Patrick Ellam had cruised extensively in Theta, a 15 sq. metre centerboard sharpie; a sailing canoe in which he had crossed the English Channel on numerous occasions. He concluded that a very small boat could handle open water if handled properly

Sopranino’s size was specifically chosen so that two men, with provisions, could undertake a hundred mile or more leg of a race or cruise in relative comfort, but was still to be such that could be trailed behind a car.  This latter requirement placed considerable restrictions on her size and weight. She was designed to plane and so her displacement was kept as light as possible, but while beam appeared to be narrow for a boat intended to plane it was essential to reduce drag and maintain momentum in the typical choppy sea prevalent in the Channel.

Not surprisingly many of Sopranino’s design features were unique. Some ideas were borrowed from model yacht design; for example rather than merely building a swing or lifting keel the design included a separate rudder hung on a skeg and removable fin and bulb keel, features which were later to become commonplace on the small craft and ultimately yachts of all types and sizes.