And starting January 1, 2027, Illinois boat owners with a motor over 50 horsepower — or a vessel 21 feet or longer — will need liability insurance to legally put that boat in the water. It applies to boats with engines of at least 50 horsepower, or boats that are 21 feet or longer. Only about 13 states required some form of recreational boat insurance before this law passed. What Liability Insurance for a Boat Actually CostsFor most recreational motorboats, boat liability insurance runs between $150 and $500 per year. Most major carriers that write auto and homeowners policies in Illinois also write boat insurance.