If the MBTA withdraws funding for its commuter ferry service - as the cash-strapped agency proposed Jan. 3 - the state should look for other ways to keep the boats that carry 1.3 million commuters afloat. A proposal under consideration at MassDOT would transfer responsibility for the service from the MBTA to Massport, the state agency that runs Logan Airport and the port of Boston. The ferries might be a better fit there anyway.