A 43-year-old first engine-driver on board a hydrofoil docked at Piraeus was electrocuted shortly before the ship was due to depart for the island of Aegina on Tuesday.
The cause of the accident has not yet been determined, while the captain and first engineer of the vessel have been arrested and will be led before a Piraeus Misdemeanours court prosecutor.
An investigation is being carried out by the coast guard, which has ordered a formal internal inquiry.