Take a look at where you might want to go as some of the places that the ferry stops don't have roads leaving them at all.
The ferry seems slooooow to me and there ain't much to do on it. Bring a book or two. You'll find yourself wondering if your bike is laying on it's side skidding around on the below deck for the first while. Not to worry though... you can't go make sure anyway.
Btw... it's a great idea.