Q: I own a boat. What insurance do I need?
A: A boat policy, of course! A boat policy is similar to an auto policy. It provides first party coverage (ie payment in case the boat is damaged) and third party coverage (ie payment if someone is injured because of your use of the boat). You need to find an insurance broker who writes these policies.
In addition, you should be purchasing an umbrella policy. You may need to have your boat policy with your homeowners and auto policy to get an umbrella policy, but check around. Premiums on these things vary widely.