I have owned boats in Calif. most of my life. There is a way if you are not a California resident, and keep the boat out of state for 6 months (when I last checked) to avoid sales tax. For example a friend whose residence is in Arizona, purchased a boat in Florida, and had it shipped to Enseneda Mexico, where it has stayed for 6 months. He took delivary out of Calif. and kept the boat out of the state for 6 months. When he brings the boat into San Diego County he will have to pay personal Property tax on that boat according to what the county appraiser says it is worth. The appeals process is to the county appraiser--and you have a bias against you.
I got caught a few years ago--had purchased the C Dory 25, in New Jersey (from a private party) and kept it out of the state, I thought for the 6 months--however, it was a couple of days shy, because of the change of the law from a year to 6 months out of the state. So I paid the 8% calif. Sales tax based on the bill of sale. However Orange County CA, wanted personal property tax (the boat was in a storage yard) based on their value, not what I paid for it. There was a minor compromise, but I paid 90% of what they wanted--and their value was twice what I paid for the boat.
I had a Cal 46, which I had paid sales tax on in Calif. In a slip in Sequim. At that time I was a Florida Resident, and had to prove to the state of Washington that I had paid California Sales tax. If the boat was in Washington more than 3 months, I had to pay a tax to the state of Washington of about $300--no matter that I was not a resident. Things seem a bit different currently; See:
http://dor.wa.gov/docs/Pubs/WatercraftVesselTax/BoatBroc.pdf
This seems to mostly involve boats more than 30 feet in length where an exemption from use tax is given.
If you take a boat out of Calif, be sure that you document where it is by registration of the boat in another state or country. If it remains home ported or registered in Calif. They will come after you for yearly personal property taxes.