c1843 Her engine was built by Forrester; it had cylinders of 42in. diameter and 4ft. 6in. stroke, delivering about 200 nominal horse-power.[1]
1843 'THE NEW IRON STEAM-SHIP "HELEN MACGREGOR." We noticed the launching of this ship in our paper of the 18th of July, as one of a class that, though intended only for the merchant service, would add to the celebrity of Mr. Laird, iron ship builder, of our port, of whose construction, of the same approved material, she was the 45th vessel. She has since received her engines, and will shortly take her departure for her destination. She was built for Mr. Gee, an enterprising merchant and promoter of steam navigation in Hull, and is intended to run, with goods and passengers, between that port and Hamburgh. Her admeasurement is nearly 600 tons; her length of keel being 180 feet, her beam 26 feet, and her depth of hold 16 feet. She is of extraordinary strength throughout in her plates, ribs, and fastenings; and further secured by four water-tight bulkheads, dividing her into five compartments. In model she is quite equal to our best merchant steamers, and has already proved herself a very fast vessel. The engines, of 230 horse power, are upon a new principle, patented by our townsmen, Messrs. Geo. Forrester and Co., and which combines economy of fuel and reduction of weight beyond any plan yet adopted. She has four cylinders — to each engine — inverted; or, in other words, the cylinders are raised from the bottom of the vessel, and the piston-rods work from below. The four cylinders are placed in a line across the vessel, and a cross beam is connected with each respective pair of piston-rods (starboard and larboard), to the middle of which is attached the connecting rod, giving motion to the crank. The beams below are double, but light, and so contrived as permit the parallel motion of the several rods. The boilers are interiorly of the tubular kind, producing great generation of steam within a small space, and the whole is so compact as to afford much more room for cargo than the usual place will admit. ..... The healths of the chairman, of the East India Company, and his brother directors, of Mr. Gee, the enterprising owner of the vessel, of Mr. Laird and of Mr. Hicks, builder of the engines, were drunk with great cordiality. — Liverpool Standard.'[2]
See here for a description and drawing of the engine by Benjamin Hick, the inventor.
See The Engineer 1890/08/29 p.169 for a drawing of the engine of this ship erroneously attributed as Maudslay's engine for HMS Dee.