...not sure about prawns, but helicopters are used to herd tuna!
As far as the fully articulated 2-bladed rotor system, (as mentioned already) it isn't needed, although you will see coning hinges on Robinson rotorheads - this because the blades are not designed to absorb the bending loads of coning. (There has been and continues to be debate about the possible negative effects of having both a teetering and coning hinge on a rotor system and its contribution to certain unexplained inflight breakups of Robinson helicopters.)