25/43 His patent for a "spiral propeller," was taken out in July 1836. This was the invention, to exhibit which he had a vessel constructed, of about 40 feet long, with two propellers, each of 5 feet 3 inches diameter. She moved at a speed of about ten miles an hour. She was able to tow vessels of 140 tons burthen at the rate of seven miles an hour. Perceiving the peculiar and admirable fitness of the screw-propeller for ships of war, Ericsson invited the Lords of the Admiralty to take an excursion in tow of his experimental boat. |