The Sea Shepherd Conservation Society has accused a Japanese vessel of ramming its anti-whaling protest boat.
It said a Japanese security boat rammed its high-tech $1.4m protest boat, the Ady Gil.
Japan's Fisheries Agency said the collision happened when the Ady Gil suddenly slowed in front of the Japanese vessel.
Sea Shepherd's founder Paul Watson, insists it was a deliberate move.
The Sea Shepherd's anti-whaling activists are protesting the activities of a government backed Japanese whaling fleet. Japan defends this limited whaling as a cultural tradition.
Six crew on board the trimaran were rescued and are now on board another vessel, the Bob Barker.