The boat ride isn't that much fun and also you could be waiting at POFQ for a boat for awhile as it gets two thirds full at POR the first stop.
You can take a boat at DS from marketplace to the west side if you want a boat trip, there are also cute car boats that go out into the river (would have to pay) at the new Boatshed restaurant, you don't need to eat there.
Taking the bus two and from DS is a bit of a pain, buses are fewer, the trip is unnecessarily long as they take you around the back. The new orange car park at DS is amazing, if you have a car drive there.