Why no ferries between Australia and New Zealand?
There are no ferries between New Zealand and Australia because there is no demand for what would be a relatively long boat ride on the open ocean. The distance is approximately 2100km (1300 miles) at the appropriate points, which would take a day and a half for the fastest of modern ferries nonstop, without factoring in the strong tides and sometimes heavy seas. It is far easier to take a plane.