Having thought about this before I posted the question, I too thought like Mighty Gem that the Heli could possibly skid across the water, due to the lack of grip compared with say soil.sand,grass or tarmac, unless the Heli was some how tethered,
My reasoning for this is the way that Helis start to spin on the water untill tail rotor authority is available on start up, that spinning shows lack of friction, to what less extent I don't know.
PeterR-b