Tax is due in the state of California IF the boat
is brought into the state prior to a 6 month period. Yearly tax (property) is figured on the first day of January no matter when you brought it in or how long it will be here.
If your boat is documented outside the state and your just passing through, which sounds like you are, there's no tax due...
Unless you plan on documenting within the state, you'll then have to pay..