Savings from the scheme, which is due to operate on all Caledonian MacBrayne routes by 2015, will be more than wiped out by ticket price rises, according to the ferry operator's private-sector rival, Western Ferries.
In its submission to the consultation on the Scottish Government's draft ferry plan, Western said the policy on procurement of vessels, managing port facilities and the loss of multi-ticketing would result in fares rising.
Western said that despite the flagship Road Equivalent Tariff (RET) scheme, the ferry user would soon be paying more.
Western operates the only car ferry between Gourock and Dunoon, after CalMac decided last year that the publicly-owned company should only offer a passenger service on the route, given the presence of an unsubsidised rival.
The profitable Western is known to be ambitious to run more commercial car ferry services to the likes of Arran. Its managing director, Gordon Ross, has long argued that public subsidy should only be given to routes that are not commercially viable – to the likes of Colonsay, Tiree and Coll.
In its submission, Western argues the taxpayer and passengers would be better served by the CalMac network being broken up to allow competition.
The firm states: "This consultation paper seems to indicate that the Scottish Government prefers to see the continuance and market domination by the state-owned company irrespective of the public cost or the service to the islands."
The RET pilot delivered 50% savings in fares to the Western Isles and to Coll and Tiree. However, Western is convinced its extension to other routes to the Hebrides and on the Clyde will not produce the same results. This is because of a policy of building new high-spec vessels for CalMac and ministers' goal of trying to make port facilities self-supporting.
Western believes the latter can only be achieved either through increased subsidy or higher harbour dues – which only subsidised operators will be able to afford.
The roll-out of RET will also mean the loss of multi-journey tickets, which Western says will add to the administrative burden on ticketing staff. It says the operator will lose the cash-flow advantage of pre-paid tickets, which will also in time push up the cost of the service.
Western's submission goes on: "Unless there are fundamental changes to the way that the ferry services are tendered, delivered, operated and managed, the proposals contained within the Consultation Paper will significantly increase the cost of providing these services. Given the current pressure on public finances and the proposal to link fare increases to the future cost of travel, it looks as if the increased burden will squarely fall on those who depend on subsidised ferry services.
"The 2012 fare increase was 6.5%, as such well above current inflation rates. Given the contents of this Paper and a reluctance to make significant changes to the delivery of ferry services, larger increases can be expected in the future. Therefore any reductions in fare levels associated with a network-wide RET roll-out will quickly disappear through fare increases."
Meanwhile, Western says it is hard to reconcile the draft plan's environmental aim of reducing ferry emissions – while rolling out RET, which would promote greater car usage – and increasing the frequency of sailings.
It also observes: "The Scottish Government has ruled out any reductions to service speeds, perhaps one of the most effective methods to cut emissions."
Transport Scotland said: "We will take into account all views as part of this consultation. As a Government we are absolutely determined and committed over the next decade to delivering improved ferry services, and the draft Ferries Plan focuses on the things that we know matter most to our communities."