ria 



DREDGING. 





Bug and 



*poon 



drcdge. 



Spoon. 



their harbours ami navigable canals. These early ma- 

 chines were not contrived lor lifting stuff, but only to 

 loosen it. that thr sluices which were OOMtraetecl for 

 the purpose ot' scouring might l>c more effectual. The 

 machine i nn-i-tcd of large Kir-; or prongs, like :\ number 

 of forks, placed vertically in a frame, and being fasten- 

 ed to a barge placed in the line of the sluice-., the whole 

 was impelled forward by means of the current, and 

 caused a more powerful scour. 



The first kind of dredging machines employed to any 

 extent in Britain, consisted of a large plate of iron, 

 about four feet long and eighteen inches deep, and 

 sharpened on the uiulcr edge. To each end of this plate 

 of iron, a plank of hard wood wan fixed to tenons cut 

 in the iron, the shaqH-ned edge of iron projecting about 

 Four inches below the wooden sides, which should be 

 about five long, tapering to ten indies deep at the point, 

 where a bar of iron is fastened to keep the two ends asun- 

 der. The whole formed something like a box without 

 bottom or top, eighteen inches deep at the one end, and 

 ten inches at the other. From the two extreme points 

 of the wood a chain is fixed for attaching the principal 

 working rope or chain. 



In order to put the machine in motion, it is requisite 

 to have a punt moored on each bank of the river direct- 

 ly opposite, and on each of these punts a capstan or 

 windlass, the one for drawing across the empty dredge, 

 and the other for bringing it back. In the course of its 

 passage, the dredge is generally filled, and by means of 

 the capstan it is drawn so high up that men at low water 

 can remove the stall' with shovels. Where the .shiftings 

 are not frequent, a capstan or windlass may be pla- 

 ced on the bank of a river, and the operation jK-rfonned 

 as before. But as the method by the machine just 

 deserilxjd, is very tedious where dredging ofgre.it ex- 

 tent is required, it is now little used except in levelling 

 foundations under water, for which it is well adapted, if 

 the material is soft sand or mud ; but where there is 

 ttor.y gravel, it is necessary, in place of having the 

 mouth of the dredge straight, to have it made with 

 bars of iron curving towards the under edge, and 

 placed about four inches apart, when stones of consider- 

 able size may be brought to the side, and removed in 

 the manner we have already noticed. Machines con- 

 structed agreeably to the foregoing principle, have for 

 many years been employed in deepening the- navigable 

 part of the river Clyde between Glasgow and Dumbar- 

 ton. 



^ e come now to the operation of dredging, which is 

 performed by the bag and spoon. This kind of dredg- 

 mg has been carried on to a considerable extent under 

 the direction of the Trinity-house at London for deepen- 

 ing the river Thames, and also for obtaining ballast to 

 the vast number of .ships which frequent that noble 

 river. The convicts at Woolwich have been long em- 

 ployed in the same manner for deepening the river, and 

 obtaining stuff for embankments and other government 

 works at Woolwich. 



The spoon consists of a ring of malleable iron, two 

 feet wide, and two feet four inches deep ; sharpened and 

 steeled on the under side four ii.ches broad for alxmt 

 one- third of its circumference. and pierced on the inner 

 edge with holes for the lacings of the b;ig. The re- 

 mainder of the ring is of MOM iron one inch and a half 

 diameter, and on the upper side, or that opposite to 

 the mouth, a hose must be welded to receive the j>le 

 or handle, which, to a spoon of the above size, should 

 !> from four to five inches diameter: the length of this 

 ' handle w ill always be regulated by the depth of 



water. From each side, about halt' way up the jpoon, T>- 

 a chain two feet and a half long is fastened, and these ~ . ' 

 chains come together by a small ring in the middle, to 

 tin- place where t' e working rope i- made 1 



The bag is gcnerallv made of strong tanned leather, 

 of the si/.e of the spoon at the mouth, narrowing con- 

 siderably towards the bottom, that it may be the easier 

 discharged. It is about three feet and a half deep, 

 and is laced to the spoon with leather thongs, and per- 

 forated to allow the water to escape. 



In order to work this spoon in navigable rivers, har- i 

 hours, &e. it is nccc-ary to have a Hat built barge or 

 lighter, from ;;() to 50 tons burden, mounted with a 

 small projecting crane work, made to throw out of 

 gear ; and to within nine feet of this projecting crane, 

 a rail should be placed to assist the spoon holder, and 

 prevent him from falling over the barge. On the end of 

 the barge where no crane is placed, a snatch block 

 should be fixed, through which, and attached to the 

 bottom of the bag, a small rope should be reeved. 



The barge being thus mounted, and moored o\er the OpentkiB. 

 place where it is proposed to dredge, and one end of 

 the working rope being fastened to the chain of the 

 spoon, and the other end to the barrel of the crane, the 

 man who is stationed at the handle or pole of the spoon 

 immediately tumbles the spoon into the water. At the 

 same moment the man at the crane work throws it out 

 of gear, when the third man seizes the small rope, which 

 is reeved through the ynatchblock, and fast to the bottom 

 of the bag, with which lie runs along the gunwale, and 

 prevents the SJMJOII and bag from sinking until it get* 

 near the other end of the barge, when the man at the 

 jK)le turns it up, inclining the pole head towards the 

 crane end of the barge, takes a turn with a small rope 

 round the pole and rail, which keeps the spoon dredg- 

 ing along in its proper position, while the man at the 

 crane, assisted by the other (who was employed at the 

 snatchblock being now disengaged), draws along the 

 spoon until it be nearly under the crane, when the man 

 at the pole inclines it backwards, and the contents (now 

 deposited in the bag) are hoisted up, and by their joint 

 assistance emptied into the barge. A small tackle of 

 pullies may be suspended from a beam to empty the 

 stuff into the barge. When the bag is discharged, they 

 proceed as before, until the barge is loaded. 



The bag and spoon dredge may also be successfully 

 employed in dredging the foundation of bridges, &c. 

 by erecting a platform to answer the purpose of a barge. 

 The platform may be projected as the work advances, 

 and the stilt!' taken up removed from the platform by a 

 gangway and wheel borrows, where it cannot be other- 

 wise disposed of. 



In a commercial country like Britain, where ships 

 have been gradually increasing in si/e, and more es- 

 pecially where harbours Ivive little rise of tide, it is a 

 matter of the greatest importance to construct dredging 

 machines, which will increase the depth under low- 

 water of spring tides, in a more speedy and effectual 

 manner than any we have yet described ; and it is a 

 fact well known, that all rivers, harbours, and canals, 

 have a tendency, less or more, to fill up. Drei! 

 machines should l>c like the tools of a j>erfect workman, 

 never out of order. 



Improved dredging machines on the principle of *I) I: 

 endless chain, ha'\e been undergoing such improve 

 ments as experience has pointed out; and it may not 

 be deviating from our ge: eral plan, to rrn'nrk. th.it 

 when these machine* were frst constructed, horse, were 

 employed as the moving power, and had a circle ;;>- 



