Hi Michelle,
I have most of the brochures for Fairstar from 1979 onwards, unfortunately not for 1983. I do have 1984 though, however Fairstar did not do an 18-night cruise at that year, perhaps it was 16-nights and you just partied like it was 18! In any case the cruises in September/October 1984 were:
September 9th - Sydney - Boulari-Havannah Passage - Vila - Lautoka - Suva - Bounty Passage - Taunga - Nukualofa - Matthew Island - Noumea - Sydney (16-Nights)
September 25th - Sydney - Amadee - Noumea - Isle of Pines - Mystery Island - Tana Island - Vila - Havannah-Boulari Passage - Sydney (12-Nights)
October 7th - Sydney - Boulari-Havannah Passage - Vila - Suva - Bounty Passage -Taunga Island - Nukualofa - Matthew Island - Noumea - Sydney (15-Nights)
October 22nd - Sydney - Noumea - Tana Island - Vila - Suva - Dravuni Island - Lautoka - Sydney (14-Nights)
Interesting to note that each cruise has a number of 'sail-bys' - Boulari-Havannah Passage, Bounty Passage, Matthew Island, Tana Island. In the 1980's far more was made of these to pad out a sea day than generally occurs today.
In any case, I hope this assists with at least one of the cruises.
Cheers,
David