The Bertha was built, of riveted iron, in Bristol by George Lunnel, & Co. copying a design, by John McLean to deal with silt in the Floating Harbour. This was the BD6 built in 1843. It is a Bed leveller or plough dredger, with a large metal blade, was at the bottom of a 24 ft (7.3.m) long timber boom, or spud, which could be dropped or lifted similar to a bulldozer on land.
Bertha is a steam-powered boat built in 1844 to remove silt from Bridgwater dock in Somerset. It is the oldest operational steam vessel in Britain, and possibly in the world. It is part of the National Historic Fleet.
Bertha is 50 feet long and 15.5 feet wide, with a tonnage of 60 ton. The power is from a coal fired single cylinder steam engine providing steam at 40 pounds per square inch A large flywheel and drive shaft drove a single-reduction spur wheel drive.
The vessel was anchored by chains to bollards on opposite sides of the dock, and the engine pulled it, with the scraper blade, to the centre line of the dock. The blade was raised and Bertha was hauled back to the dock wall, where the chains were unshipped and fixed to the adjacent bollards, and the operation repeated. When one side of the dock had been done, Bertha was unfixed, and turned round so the operation might be repeated on the other half of the dock.
The resulting long mound of mud was flushed out of the dock into the river on a falling tide, after opening the sluices.
She was surveyed and photographed in 1962 by the technical historian, George Watkins (see below), on the same day he did the Telescopic Bridge .
Bertha worked in Bridgwater Docks, after the connection of the Bridgwater and Taunton Canal to the River Parrett, from 1844 until 1969. The vessel was initially owned by the Great Western Railway and then British Railways. She was then taken to the Exeter Maritime Museum, where she was shown working with the help of John Selby (welder and fabricator in Spaxton, Somerset). In 1997 it moved to the World of Boats at Eyemouth where it was restored. The Eyemouth Maritime Museum closed in 2016 and Bertha is now in Bristol, on the SS Great Britain site, but is not on public display.