They supplied Fulton in 1807 with his first engine, by means of which the Clermont made her first voyage along the Hudson river.

They also supplied Fulton and Livingston with the next two engines for the Car of Neptune and the Paragon.

From that time forward, Boulton and Watt devoted themselves to the manufacture of engines for steamboats.

Up to the year 1814, marine engines had been all applied singly in the vessel; but in this year Boulton and Watt first applied two condensing engines, connected by cranks set at right angles on the shaft, to propel a steamer on the Clyde.

Since then, nearly all steamers are fitted with two engines.
In making this important improvement, the firm were materially aided by the mechanical genius of William Murdock, and also of Mr.Brown, then an assistant, but afterwards a member of the firm.
In order to carry on a set of experiments with respect to the most improved form of marine engine, Boulton and Watt purchased the Caledonia, a Scotch boat built on the Clyde by James Wood and Co., of Port Glasgow.