Chap. VIII.
347
half that slope on the inside. It is raised 5 or 6 feet above the level of high water atordinary spring tides, and the top is covered with large blocks of roughly hammeredstone. The breakwater is protected by a shoeing of rubble stone; by narrowing theentrance, it materially deepens the channel; a permanent depth of 5 or 6 feet water hasbeen obtained.
By means of a dredging machine, worked by a steam-engine, the interior of the harbourwas deepened ; an additional 3 or 4 feet of water has been obtained, throughout the wholeextent, for more than a mile in length, so that vessels of any description arrive at the quays,and there is no necessity for lighters.
In the year 1815, 900 feet in length of the new wharfs and the capstan towers werebuilt, as well as the embankment formed, on the south side of the wet dock ; the worksremained in this state till 1830, when 1350 feet of new wharf was built, and the embank-ment of the wet dock was proceeded with, as well as other portions of the work.
The whole breadth of the new wharf is 100 feet, and its foundations are laid on a plat-form of timber, resting on piles, with a row of sheet piling in front; the outside face of theother wharfs is built with granite ashlar, backed with hammer-dressed masonry, laid inlime mortar, and the outside joints pointed with Parker’s cement.
The general bottom of the harbour is sand and gravel, so that it was necessary to havecoffer-dams, for the purpose of constructing the foundations for the various buildingserected, and chain pumps were used.
The right bank of the new channel was completed in 1832, its length being 1630 feet,
and that of the spill or water bank, 4107 feet.
The cost of these works was as follows: —
£
Extending the piers and breakwater - - - 81,955
Dredging the inner harbour - 17,999
Constructing new wharfs and common sewer - 39,738
Forming a new channel for the river, including the capstan, towers, and jetty,
also constructing bulwark and embankment - 15,398
Making a communication bridge to the Inches ... 5,500
£160,590
Since these works were performed, a new channel for the Doe has been opened, and aspill water channel formed, by which means the river is kept entirely out of the harbour.A cast-iron turn bridge has been constructed across that part of the harbour called theInches, which, by means of an embankment, has been considerably enlarged. A wallhas been built, 3200 feet in length, forming a spacious quay, 100 feet in breadth, andpaved throughout; this is in addition to the 920 feet length previously built. A quaywall 1200 feet in length has been also built on the Inches.
There is now altogether 6290 feet of quay berthage to this harbour, and a building slip,of a size sufficient to receive the largest steamers, has been built according to a patentobtained by Mr. Morton.
Mr. Morton’s mechanical slip was patented in the year 1818, and it has been put downat most of the ship-building ports in the kingdom; the patentee, in giving his evidencebefore a Select Committee appointed to inquire into its merits, enumerates about fortyslips built a few years after its invention.
The chief feature is that of placing a complete wheel carriage underneath the bottomof the vessel, which carriage has a long straight beam extending beneath the wholelength of the keel, with blocks fitted, upon it for the vessel’s keel to rest upon. Asall vessels are straight at the underside of the keel, or have some determined curvature,it is easy to dress the blocks, which are placed on the middle beam of the carriage, toeither a straight or curved line, before the ship is taken up ; and the slip is so constructed,that the form of the carriage undergoes no alteration when the weight of the ship Isplaced upon it; and the carriage is substantially borne by three parallel lines of ironrailway, founded upon either timber and piles or masonry, upon which it traverses uponnumerous wheels or trucks of cast-iron.
The ship, when placed upon the carriage, is kept in its perpendicular position by crossbearers, on which is adapted other timbers fitted to the curvature of its sides, forming acradle; it is then, by means of tackle, drawn up an inclined plane, by men working at acapstan, or at winches with cog-wheels, the chain being attached to the carriage, andexerting no strain on the ship.
Between the railways is laid a cast-iron rack having serrated teeth, into which strongpalls catch, and which prevent the carriage from running down the inclined plane, in casethe tackle gives way.
Previously to this system being adopted, it usually cost 170/. to haul up a ship of