The Maine State Ferry Service will likely eliminate the flat-rate ticket structure that has generated frustration among islanders during the past year, according to a proposal released by the Maine Department of Transportation earlier this month. The proposal comes more than a year after the Maine DOT — which operates the ferry service — implemented the flat-rate structure, which more than doubled the ticket costs for residents of Islesboro, one of seven island communities the state ferries serve. Last fall, after a lawsuit was filed by residents of Islesboro, state transportation officials renewed the rate-setting process through formal rulemaking. To keep the rulemaking process going, a preliminary proposal was introduced this spring.