Hold on:
There is ANOTHER ferry operator between Salerno and Positano:
www.coopsantandrea.comThis operator is MORE CONVENIENT than Metro del Mare because the ferry departs from the pier off of Piazza della Concordia, 400 yards from the train station, instead of from the Manfredi Pier clear across town (1.5 kilometers from train station), near the Jolly Hotel.
This operator has sailings even in periods when Metro del Mare is not operating, so be sure to check its schedules online.
Bear in mind that sailings are subject to cancellation due to bad weather. In that case, there is always the hourly SITA bus departing from directly outside the train station. You must CHANGE buses in Amalfi. Buses operate year-round, including on Sundays, even in bad weather (unless the road is closed for mudslides!)
Ferry to Positano: 6 Euros (stops briefly in Amalfi)
Buses to Positano: 3.10 Euros with a change in Amalfi
www.sita-on-line.it