Thanks all
Although there is a wealth of information that has been pointed out to me, for which I am extremely grateful, I still find myself with the same issue.

My great greatgrandfather seems to have dropped off the radar for a few years. I have him as a 5 yr old in the 1861 census in England, then the rest of his family in the 1881 census - nothing in 1871. Then he supposedly appeared in Australia in 1876 (no real evidence), where he crewed on ships between Brisbane and Sydney in 1881 before marrying in SA in 1882.
This has been bugging me for 12 months now.......

ANY clues would be greatly appreciated!
Jacqui