49 ft 3 in
Bertha has a tonnage of 60 and is constructed of riveted iron with a timber superstructure.
The steam engine is a single cylinder double action engine and operates at a pressure of 40 pounds per square inch, steam is raised in a coal fired boiler of unknown vintage, the motion is transferred to the main drive shaft which can be recognised by the large flywheel by means of a single reduction spur wheel drive.
Sometimes mistakenly referred to as a dredger, Bertha is in fact a drag boat. Where as a dredger operates by lifting the mud and silt out of the water, a drag boat is rather like a floating bulldozer with a submerged blade which scrapes the material along the bottom.
Although steam powered Bertha has neither screw propeller nor paddle wheels but is moved by hauling herself along a chain, the ends of which are secured to quayside bollards.
Bertha is believed to have been designed by the eminent Victorian engineer Isambard Kingdom Brunel and has the distinction of being the oldest operational steam driven vessel in Britain - possibly the world.
Bertha was probably designed in Bristol and assembled in Bridgwater where her role was to keep the docks clear of mud and silt. To do this, the blade, mounted on a sliding pole, was lowered by means of a chain. The vessel then hauled herself along the main chain bringing with it the mud and silt which was dragged out into the river Parrett where it was carried away by the tide. The vessel then hauled herself back along a lighter chain and the procedure repeated.