To get into VRS you need to be travelling downwards at over half the speed of your downwash and an S61 has far more than 600'/min downwash, more like 2000'/min.
It is all about disc loading - older helicopters had low downwash speeds because engine power was lower and the rotor had to be bigger.
Modern helos have very powerful engines and smaller rotors for the same or increased AUM.
Nick Lappos published a RoD vs Fwd speed diagram for VRS produced, I think, by the US Army. The VRS boundary was related to downwash speed - you needed 0.6 to 0.8 of your downwash speed to catch it up enough to start to ingest it.
https://www.rotorandwing.com/2011/11...wash-velocity/
Well I can tell you from experience that the 61 can and will get into VRS at WAY less than 1000 ROD. I was shown this during my initial endorsement over 30 years ago. The instructor simply said climb up to 6000 ft, this near a coastal city and a hazy day so no real discernible horizon. Then he said come to a hover. I brought the nose up lowered the collective just as you normally would. As I was coming to but not quite to zero AS I noticed a slight ROD maybe between 300 to 500' ROD and I just added a bit of collective. Well in a split second we were coming out of the sky like the preverbal greased manhole cover. The instructor pushed the cyclic full forward so we were then looking outside thru the skylights. He said he hates doing that but wanted me to see just how easy it was to get the old girl into VRS. So, as Mr. Prouty said 300' ROD because the S61 is NOT a modern helicopter. Size and gross weight have no bearing on VRS, actually the 2 times I have been in it it was both times in an empty a/c.
Anyway, this has been beat to death......let it die.