100 YEARS OF THE UK’s MARINE AGGREGATE DREDGING INDUSTRY
The UK has the second largest marine aggregate dredging industry in the world, Japan having the largest.
1912 saw the RMS Titanic sail on her maiden fateful voyage, Robert Scott reach the South Pole, Barnsley beat West Bromwich Albion to win the FA Cup and Great Britain come a creditable third, after Sweden and the USA, in the Stockholm Olympic Games. Also, on 15th June that year, the 49ton grandly named, steam driven suction dredgerCity of York sailed from Bristol and dredged a cargo of sand in the Bristol Channel thus marking the start of the modern British aggregate dredging industry.
City of York
Dredging stone from the seabed had taken place for at least two hundred years prior to the City of York’s maiden voyage with ballast for ships probably being the earliest reason for doing so.
In the early days, both aggregate and maintenance dredging was the by way of “spoon and bag” which both Holland & Italy claim to have originated but is thought more likely to have been introduced in western Europe and Britain by the Phoenicians or Romans who, as their empire expanded, brought the practice of dredging with them. The 1829 edition of the London Encyclopaedia gives an exhaustive description of spoon and bag dredging or “ballast heaving” which allowed two to four men to lift up to sixty tons of ballast in a tide from a depth of some three fathoms:
The common dredging boat or barge is worked by two or more men, by whom the gravel, or ballast, is taken up in a leather bag, the mouth of which is extended by an iron hoop , attached to a pole, of sufficient length to reach the bottom: in the small way, two men are employed to work each pole. The barge being moored, one man takes his station at the stern with the pole and bag in his hand, the other stands at the head, having hold of a rope, tied fast to the hoop of the leather bag. The man in the stern now puts the pole and bag down, over the barge’s side, to the bottom, in an inclined position. The hoop being farthest from the man in the head of the barge, and having a rope , one end of which is fast to the gunwale of the barge, he passes it twice round the pole, then holds tight: the man in bow now pulls the rope, fastened to the hoop, and draws the hoop and bag along the ground, the other allowing the pole to slip through the rope as it approaches the vertical position, at the same time causing such a friction, that the hoop digs into the ground, the leather bag receiving whatever passes through the hoop: both men now assist in getting the bag into the barge, and delivering its contents. When the bag is large, several men are employed: and, to increase the effect, a windlass, with a wheel-work, is sometimes used. A chain or rope is brought to the winch from the spoon, through a block suspended from a small crane for bearing the spoon and its contents to the side of the boat, and bringing it over the gunwale to be emptied into it. The purchase rope is led upon deck by a snatch block in the proper direction for the barrel of the winch. From two to four men can, with this simple apparatus, lift from twenty to sixty tons a tide from a depth of tow and a half to three fathoms, when the ground is favourable.
The Encyclopaedia also mentions that “…in this manner the convicts at Woolwich upon the Thames, have been long employed to perform the ballast-heaving or dredging…” and that “…the bucket dredging-machine, whether worked by men, horses or the steam-engine, is a great improvement of the above.” Doubtless all dredger men would agree with that.
For hundreds of years copperas stones, some as large as a man’s head, were gathered on several east Kent and Sussex beaches with an account in the early 17th century recording that it was not uncommon, in the space of a single tide, for the local paupers to each collect between ten and twenty bushels of copperas stone and their children four bushels. The stones were gathered into heaps on the beach and then loaded into flat bottomed barges or hoys which were used to transport them to one of the nearby Copperas Houses. In the Copperas Houses the stones underwent a lengthy water based leaching process which produced green vitriol / copperas / hydrated iron sulphate. Copperas was the principle raw material used in the production of many early black dyes and inks and was also used in the manufacture of brimstone (sulphur) and oil of vitriol (sulphuric acid).
As copperas stones were encapsulated in the London clays found on the Kent & Sussex shores, particularly after storms when they were washed up in considerable quantities, it was perhaps inevitable that a trade dredging the stones offshore would develop…and it did.