Heres something scary to consider when thinking of using boats for kite/rider rescue, how to correctly approach a downed kite (as dave........mentioned).
A mate (non kiter) told me of a bunch of guys he saw in spain trying to retrieve a downed kite by boat. conditions were 25 - 30kts open surf beach, near tarifa. The kite was tumbling along lines and bar slopping around behind the kite getting twisted up yada yada, these guys came up from down wind, turned side on to the wind, to grab the kite as it rolled towards them. They pulled it on board but the wind caught it and it rolled out the other side. The bar and lines then got caught on something on the boat and the kite hot launched and swung into an almighty suicide kite loop. The boat and all its passengers and everything inside got emptied into the churning surf. Kite crashed and dragged the boat to shore 500m down the beach.
Dont know if after this story i would really want to use my boat to rescue a downed kite, specially not in 30 knots and churning surf.
Then again i'm not a crazy spanish dude