There are 3 ferry companies that do STT to Roadtown. Roadtown FAst Ferrry, Smiths Ferry and Native sun. All three have their own web sites which show the days and times they run that route. You need to look at each ferry companies site to find the times and days you want. Before you buy make sure you want their tickets as the tickets are non-refundable and non-transferrable to the other ferry. I suggest you do not buy tickets until you are at the ferry dock especially if you have a tight connection.