Currents & tides
Watch your tide tables. The tide affects the current all the way to Portland and reverses the current as far up as St. Helens. Heading up river, the only way for a sailboat to make miles is on the flood - you can chase it up river very nicely. The Columbia bar is especially dangerous on an ebb.
Explore the sloughs
The backwaters are some of the prettiest (if shallowest) places - I especially liked rowing the dingy into those behind Cathlamet. The islands between the Cathlamet area and Tongue Point are a state game refuge and have specific rules regarding them. However, the area is large, beautiful...and shallow.
Rafting to Log booms
A common practice on the Columbia is to tie to log booms anchored in the side channels. We could not figure out how to place fenders against mostly submerged logs. Here's one trick: get some of those fenders with the needle-valve AND a screw-in cap over the valve. Punch out the valve. Fill the fender with water. Replace the cap. The fender will now hang under the water & not ride up over the log.
Another solution, supplied by Jeff Antinoja of Kalama, WA:
make your own fenders out of a hose called spyrallite. It has a
wall thickness of about 1/4 inch, sinks on its own and is clear
so it will not scuff the side of your boat. It is rigid so it can
be used for the suction hose on diaphram type sump pumps and not
collapse. The 3" size runs a couple of dollars per foot. If
you can't find it, contact Jeff at firstname.lastname@example.org.
Here is what you do: take about a 2' to 3' section of this hose (3" diameter is perfect) and drill about a 1/2" hole in it about 1" down from the top, then attach the rope (line-3'-4'), then you put the fender over the side and it will sink, but you want to leave about 6" to 1' above the water. Tie the line off and"presto" a very effective, lightweight, lograft fender that also works well for rafting to other boats!
Portland Area Bridges
Check the charts carefully for heights. The railroad bridges only respond on VHF channel 13 - if you try and contact them via ch 16 (per the Coast Pilot) the Coast Guard will correct you. You will have the best luck contacting the railroad bridges by VHF if you use their preferred names:
"Vancouver railroad bridge" for the one over the Columbia's main channel at Vancouver, WA
"North Portland Channel railroad bridge" for the one over the North Portland channel between Hayden Island & the Oregon mainland (note: you have to contact this bridge either by phone or thru the Vancouver bridge one hour before you need it opened - there is no bridge tender otherwise)
"Saint John's railroad bridge" for the lower Willamette bridge. BTW, Carl H. claims that you can get better response from this bridge by have a woman crewmember call. Can't vouch for this myself but it seems to be the kind of knowledge that everyone needs.