Sydney Ferries has offered Wi-Fi on its services since February, but when the launch first happened, it didn't include services along the Parramatta River. The good news is that has changed, with Parramatta services now offering free Wi-Fi for travellers as well. The bad news is that the data limits for daily use are being more strictly enforced.
I jumped on a ferry to Meadowbank the other day and was surprised to notice a poster promoting free Wi-Fi, which I hadn't spotted before. A short while later, I was connecting and running speed tests to see how it worked, getting similar results to when I originally tested the service to Manly.
However, my plans to test the speed at every stop were abruptly halted when I hit the 30MB data download limit and was told I couldn't log in on the same device without paying for the service. In my original test, this policy was said to be in place but wasn't actually being enforced; you could log on as many times as you liked. Not any more, it seems. Being an excess gadget carrier, I could have switched to a second device, but I decided not to be greedy.
I'm guessing that the same rule is now applying across the ferry network; if you've found any different, tell us in the comments. Phone signal along the river is pretty reasonable anyway, but if you are commuting via ferry, it's a nice option to have.