KiteSurfing...you touch on an interesting subject. I've been wondering about the =/- of using a kite as a sail for a boat.
In PARTICULAR....suppose one were to build a flying wing (perhaps)...very lightweight, with solar cells a battery, and a folding prop....fairly good sized...ten or twenty foot wingspan...launch..but keep it tethered...radio control...when it's up high enough..shut off the prop and let it PULL the boat...