The new Sea Shepherd trimaran Ady Gil has docked in Hobart for maintenance ahead of its anti-whaling mission in the Southern Ocean.

The trimaran leaves on Monday to join Sea Shepherd's flag ship Steve Irwin in the Antarctic.

Captain Pete Bethune says the Ady Gil looks similar to a spaceship and is well designed to keep pace with Japanese whaling vessels.

"It holds the record for a powerboat to circle the globe, 60 days all around the world," he said.

"It's a wave piercing boat, its got a very fine bow and a lot of weight in the bow from fuel and when you hit a wave it just punches through rather than riding over the top like a normal boat, extremely efficient vessel we can travel half way around the globe on a tank of fuel.

"It just gives Sea Shepherd another tactical option. The Steve Irwin - their main vessel - is relatively slow and it's unable to keep up with the harpooners whereas this vessel will do up to 40 knots.

"So it's well fast enough to keep up with all of the whaling vessels that are down there."

Captain Bethune says some modifications have been made to the Ady Gil.

"We've added about half a tonne of Kevlar onto the hull to toughen it so it makes it not fully ice proof but it does make it a lot more resilient against ice," he said.

"We've got a special paint that deflects radar signals so it makes it makes it very hard for radar systems to pick us up and a few other things I can't tell you about."