I found a passenger list for the "Kestral" leaving Port of Fremantle to Sydney NSW 31st March 1866.
I looked for the Stearn name but no luck,then thought maybe they changed their name (because he was a convict ) so looked for a William & Catherine & found them under the name of Fibbs with a William has to be their son William born 1866 but never been able to find where he was born, either here in WA or on board ship? I have contact with William Jnr grandson who lives in Adelaide who has never been able to find his birth either. Thank you for suggesting looking up the"Kestral"