The patent on the Australian designed and manufactured inboard marine engine, Chapman Pup, was held by the Erskineville (NSW) based company, Chapman and Cherak.
This twin cylinder, two stroke, engine was made in Western Australia, under license, by the Perth company, Harris-Scarfe and Sandovers Ltd in 1930.
The Chapman was a popular small engine in the 1930s, and its design was reputedly based upon a French engine. This early engine had a crankcase which ran the length of the motor, producing a large surface area which did not seal well, reducing the pressure and making it difficult to start.
Engineer, Tommy Overgaard, changed the configuration of the crankcase to a pear shape, altered the rotation of the engine and highly improved the compression ratio in the crankcase.
Overgaard also introduced a portable magneto which could be slipped on and off and taken away from the moist environment while the engine was not in use.