It's different from state to state but the following companies will cover the boat in regattas:

U.S. Sailing's one design insurance available through Gowrie, Barden, & Brett - http://www.ussailing.com/membership/insurance/#One-DesignInsurance (boat must be on pre-approved 'one design' list)

State Farm (probably dependant on your current level of insurance with them - All my insurance is (was) with them)

Progressive (this was who I went with)

Boat U.S. (who never called me back)