I’ve been out in 8kn and had the thing relaunch easily. Other days I’ve been out in the same kind of wind, and basically had to come back to the beach (like this Saturday, probably less than 8kn, incoming neap tide). The tides/currents can obviously help or hinder the process.
I find that if I can’t self-launch on the beach, I generally won’t be able to relaunch in the water, and factor this in accordingly.
I haven’t tried this on the water yet, but on snow I’ve reversed launched the kite by pulling on both steering lines at the same time. You need to reach up about an arms length and pull from there. The kite will hover a few feet off the snow, then let out one side and the kite will pivot and fly away.
A quick relaunch is possible in 5 - 8 knots as mentioned above by quickly tugging the front lines ... Don’t be shy , pull 1 - 2 feet rapidly & ’ pump ’ your kite into the sky ... It’s like starting a lawn mower & works best with the kite directly downwind. ( before it drops onto the water is best !!! )... If your kite is inverted do the same with the back (outside steering lines) until your kite is high enough off the water to twist it back to flying forward ... This takes practice preferably with a small kite in controlled conditions ... With practice these maneouvers become second nature ... I hope this helps ... 8)
In the really light stuff with big kites I revert to the old school if the kite is LE down. Let the bar all the way out to an arm’s length, and swim at it hard for a few strokes. The kite will start to roll onto its back, at which point you can initiate the relaunch.