This is great idea. The hexa drone can be equipped with sonar or better heat detection devies to track and find people under water. Moreover speaking of the life rings they can be attached as non inflated tube similar to that of a parachute which opens on release. That would make it possible to carry more than 2 liferings. But the problem with this is that it is needed to made it such a way that it can track and throw rings from a higher height so that the drowning person seeing the copter doesnt grabon to it risking his life and that of hte copter.