Nick Perrin, 58, was crushed between the MS Oldenburg ferry and the harbour at Ilfracombe, according to a report from the Marine Accident Investigation Branch.
He was lowered into the water but died from his injuries later that day on 3 August 2015.
The ferry carries 267 passengers between north Devon and Lundy Island.
The report said Mr Perrin, an onshore rope-handler, had got on the ferry to drink tea with the crew at around 13:40 BST on 3 August.
The crew was called away to prepare to sail at around 14:00 BST and was not aware of Mr Perrin leaving the saloon by a "shell" door and walking along an outside ledge to steps.
Crewmen heard Mr Perrin cry out and saw him trapped between the ship and a large wooden post.
The report said: "Due to his injuries, they were unable to recover him onto the vessel and he was lowered into the water to facilitate his retrieval by a lifeboat."
Members of the public witnessed the incident and called emergency services.
The Ilfracombe inshore lifeboat pulled Mr Perrin from the water. He was treated by paramedics but pronounced dead just after 16:00 BST.
The report said the ship was probably pushed into the shore by the swell.
An investigation by ferry owners Lundy Company found the incident was caused by Mr Perrin not using the gangway as the recognised method for leaving the ship.
The company has now installed new barriers and signage "to prevent unauthorised use of the doors" used by Mr Perrin.
A shore worker died after he became trapped trying to get off a passenger ferry, it has emerged.