Here's a Google Earth image of Datchet Sailing Club:



The objects arranged on the slopes leading up to the club are dinghies and catamarans, not cars. I think they have storage for about 300+ boats and ample car parking. The reservoir is almost 500 acres when full and is very deep. They usually manage to set a good sized W/L course in the prevailing S. Westerlies and conditions are reasonably steady as the whole pond is raised some 60ft above the surrounding countryside.