Parsons were clearly involved with marine engines from early in its history. In the 1905 motor boat trials at Southampton it entered a 28 foot boat propelled by its own twin cylinder petrol/paraffin engine rated at 14/16HP. At the 1907 Olympia Boat Show they showed a 7HP motor "with patent valve gear for petrol, heavy oil or alcohol". Harry Parsons generated many patents during his working life, the earliest in 1893, and the last in 1941. As would be expected from his employment history these mainly covered mechanical inventions for pedal cycles and for internal combustion engines. He had some unorthodox ideas about the benefits of concentric inlet and exhaust valves, which may have been a feature of his earliest engines. These inventions enabled the use of alternative fuels to petrol, which presented considerable dangers on a boat due to its volatility. This issue was overcome with the arrival of marine diesel engines (oil engines). He also patented his designs for the marine gearbox, which became a significant product of his company. Parsons continued engine manufacture during WW1, and the 1917 Red Book listing available products shows them to have a line-up of 11 different marine engines all suited to petrol or paraffin. In January 1925 Parsons Motor Co reported that its new lifeboats were ready to be supplied to liners following the new board of trade rules that required every liner having 15 lifeboats to have one powered lifeboat with wireless and searchlight, and every liner with 20 or more lifeboats to carry two powered lifeboats. The Parsons-powered lifeboats had exceeded the minimum speed requirement by 1 knot. Parsons changed its name to Parsons Oil Engines by January 1927, and while indicating the move from petrol to oil engines, this might also mark the move from engine manufacturer to engine conversion for marine use. Parsons does not appear as a marine engine manufacturer in the trade directories of the mid-1930s onwards. On the other hand Parsons marine reverse and reducing gearboxes receive several mentions, being standard fitment on
McClaren marine engines, and optional on many others from the 1930s onwards. In the 1950s Parson's were able to list a wide range of diesel marine engines, claiming in 1956 50 years of experience with marine engines. Most of the engines advertised were stated to be marinised versions of diesel engines from other manufacturers, particularly from Ford, but also from Armstrong-Whitworth, Meadows, and Petter. They continued to list marine gearboxes and also listed steering gear. ==Locomotive Engines==