principle is proposed to be constructed at Barrow in Furness, estimated to oost£lr,3,000, with six pontoons '

Another hydraulic lift dock has recently been constructed at Malta, for the repairs of small vessels: and a contract is stated to have been entered into by Mr. Clark with the Italian Government, for the construction of another at brindisi, to oust £47,00.

1 he dimension s of the three principal docks of the kind as yet

constructed are as follows .

ViotonaDotk. Malta. Bombay.

Length ... 310 feet Sil feet 350 feet ;

Width between rows of

columns .... 62 " 625 ,, 88 " Available draught of water at

ordinary high water 18 " all 30s ,

Number of columns in each

row ... 16 " , 18 " 18 "

Diameter of columns ... 4 " 5 " 6 " { number of presses... T H, H " 72 ,,

Diameter of rain 10 Inches 14 inches 14 Inches stroke of rams ,.. ... 25 feet 30 feet 35 feet Heaviest vessels intended to

be lifted .... 3000 tons 4000 tons 8000 tons I

GRAVING DOCKS OF MASONRY.

Chatham Cock -The accompanying illustrations show the plan, longitudinal and cross sections, of one of the four new graving docks lately constructed at Chatham, on the south side of the repairing basin, from the design of Sir Andrew Clark, It j:. C B Their dimensions are as follows Long h on the floor, 416 feet 6 inches, 456 feet at the coping, 108 feet in width at the coping, bu feet wide at the entrance, and have 31 feet 6 inches of water to the sill at high water spring tides, and 28 feet 6 inches at high water neap tides. These docks will thus be capable of taking in helarge<tof the iron-clad ships of the navy The masonry of he foundation and side walls was laid on a bed of gravel found underlying the Medway clay,

in the construction of these works convict labour has been very < extensively used the number of convicts employed ranging from 360 to ditto and upwards and it has been remarked that so far from the work performed by the convicts being of an inferior character, it bears favourable comparison with that executed under contract by free labour.

Portsmouth Docks The accompanying Illustrations, showing he plan, longitudinal and cross sections of the Portsmouth docks

will give some idea of the mode of constructing graving docks in I soils of the kind met with in this instance, and which consisted of mud for about 30 feet in depth, with a substratum of sound yellow clay Underlying it,' the clay furnishing the male ml for the bricks so largely used in the construction of the works, and which were made ent e y by convict labour

At the commencement of the works about 4-0 convicts were constantly employed, but more recently the number has been increased to over too At first they were only employed on the under kinds of work, but latterly they have been, as in the case of Chatham, not only employed In brick-making, pile-driving, Sea , but also in constructing the roads and railways in the dockyard, as well as building portions of the masonry of the brain walls, but they have been used with greatest p oh. so making the bricks, for which the clay found in the excavation is admirably suited The

new Portsmouth docks are of the following dimensions rt-pectiTtly The double deck 636 feet long, 83 feet wide, with 27 feet of water on the sill the two lock docks are 418 feet long, 83 feet wide, with 32 feet at high-water on the sill. The deep ducks are to be four in number, 20 feet on the floor, 110 feet between copings, 63 feet in width of entrance, and 81 feet of water on the

ill.

Brest Dock. The new double dock at Brest, having a division in the centre to admit of either one very large or two or more smaller vessels being docked at one time, is THE feet long, 97 feet wide, and has 55 feet at high-water spring tides on the sill

The new Somerset Dock at Malta is 428 feet long on the floor, 468 feet over all, 104 feet wide, at coping, 83 feet width of entrance and the depth of water on the sill is 33 feet 6 inches. The total cost of the dock and entrance was £150,000, and the cost of temporary pumping, for machinery, coats, off, to , came to over iSo.iOO. . '

1 he Alfred Dock at Melbourne, constructed from the designs and under the superintendence of W W. Wardell, Esq., M. mat C.E , Inspector General of Public Wo: ks, is 436 feet on the floor, 65 feet over all, 07 feet wide between the comings, and 60 feet in entrance, with 24 feet 6 inches at low water and 26 feet 6 inches-

on the sill at high tide. It is stated to have cost £123,uOO Pur he dock proper, and (20,000 for pumping machinery and caisson 'This dock is undoubtedly one of the finest out of England, it out in the world; and for convenience in its general arrangements and excellence of workmanship, in every detail, it stands second

to none.

Having; In the foregoing pages given a brief description of some of the principal kinds of docks which have been constructed showing what modifications in the original type of masonry dockshave been adopted by engineers to meet the peculiar circumstances of each case with which they were called upon to deal. I shall now endeavour to show as concisely as possible the kind of work which, in my opinion is best suited to the peculiar circumstances of this port. But I would first invite attention to the two graving docks already constructed here

The W atcrvitw Dock, constructed by Mr. Mort, Is of the very plainest kind of work, nothing more In fact having been required than a simple excavation in the solid sandstone rock, resembling somewhat in form the ships it is intended to receive. The natura lock forms the sides and floor of the dock, which, while sutilLiently Left to be easily worked, is yet thoroughly sound and watertight, so that no expensive masonry lining (absolutely necessary when the soil is charged with water, and which involves the greater part of the expenses as well as the chief difficulty in the execution of such works is required, almost the only masonry in the Waterview Dock being the pier-head at the entrance for the support of the caisson.

It will be observed that no work could be more simple or easy of construction, and no book could be more convenient or a lie I am enabled to speak from personal experience in this matter as to the former, having acted for Mr. Mort as consulting engineer

during its construction.

The Fitzroy Dock has also been scooped out of the solid rock in a manner very similar to the Waterview Dock ; but in consequence of the occurrence of a bed of shale at the bottom, u was found necessary to cover the floor with an invert of solid masonry

On some portions of the sides masonry for the altars was keen required where the rock was unsound, or where the shale binds showed themselves. The pier heads at the entrance and the sill, where the caisson rest, are all of heavy masonry.

Ko kind of ground could be more suitable for dock construction than the sandstone of this harbour, which, while so soft as to be worked with ease, 18 strong enough to stand without masonry lining, and is all but perfectly watertight.

to attempt, therefore, to introduce here any of those complex arrangements or forms of dock which have been forced on engineers at other places by the peculiar difficulties they had to contend with would be as manifestly unwise as unnecessary.

In devising the most suitable form of dock for any locality, the engineer first considers the character of the ground, or the material he has to work in. It is bo tock-ltssu ed or permeated by water to a great degree, or if it consist of gravel, quicksands, or soft boggy soil, in which there would be difficulty in obtaining a foundation, such as is commonly to be met with on the banks of rivers or shores of harbours, be will find himself compelled perhaps to adopt some form of floating, balance, or sectional dock or hydraulic lift such as I have described. But if, on the other hand, the ground be central for the commotion of permanent docks, the many advantages which they possessed in the economy, facility, and safety with which ships can be docked and repaired in them, will always give them a preference. It was probably the many difficulties encountered in cows quoting the New 'York Dry Dock, arising from the enormous quantity of water met with, which retarded its completion for about ten years and brought its Cost up to half a million sterling, coupled with the abundance and cheapness of timber in the United States, which induced the Government engineers of that country to turn their attention to the construction of the timber sectional and floating docks which they have adopted, but which however designed, must always be worked at great disadvantage and be costly to maintain, from the perishable nature of the material of which they are constructed. It was similar difficulties, in the cases of Carthagena, Ferrol, St Thomas, Bermuda, and Callao, which led to the adoption of Iron floating docks at these places, to which similar objections as to their non-permanence apply, though not perhaps in as great a degree. The iron plates, however carefully painted, must corrode, and the rate of corrosion in the warm sea water of these low latitudes is rapid enough to be an objection to its application in this way.

The corrosive action of sea water on cast-iron is not nearly so rapid as It is on wrought-iron 3 except therefore, in so for or as applied to the pontoons, the foregoing observations would not apply with much force to the cylinders and other apparatus of a hydraulic lift ; but there would brother objections to the adop-tion in this sort of this latter form of dock of even greater moment, such as the difficulty of safely securing a large ship on a pontoon in any part of the harbour, exposed as it is to the force of the southerly and easterly gales, of which we have all had experience. v l .

In order to work a hydraulic lift with safety, It would be necessary to form ? dock or docks for the pontoons, which would

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dock alone for a larger ship. There is no suitable place in the i eli bbuutbuod of the Dockyard Establishment of Cockatoo where a hydraulic lift could be easily placed, and where the pontoons could be taf. ly moored. 8' me sheltered spots might no doubt be land at the heads of some of the caves of bays within the harbour; but this would entail either the removal of the dockyard citibiithmtnt, tools, &c, end abandoning the present dock -.»bichioeije, I apprehend, world r< commander thence* circles and expense of working two distinct and separate tests.

blubnieniB

On first considering the subject of a first-class dock at Cookator, 1 was disposed to think that it would be better to enlarge Represent ? eek than construct a new one altogether; but after invite e y considering the subject in all its bears go, I have been con pi land to change my opinion, and I am now entitled, for the following, amongst other reasons, that it will be better to construct a new dock at the western end of the island, with its head to fill g eastward toward is the present duck.

In the first place the FitzRoy Dock as it is at present, is of a most convenient size for general purposes, and we eat to be margin it would necessitate closing it for a considerable time since the alteration was being made; for although it might ' | ci bags be used occasionally using the interval, it would, if the

. n statement were carried out by contract be considered better to close it altogether during the progress of the work.

Kcciidlj, to deepen the nil to as feet and widen the entrance to Mr le« t which are the minimum dimensions for a first-class dock, it was d be necessary to endure the pier heads with a coffer-dam which would be a work of some considerable difficulty and xiii', owing to the sand having been removed and the look laid bare for blasting out 'be present entrance.

In the third place, the deepening of the channel outside the dock would involve much under water rock excavation as well as a large amount of i ridging.

And lastly and, in my opinion, the most formidable objection li- that I lie course of the currents, both of flow and ebb, set across the line of the axis of the present dock nearly at right angles. The inconvenience, and indeed danger to very heavy ships from a big crush was made plain when the French iron-clad At., ne he was bell, g docked. Being a strong flood (ships should dusk s be docked at ft cut half 15th a-quarter flood), the current caught the vessel on the starboard quarter and showed her out of the line of The a rock, and it was with the utmost difficulty that even with her powerful crew, she could be got and kept in the lil opt r life for taking the keel blocks. The line of the axis of the duck is shoal a considerable angle with the north-easterly as well so southerly winds which at times blow with considerable force, and doing g the prevalence of which great difficulty is ex-peril need in docking the gc vessels.

li the present dock were charged now caisson would be required, for I find, OF carefully going into the manor, that the cost of cutting g, lengthening. raising, and strengthening the present caisson to make it suit the wide- and deeper entrance would make it ainiOB'., is not quite, as costly as a new one.

As regards the site of the proposed new dock at the western side of the island, it is completely landlocked, being sheltered on the south by a kennel Point and Schnapper Island on the west, north-west, and north by Spectacle Island, Pulpit Point, and Hunter's Hill; and on the north-east and east by Cookutoo

j IslAnd Itself, The head of the cook pours east north-east,

so that the prevailing summer winds, which blow i 1 iron north-east, would tend to keep a ship entering the. , dock in the proper line for the blocks, and the flood-tide on the

south side or the island, passing up almost in a line with the

1 dock's axis, would also tend to maintain a ship in the proper Fune for being docked. The direction of the flood and ebb our-'

rents will he seen on reference to the current chart which accom-, parties this paper. Some of the ebb currents will be observed to. run across the axis of the dock, but this is unimportant, as vessels

are not, except in cases of extreme emergency, docked on an, ebbing tide, .

There is ample depth of water off this part of the island for ships of the heaviest draft, with good anchorage. The deep Waters comes close in BIIOIC near the proposed entrance to the dock, and! there being a sufficient depth of Band and mud overlying the rock e, at this point, there would be little difficulty in constructing a' corrosion for building the pier heads and breaking out the entrance the rock upon which the dock would be carved in' tout d. and may be said to be almost free from water to a depth, of 43 feet, or about 10 feet below the floor of the dock. This is seen in) the trial shafts which I have had put du was along the centre line of the proposed dock. The leakage, which is mainly fresh water off the island, is insignificant.

in determining the dimensions of the new dock, I have been offices by those of the new first-class docks at Chatham, Portsmouth, and Malta, and the Alfred dock, Melbourne ; but as any increased dimensions in our proposed cock would be simply a matter of a little more or less . excavation, involving little or no indecency,! have thought it should slightly exceed the dimensions of those other docks described, so that we may justly boast of Having in Port Jackson the largest single dock in existence.

The list given in an appendix, of the dimensions of some of the principal dry docks, is taken from Span"s "Dictionary of Engineering."

E. O. MORIARTY, ; Engineer-in-Chief for Harbours and Rivers. a