RedactedNarrative: As boat was returning to dock at dusk, the main engine failed. The operator went to use the trolling motor at which time it was noted that water was coming into the boat. Approximately 10 minutes later, the boat went under water and flipped over. The occupants were not wearing life jackets and hung on to the boat. They called for help. A passerby picked them out of the cold water and brought them to shore. It was determined that the water was coming into the boat because the drain plug came out. The boat occupants were cold from being in the water and were warmed up in a warm truck. They did not seek/need medical treatment. The boat is a Total Loss.