The airplane was substantially damaged when it departed the runway (2,555 feet by 100 feet, turf) during landing and encountered an irrigation ditch. The pilot reported that after takeoff he intended to track a Very-High-Frequency Omni Range (VOR) navigation station to an intermediate fuel stop before continuing to his final destination. About 4 hours into the flight he attempted to contact air traffic control in order to verify his position; however, he was unable to establish contact. At that point, he began "to lose confidence in [his] present position" and decided to establish a heading he believed was toward his intermediate fuel stop. After an additional hour of flight, he became concerned about his remaining fuel and contacted a Flight Service Station (FSS). He informed them that he was "lost and short on fuel." The FSS located the flight and provided vectors to a nearby alternate airport. Upon landing at the alternate airport "the aircraft went into a skid, hit a runway cone and came to a stop across from the end of the runway. Just a few feet beyond [an] irrigation ditch." The pilot noted that he did not have experience landing on grass runways. The pilot did not indicate any failures or malfunctions associated with the aircraft's flight control system or engine. He did note the possibility of an "intermittent radio transmission failure" as a possible factor contributing to his becoming lost prior to the accident.