To spill the sail, ease the mainsheet fully and drop the traveller to leeward. To fill the sail, grab the falls of the mainsheet and lean back.
To judge the approach angle when there is little or no stream, sail past the mooring with the wind just aft of the beam. Tack onto your final approach, and the wind will be just forward of the beam (a close reach).
Windward Pick Up
It is much easier and safer to pick up the buoy from the windward side so that it does not go under the boat.