1056

THEORY AND PRACTICE OF ENGINEERING.

Book II.

The method adopted by Goubert to raise a sunken vessel which had lain 42 yearsin the roads of Renondelle was somewhat similar; its depth was 17 feet at low water ; thebar made use of was the mast of a ship 83 or 34 feet in length, armed with four Hat ironbars, and pointed at the end with an iron rod 23 feet long; the two ropes which were to bepassed under the hull were attached to this point, and, previous to this being attempted,Goubert dug small channels in the mud, one of which he made perpendicular to thekeel, and another he formed on the opposite side in an oblique direction : after intro-ducing the mast into the first-mentioned hole, and placing it by means of tackle in anoblique direction, with a pile-driving engine he forced it through the mud into the channelcut to receive it on the opposite side, and then fastened a rope to the iron point; thewooden mast was then separated from it, and, by means of three capstans, the ropeswere pulled through, and when all were passed under the vessel, they were made fast to tworafts prepared to receive them, and, by means of the tide, the whole was worked into shallowwater, where it was demolished.

Another method adopted when the position of the vessel which has been sunk is thoroughlyascertained, is to employ two vessels to pass a chain cable under or around her : theseare placed near the bow, with the cable suspended from one to the other in such a mannerthat it sweeps along the ground ; the chain is then moved backwards and forwards untilit comes under the sunken ship; the two vessels are then moved astern, and the ends of thechains are brought together, and passed through an elliptical ring sunk close to the stern, theends of the chain being made fast : when this main chain is in its required position,others, called bridle chains, are fastened to it at various convenient distances, and also toother vessels at the time of low water; then, as the tide Hows, the vessel sunk is elevated,

and afterwards floated to the shore.

Hedgehog, in use for removing mud in rivers, or the accumulation on the land sideof sea-sluices : it is cylindrical in its form, like a garden roller; around the outside areattached eight or more longitudinal ribs, each of which isarmed with as many spades or hoes fixed in them firmly bybolts and screws. This cylinder revolves on pivots in gudgeonsin the side frame, which is made of oak, and diagonallybraced in front of the roller or the revolving cylinder. Theiron spades are in width 4 inches, and in length 7, and areplaced about 7 inches apart: at each end of the shaft isattached a strong chain, by which its motion is insured, andwhen used it is attached to the stern of a barge, which inLincolnshire is usually drawn by horses ; sometimes a bargeis moored at some distance from the mouth of the sluice to becleansed, and the hedgehog is moved backwards and forwardsby blocks and chains : such a machine made of oak, and wellbolted together, is most effective; as the cylinder revolves onits axis, its sixty-four spades are all brought into work, andin their progress disturb a vast quantity of mud, which thestream through the sluice aids in carrying away. The timberframe has its scantling 6 inches by 4, its cross-stays from oneside to the other being placed about 3 feet apart; and betweenthem are introduced diagonal braces, which are made fast tothe frame and stays by iron bolts. The stocks on the cylin-drical drum or iron wheel are in length 6 feet, and made of oak6 by 4 inches, into which pass the iron spades.

Floating Clough , for scouring out the channel of a river atGreat Grimsby , as well as other channels of the Humber.

A frame 12 feet in length, 9 feet in width, and 6 feet deep,of timber 6 by 4 inches, covered with 2-inch plank ; throughthe middle is a culvert 2 feet 6 inches in width, made withplanks, with a small lifting door at one end. At the bottomis secured two beams, which project in front, and which serveas feelers to keep the machine in its right position : in thefront are placed frames of timber shod with iron, cut in a ser-rated form, which, by means of a lever, can be raised at plea-sure at the sides of the machine are wings, sloped to accom-modate themselves to the fall of the banks, and when the wateris at high tide it is moored into the middle of the stream, with the wings extended bymeans of ropes, and at half ebb the water is admitted by plugs, and the machine sinks tothe bottom; the plugs are then replaced, and it remains in this position till full ebb; theiron shod frames, with teeth like a saw, are let down in front, and the whole machinebeing forced along by the tide, scrapes up the bottom, and the mud disturbed is carriedalong with the return tide for a distance of three miles or more in the space of two hours.

Fig. 1021