English: At the Gloucester Waterways Museum at the Gloucester Docks.

Boats: A narrowboat and S.N.D. No. 4.

Museum Dredger and Sabrina 5

Steam Dredger SND No 4

    SND No 4 steam dredger was built in 1925 for the Sharpness New Dock company by the De Klop shipyard at Sliedrecht in Holland. (Another page features the earlier dredgers used on the canal.) Supplied with SND No 4 were two pairs of clogs - one pair for the engine driver and the other for the fireman, who would both be standing on oily plates in the engine room. The boiler was originally coal fired but is now fuelled by oil. It provides the power to drive the chain of buckets, each of which can lift 7 cwt (356 kg) of silt. When the bucket ladder was lowered to the required depth, the buckets scooped up the mud on the canal bed and as the buckets turned over at the top of their travel, the contents ran down a chute into a barge moored alongside. As dredging progressed, SND No 4 was moved sideways and forward by two steam winches on the deck which could wind in or let out wire ropes, the ends of which were attached to the canal banks. To move over long distances between dredging operations, the dredger was towed by a tug.

    SND No 4 was mainly used to dredge Gloucester Docks and the Sharpness canal to a depth of 16ft and to dredge the dock at Sharpness to 24ft. At times SND No 4 also worked in the entrance and tidal basin at Sharpness. These operations typically removed 35,000 to 40,000 tons of mud from the canal and docks each year until 1981, when SND No 4 was replaced by a diesel-electric powered dredger.

In 1988, SND No 4 became a working exhibit at the Museum, and visitors were able to watch demonstrations of the steam engine turning the buckets. Unfortunately, this role was interrupted in 1990 when a culvert failure down the canal caused a dramatic drop in dock water level and SND No 4 rolled over and sank. The dredger was raised by British Waterways staff, and then a long programme of clean-up and refurbishment was carried out by volunteer Friends of the Museum and Museum staff. SND No 4 is once again a working exhibit, operated and maintained by the Friends.