The captain of a Washington state ferry that ran aground 100 feet from the Keystone shore misjudged distance and the effect of the current, Washington State Ferries has concluded.

William Chapple, a 5-year veteran of the Port Townsend-Keystone route, ran into fog the morning of Aug. 22 and thought he had 1,200 feet of visibility. In fact, he had only 600 feet of visibility, an internal investigation found.

“He’s one of our best. He just found himself in a bad situation,” said Joe Nortz, the ferry system’s director of operations.

The error led to the 75-car ferry Quinault running aground and 107 passengers being stranded aboard for nearly six hours before a tugboat and a rising tide freed the vessel to resume service.

Chapple received a letter of discipline, Nortz said.

The ferry system is studying whether the Keystone terminal should be moved, since many sailings are canceled each year because of tides, strong currents and fog. State Ferries officials are expected to make a decision this fall.