This could be done because there was no skeg.
"The Migrations of an American Boat Type"
Howard I. Chapelle
If a sharpie had a skeg, it was possible to use one sail without shifting the mast, but at a great sacrifice in general maneuverability.
"The Migrations of an American Boat Type"
Howard I. Chapelle
The other end of the propeller-shaft rests in the skeg bearing.
"Boys' Book of Model Boats"
Raymond Francis Yates