How do you move the windmill on Astro Knights Island?

To open the roof dome on the mill (where the hovercraft is kept), first go inide and pull the rope that unlocks the mill gears. Then go outside and climb on the windmill arms. Turning them counter-clockwise opens the roof dome. Go inside and use the manure you got from the mill farm. The hovercraft will go to its permanent position in the mud swamp.