This past week I had a chance to make a days passage from Stockton Calif. to Alameda....just south of Oakland on a 50 yacht. Ok, this is August, and I froze my ass off. For the love of God, lots of boats, Golden Gate bridge, Alcatraz et all, but not one bikini, no hotties, just boaters in jackets....no way, no how. I love all you bay area boaters, but if you can't swim in it, sun in it and love the water....I have to stick to warmer shores.... there was not enough hot rum to get me back on those waters....party on.
The San Francisco Bay can be a bit brisk as you discovered. If you go just a bit inland though, the temperatures generally rise about a degree per mile. I noticed about a 25 degree difference between Stockton and SF on the same day which is not unusual. The Sacramento Delta area is pretty nice for boaters since it offers thousands of miles of cruising areas. The boats of choice seems to be houseboats though.