Which of the following would not qualify as a covered trailer when being towed by an automobile?

In the context of an automobile insurance policy, a covered trailer is typically defined as a trailer designed for use with a vehicle, usually for the purpose of transporting goods or personal items. Among the provided options, a U-Haul trailer fits this description as it is specifically designed for transporting belongings and is intended to be towed by an automobile.

A sailboat, while it can be towed, is more of a recreational vehicle rather than a trailer used for general transport. It is not typically covered under standard automobile insurance unless specified. Farm wagons or implements are also not classified as trailers designed for everyday transport with a personal vehicle; they function primarily in agricultural settings and do not meet the standard coverage requirements for auto insurance.

The answer indicating that "all are covered trailers" does not hold since the classifications of sailboats and farm implements do not meet the criteria set forth for covered trailers in automobile insurance policies. Therefore, they do not qualify under the typical definition used in such insurance contexts.