And if you turn a sail sideways and put it on a spindle with several other sails, you have what looks a whole lot like a propeller. So instead of sailing sidew

And if you turn a sail sideways and put it on a spindle with several other sails, you have what looks a whole lot like a propeller. So instead of sailing sideways so that your air foil sail can move sideways through the wind, the Blackbird harnesses the power of sales moving sideways through the wind while pushing the craft directly into the wind.