Fishermen centralize /au/ and /ai/ more than any other occupational group
(This was subconsciously, in order to establish and identify themselves as Vineyarders, an independent social group rejecting the norms of mainland America which was bought over by the summer holiday makers)
People of the age group 30- 60 tend to centralize diphthongs more than younger or older people
(A move from the standard American norms emerged, particularly in the younger speakers of this bracket between the ages of 31-45, towards a pronunciation associated with the fishermen)
Up-Islanders used the centralized diphthongs more than people living in the area of Down-Island