Have a look at National Australian Archives (not that it helps with the ship on which the 'Cavill's' arrived.http://www.naa.gov.au/collection/recordsearch.aspx
go to search now as guest, in in Keyword, put Cavill, Frederick.
you get 5 results.
1 Correspondence with applicant Frederick Cavill concerning invention entitled - Improved floating swimming baths
3 Cavill Frederick Charles : SERN 2008 : POB Sydney NSW : POE Holsworthy NSW : NOK M Steward Helen
very interesting reading.