Liability insurance is important. Along with liability medical insurance, lost property, uninsured boater. For a boat this size check your homeowners policy. Adding it under the homeowners may be the most economical solution.
Depending on what you paid for the boat, hull insurance is a toss up. If you paid cash and the boat is totaled, you're out the money you paid. If there is a loan and a lien on the boat, then the bank is going to want hull insurance.
Don't forget get towing coverage for traveling on the road. A flat tire can cause a lot of damage when the trailer goes out of control. Check your auto insurance for coverage.
BoatUS usually has very reasonable rates and if nothing else is a good source of information on insurance.