'Port out starboard home' is a wonderful old urban legend. Sadly, it has, according to the Oxford English Dictionary - the "bible" of word-sources - no basis in fact. Its first use in writing came in a 'Punch' article in 1918. PG Wodehouse had, in 1903, used the word 'push' to mean 'grand' in exactly the way 'posh' is used. Perhaps, therefore, 'posh' is just a corruption of 'push'. Even a publication called the 'Mariners' Mirror' dismissed the passage to/fro India idea decades ago. Also, given the long India-connection, 1918 is just too late for that to be a likely source.