Autonomous Solar Tow Boat
This looks legit, despite some idiotic live commentary from the user/builder. Apparently in Seattle, this small solar model boat tows its owner 20 miles (?) through various waterways, steering autonomously. I guess depending on how big the onboard battery is and how fast you go, anything is possible. IIRC both PhiPi and Ken have built electric boats at some point, so this may be of general interest.