In 1798, the Inspector General replaced some of the horse-driven pumps employed to raise and lower water levels in the docks and basin at Portsmouth with pumps driven by steam power, housed in an engine house on top of the reservoir. Their effectiveness was demonstrated on numerous occasions in 1799. From the beginning, the boiler of the steam engine needed a supply of fresh water and a well was dug to supply cisterns from which a supply of water was piped throughout the yard. The pumps ensured water could be thrown over any fire from hydrants located around the yard. In 1801, Bentham recommended a moveable steam engine to pump and drive throughout the yard. At the same time, a steam-powered dredger was built and had it first trial in March 1802. It was the first bucket-ladder steam dredger and in November 1802 it was raising 10 tons of silt from the Portsmouth harbour in half an hour. A second similar dredger was built in 1806 for the River Thames. Meanwhile, in 1800 a Boulton and Watt engine was purchased to alternate work with the first smaller Sadler engine which in 1805 was replaced by a second Boulton and Watt engine. These new engines provided a steady rotatory motion suitable for driving wood-working machinery and permitted the establishment of what became known as the Wood Mill. The Mechanist, Simon Goodrich, managed these new installations, but they also gave rise to a new group of yard artificers, the millwrights.