12 February 2007 by stepheng
They may not be the most glamorous of ships but I, Stephen Guy, have a soft spot for the dredgers which play a vital role in keeping ports open.
In the Port of Liverpool an incredible three million tons of silt is removed by dredgers every year from shipping channels and docks. The silt is taken to specially-designated spoil grounds out to sea well clear of the Mersey Bar.
Dredging the Mersey started in 1890 to counteract the increasing problem of silt deposits in the port, especially in the vicinity of Askew Spit at the entrance to the Mersey estuary. Two hoppers equipped with sand pumps set to work at the Bar. During the first 10 months of dredging, 350,000 tons of silt was shifted.
The Mersey Docks and Harbour Board then decided to build larger dredgers including the 300-ton Brancker which started work in 1895.
Improvements to the port channel through dredging – together with better facilities at the Prince’s Landing Stage and neighbouring Riverside Station – placed Liverpool in a good position to maintain her hold on the north Atlantic liner trade. Liners and other ships continued to grow in size.
At Merseyside Maritime Museum there are several models and photographs linked to dredging. Am impressive10 ft long model of the Leviathan (shown) gives some idea of the huge capacities of dredgers. Built by Cammell Laird’s, she was a familiar sight on the Mersey between 1909 and 1963 when she was scrapped. The 465 ft long Leviathan was fitted with a triple-expansion steam engine and could carry 10,000 tons of sand. The machinery used in removing silt is shown in great detail including four huge sand pumps that were lowered to the riverbed.
Not all dredgers work in the approach channels. Another method of removing silt was employed by the Mersey No 26 of 1948, a grab hopper dredger. A model at the Merseyside Maritime Museum shows her with three cranes which scooped up the silt. Mersey No 26 was designed to work within the confines of the dock system where silt, brought in each time the dock gates open, has to be cleared regularly. She used crane grabs rather than buckets or suction pumps, and took 1,350 tons of silt to the spoil grounds before opening the doors of her bottom to dump the load.
A new Maritime Tale appears every Saturday in the Liverpool Echo.
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