Electric ferry operators from Denmark, Maine and Washington state shared their experiences Friday in a half-day public conference aimed at encouraging the Steamship Authority to begin reducing dependency on fossil fuel.

Electric-powered Steamship Authority ferries are a long and very costly way off, according to a marine study by boat line consultants.

Three of the Steamship Authority’s four freight ferries — the Gay Head, Katama and Sankaty — will need to be replaced within the next three to five years, a marine survey has found.