This is how it happened. The heli had landed - it was not the normal one Greenpeace used (Normally a 500D) so Things were 'experimental' from the start.
The ship was pitching heavily as you will notice the tail raising with each pitch until on one large pitch the heli gets light on the skids and slides forward towards the hangar. While doing pre wind down checks (from a checklist) pilot looks up to see this meeting about to take place with the hangar when reactions take over to pull the machine off the deck. Obviously collective is hauled up with a little too much aft cyclic and the tail is struck on the deck.The rest is downright lucky.
Cause of the heli sliding forward was the rope used for lashing at the back was burnt through by the exhaust. The guy on the left of the picture tried to jump overboard but his jacket got caught in the net which probably saved his life (freezing water) The rest is history except that the operators learnt one hell of lesson and have subsequently changed operating procedures since getting their usual 500 back.
Good old unfamiliarity rears its ugly head again, thankfully a lesson was learnt with no injuries.