Sentence:  "You were going faster than the water." "Good thing. That's <WSD>sweepage</WSD>, and it's the only time you've got control. Slow down and you're just wrestling water. Big waves, you've lost <WSD>sweepage</WSD>." 
Meaning of the word marked with <WSD> tags:  The state when a sweepboat is moving faster than the current of the water.