There are two ways to travel from Ernakulam to Mattancherry by public transport : Ferry and Bus.
Mattancherry Ferry Route
The second option is to take a ferry from Ernakulam to Mattancherry. This is the shortest route (about 20 minutes). A boat leaves typically every 15-30 minutes.
There are two ferry points at Ernakulam. Boats for Fort Kochi and Mattancherry leaves from the Ernakulam Boat Jetty near Subash Park (at the south end of the Marine Drive at Kochi).
There is a ticket counter at the ferry terminal building. You'll see the ticket queue once enter the ferry building. Go to the left side counter. Ernakulam to Mattancherry ferry ticket cost Rs7. The ferry route is via Fort Cochin and Willingdon Island (Embarkation Ferry).
City Bus in Ernakulam