I see that you are in California..
In California, the owner of a boat on January 1st, documented or otherwise owes the personal property taxes. On a documented boat, you will get a letter from the county where you keep your boat, requesting information. The County Tax Assessor will then send you a bill, payable in full and due no later than August 31st.
The Assessor's Office has dock walkers to check on marinas. Los Angeles County is very active, others might not be as active. Bottom line is some day they will catch up to you.