They've had it forever. Tie a rope to the wheel. Presto. Autopilot.

They've technically had autopilots for over a century, the first one was the oil tanker J.A Moffett in 1920. Though the main purpose of it is to keep the vessel going dead straight as otherwise wind and currents turn it, so using modern car terms I think it would be more accurate to say they have lane assist? Commercial ones can often do waypoint navigation, following a set route on a map, but I don't think that's very common on personal vessels.