With all the talk about generators, I wonder what ever happened to the free piston linear generators touted a generation ago. For those unfamiliar with the concept, a free piston generator is like one of those "shake to get a light" flashlights heavily advertized on TV. Imagine a cylinder closed at both ends with a free floating piston in the center. The closed ends of the cylinder have a sparkplug and fuel injector just like a normal gasoline engine. The center of the piston has a strong permanent magnet. Around the center of the cylinder is a coil of wire. To start the generator a strong electrical pulse is applied to the coil. This pulls the piston to one end of the cylinder as in a solenoid, compressing the air. Fuel is injected in and a spark is triggered. The explosion drives the piston to the other end of the cylinder where the process is repeated. The combustion air and exhaust enter and exit through ports near the midpoint of the cylinder just like a two cycle engine. The magnet in the oscillating piston moves back and forth through the coil, generating an AC current. Diesel versions were also proposed and I suppose some were made. The purported advantages of the free piston generator were light weight, simplicity, compactness, and high efficiency. Most of these features were gained by the elimination of the crankcase, crankshaft, and connecting rods of a conventional engine. The disadvantages were rarely talked about but I imagine that one was the variable frequency AC output. This might have been difficult to deal with in the '50s but with today's solid state inverters it might be easy to handle. I know that some units were made for the military but does anyone know if they are being developed for the civilian market? An efficient, compact, lightweight generator might be just this thing for the boating market. Larry Z