Take over (5)
But I've got no explanation for this one! Could you help me understand?
(Other definitions for ferry that I've seen before include "Transport boat that plies regularly" , "Boat for transferring people across short stretches of water" , "Boat that plies from shore to shore" , "Boat that carries clients across a stretch of water" , "Ship for crossings" .)
'take over' is the definition.
(I know that take over can be written as usurp)
This is all the clue.
(Other definitions for usurp that I've seen before include "Take power unlawfully" , "Take control illegally" , "Seize unlawfully" , "Arrogate" , "Supplant (someone in power)" .)