A powered watercraft system including a watercraft body having a propulsion system, a foot swimfin, a sensor configured to measure a value indicative of a manually-generated time-variable first propulsive force resulting from a leg motion to the foot swimfin to move the watercraft body, and a controller configured control the propulsion system to generate a second propulsive force for powering the watercraft body based on the value indicative of the first propulsive force, the generated second propulsive force being at least partially contemporary with the first propulsive force.