Do I need travel insurance for a domestic cruise in Australian waters?
Unless there's a Medicare registered doctor on-board the cruise ship, you won't be able to use your Medicare card if you have to see the doctor. As most cruise ships are owned by American companies, it's unlikely you'll be able to use your Medicare card, which means you'll be charged for the service.
While cruise ships have on-board medical facilities, they may not be equipped to deal with serious medical situations. If this happens, you may need to be evacuated off the ship and taken to a hospital back on land. That's where a cruise travel insurance policy may prove invaluable.