Boonsiri Bangkok on Tanee Road near Khao San road. You can either take the ARL or BTS to Phaya Thai Station and then get a Taxi to the offices of the ferry company on 62 Tanee Road taladyod , Pranakorn, Bangkok 10200. The Taxi fare is approximately THB100, journey time average of 20 minutes. However if you're in a hurry then a Taxi from the Airport directly to the offices could cost around THB 1000.