First, truth in disclosure; I own a Miltech AIS receiver, 2 KW Raymarine radar and an E systems chart plotter. I’ve also been sailing SF Bay and NorCal for the past thirty years (I started when I was two
There is no easy answer to your question. SFBoatingdotcom has a link to Miltech’s real-time AIS plot of the Bay where you can see that there is a tremendous amount of large ship traffic on the Bay at any one time. I like the data feature of AIS which displays ships name, destination, ETA and speed & heading. The E system also predicts the closest point of approach in both time and distance. This is handy for me as Freya is berthed in the Oakland Estuary and I want to know if I will have a crossing situation inside the narrow confines of the Estuary (think the turning basin!) This is much more valuable than listening to VTS on the VHF. Also, we tend to spend a lot of time in the ship channel as we sail homeward. The other place where it pays off is in the SF approach channel. Again, knowing what is soon to be coming your way is a godsend.
I like RADAR too. Used it last when coming home from the 3BF in the dark. Very helpful in tracking the 50-60 sailboats returning to their various marinas. The only downside was nobody had their reflectors up and I had to us the quarter or eighth mile scale to pick up reasonable returns which unfortunately, meant I couldn’t see long range to detect a fast moving container ship. My little 2KW transmitter isn’t big enough to do reliable navigation on its own. There simply isn’t enough resolution to accurately paint a coastline or other land features. Here in Cali, I’d stick with the chart plotter. In Mexico, use your copy of Charlie’s Chart’s to augment your paper ones. Better yet, get a set of accurate waypoints from your cruiser friends. The E System’s overlay feature is great as I could readily tell the difference between a channel buoy and a boat. The last two times I’ve been to Half Moon Bay, I used a Radar approach along with the chart plotter. The added benefit was I could “see” beyond the breakwater and into the anchorage. Will everybody displaying their RADAR reflectors, it was easy to figure out the open spaces in the crowded (Labor Day) holiday anchorage.
Fishing boats might be a problem in other areas, but with the declining fisheries (fewer boats) and our normal sea states allowing them only to motor between 10 and 15kts, these are not so much a problem here. Besides they tend to fish pretty far offshore so you only encounter them coming and going. I have had many more near misses with whales than with fishing boats. Our local crab fishermen use old, small fenders as floats and my RADAR will never pick them up. I just try to avoid following the 96 foot (16 fathom) contour as this seems to be a favorite trap line.
After Clinton declared the Central California Coast a marine sanctuary, all the large ships must transit outside of it so all that you will encounter going down to Catalina is other small craft working north and south. RADAR here is helpful, AIS is not. When we went to Hawaii last year we used AIS exclusively as it only consumed about 1 AH where the radar was much more than that plus you had to run the display. At sea AIS rocks! It reliably identified targets of concern and when we called them up on the VHF, we were able to hail them by name.