Following his earlier successes with 6 and three eights inch by 6 inch stroke 38 indicated horsepower simple high-pressure marine engines for the Admiralty's 37 foot open pinnaces Edward Plenty was asked by the Admiralty to design an 80 indicated horsepower engine for their new 39 foot pinnace. The engine had to be capable of running at full speed for three hours and the whole of the machinery, including the water in the boiler and condenser was to weigh no more than 3 and a half tons. He designed a six and one eights inch by nine inch by nine and three eighths inch (2) 93 indicated horsepower inverted-vertical double-acting triple-expansion surface-condensing marine engine operating at 500 revolutions per minute, and built it at Plenty and Sons works at Newbury. During the Admiralty trials in Stokes Bay the engine's performance exceeded the Admiralty's expectations, running at an average of 502.05 revolutions per minute for three hours.