We are expecting 20 year low temperatures in the San Fancisco Bay area later this week. Near the bay it is expected to go a few below freezing for a few days.My boat is in the water. I have no experience regarding at what temperature/duration of lows I should be concerned. I would also like to know if some kind of "lite winterization" is appropriate e.g never mind the water tanks, just drain the pipes.Thanks,John Brecher