Along the Grand Canal

1. You can get to either dock using the barge -- but not in the same play-through of the story. Once the barge has docked at one of the docks, there's no way to get the barge to the other dock.
2. You should use the barge to get to the dock on the east bank.
3. It has something to do with the barge controls and the river current.
4. Control the barge's speed with the purple button. When the engines are on, the barge will make a wider turn and end up near the east bank. With the engines off, you'll drift around the bend and end up near the west bank.
5. Later, to get to the dock on the west side of the canal, you'll need something from the palace area.
6. Use the raft from the Catacombs. (Teleport to the ruined castle region, put the raft in the water, get in the raft, and drift until you're at Donald Dock or the Abandoned Dock.)