The transfer of the Arran ferry from Ardrossan to Troon would cost the public purse a massive £166 million over the next 30 years, according to a report drawn up by North Ayrshire Council.
Ardrossan is campaigning to retain the 180-yearold ferry route following an attempt by Associated British Ports to shift the service to Troon.
North Ayrshire Council and Peel Ports, the operator of Ardrossan Harbour, have now submitted their financial case to Transport Minister Humza Yousaf, who is expected to make a decision in the next few months on the future of the route.