By degrees these obstacles were overcome, but the questions of the number, size, and shape of the blades, their pitch, or theoretical forward movement in making a complete turn, their degree of immersion and their most efficacious speed, are taxing the brains of the most skilled naval engineers and architects of the present day. Obviously, these questions are of the highest importance to all students of marine engineering no less than to steam-ship owners. As the power of the engines increased other considerations had to receive attention, including the best material for the construction of the propeller and the best methods of building or casting it to stand the enormous strains imposed upon it by the work it had to perform. Almost simultaneously John Ericsson, the famous Swedish inventor, and Francis Pettit Smith, a Middlesex farmer, were engaged in experiments. Mr. (afterwards Sir) F. P. Smith made, in 1836, a clockwork model of a boat with a screw propeller, and it was so successful that he built a steam launch in order to try the experiment on a larger scale. This boat, the _F. P. Smith_, was about 29 feet long and 5 feet 9 inches beam, and was tried in the Paddington Canal in 1837; its power was derived from a steam-engine with a cylinder having a diameter of 6 inches and a stroke of 15 inches. The propeller was of wood with two full turns, and was placed some distance in front of the sternpost, where it was driven by a system of bevel wheels from the engine to the shaft. The propeller lost a blade on one of its trips, thereby adding to the speed of the vessel, and this led Mr. Smith to instal another screw with one turn only, or a half-turn on each blade. A metal propeller was afterwards substituted, and the boat went from London to Folkestone and other places on the coast at an average speed of five to five and a half knots. It is stated Mr. Smith built a vessel of 60 tons[83] which, with a screw propeller, attained a speed of seven or eight miles an hour and went from Blackwall to Margate in eight and a half hours, and that she also towed the _British Queen_ steamer into the West India Dock. This probably refers to the _F. P. Smith_, the assertion that she was of 60 tons being erroneous. The results of the experiment were so satisfactory that a syndicate was formed which took the matter up and brought out the Ship Propeller Company, to whose capital Messrs. Rennie, the shipbuilders, subscribed £2000. [83] _Historic Times_, March 1849.