Bursa Deniz Otobüsleri (BUDO) runs seabus passenger-only fast catamaran ferries between Istanbul's Eminönü and Sirkeci ferry docks and Bursa's Mudanya docks 7 or 8 times daily, making the voyage in two hours (map) for TL29 one-way/single.
In summer, there may be more frequent voyages.
Reserving Your Seat
Tickets bought online may be one lira cheaper than those bought at the dock.
For buying tickets, the BUDO website is clear and easy to use, with an English-language version. You enter your Turkish mobile phone number or your email address to reserve a seat and buy a BUDO ticket online. Notices regarding your reservation and ticket will be sent to your Turkish mobile phone or to your email address, so be sure it is correct.
Getting Your Ticket
If you succeed in making a reservation and paying for your seat, you will print your ticket from a machine at the ferry dock. To print your ticket, you must have the same credit card that you used to make your reservation online, and you must have your PNR(6-digit alphanumeric reservation code). Without them you will be unable to obtain your ticket.
If you can't buy a ticket online, you can ask my friends at Efendi Travel for help, or you can go to the Eminönü or Sirkeci Ferry Docks in Istanbul to buy your ticket.
The BUDO website shows seat availability, so you can see if a voyage is heavily booked or already sold out. If it is not, you can try going to the dock, ready to travel, 30 to 60 minutes before departure time. In most cases, you should be able to get on the boat.
Ferry Dock to Bursa Transport
After debarking at Mudanya, look for the yellow city buses that will take you to the Güzelyalı docks, the city center, and the intercity bus terminal. More...
From Bursa, you can catch an onward bus to anywhere in the Aegean region (map), and indeed anywhere in Turkey.
—by Tom Brosnahan