Naptha powered yachts

The advent of the steam yacht transformed the yacht market but it was anything but convenient. Expensive to run and maintain, the steam engine required licensing and inspections and required a qualified steam engineer to operate it. In addition, cruising was a slow process, the boiler required time to come up to steam. In the 1880's and 90's, the internal combustion engine was early in development, expensive and not yet at a dependable state.   
In New Jersey a Frank W. Ofeldt was working on his own engine using a oil byproduct, naptha gas. Instead of water, naptha filled the boiler, it was also used as the fuel to heat the boiler. Upon heating, the naphtha rapidly turned to a pressurized gas which was used to act against the pistons in the engine in the same manner as a steam engine. After passing through the cylinder, the gas then went into a pipe under the boat, cooled down and returned to the boiler as a liquid. 
As  pressures were much less than a steam engine, everything could be built lighter and best of all a licensed engineer, licensing and inspections were not required.  The owner-operator could master its operation in a short while using only the manual. 
It seems strange that boiling water would require a licence while boiling gasoline did not. The cost advantages of the the system allowed middle class boaters to own a power boat for the first time and by 1900 there were at least 3000 naptha powered yacht in use. Despite the maturing of the internal combustion engine naptha-powered yachts were still being sold in 1910. 

D.W. Fostle, Speedboat, Mystic Seaport Museum 1988

The original 1885 naptha launch on display in the 1920s.