It is a custom-made warship without guns, pimped out with bigger engines and a long-distance fuel tank.

Anti-whaling activists Sea Shepherd have a brand new, $12 million custom-built ship they boast will for the first time match the speed and endurance of Japan's whaling fleet.

And with Japan's defiance of an international court ruling about to be in the spotlight at a global summit next month, the activists plan to sail the new vessel to Australia, before launching south in a bid to disrupt the summer whale hunt near Antarctica.

"Our biggest challenge in our campaigns in the past has been that the Japanese whaling vessels have rammed us with their superior size, and they have outrun us with their superior speed," Sea Shepherd's Peter Hammarstedt told Fairfax Media.