Corkie,
Check out the weekend fishing reports for spots.
My suggestion would be to launch at Willamette Park or that ramp under St. Johns bridge. Cruise up to OC and then start working your way down river.
Try all the spots from the Garbage Hole down.
See if you spot fish getting caught, check out what other folks are using (bring those spy glasses!)
As BiteMe Guide Services noted, prawn spinners upriver in the faster, shallower water and then herring if fishing the deeper slower water downriver.
I noticed some of the successful guide boats were working the back edies upriver, where the water shallows up and slows down a bit.
Makes sense that is where fish would be holding, resting out of the strong current.
That also gets you out of the more stressful areas of strong current and Saturday crowds.
Be a nice ride up and down the river, check out a lot of spots, look for the hot spots and a relaxing Saturday fishing...might even get a fish <grin>.
Brion