This took some Wiki sleuthing, but this is what I learned.
The Dunbar was a fully rigged ship launched in 1853 and used on the London- Sydney route as a large cargo and passenger ship. On August 20th, 1857 she was driven onto the rocks at the entrance to Sydney Harbor. The sole survivor was crew member James Johnson.
The SS Cawarra was a paddle-wheel steamship that foundered in a storm in Newcastle harbor, NSW on July 12, 1866. There was only one survivor, who was rescued by a small boat manned by the light-house keeper and his assistant, James Johnson.