The island's ferry committee issued the warning as it urged CalMac for a contingency plan.
Islay and Jura are set to lose MV Finlaggan on June 4 when she goes for a delayed drydock. 'Fin' is due to be replaced by MV Hebridean Isles, but that ferry is still out of service after a fault in February. Islanders fear 'Heb Isles' may not return in time.
That leaves them with just MV Isle of Arran during most of June, plus MV Alfred, hired by the Scottish Government for £1million per month.
But Alfred cannot dock at Kennacraig, said Islay Community Council Ferry Committee (ICCFC), and would have to sail from Campbeltown, adding hours to the journey time.
And then the MV Isle of Arran developed a problem.
In a stark warning on May 16, ICCFC told the ferry operator CalMac: "We know that after several months in dock, the specific problem that is keeping Heb Isles from service has not yet been identified.
"CalMac is unwilling to use extra crew to operate any additional sailings of Isle of Arran or Alfred, and we are aware of no alternative contingency plan to provide Islay with additional capacity if Heb Isles remains out of service after Finlaggan leaves for drydock on June 4.
"It would be a breach of 'lifeline' service obligation to leave Islay with only Isle of Arran in June, with or without an added Alfred trip via Campbeltown. The resultant capacity reduction of more that 50 per cent would cause meltdown for community and business.
"Lack of progress in any of our discussions with CalMac and a continuing lack of contingency plans or even consultation with our community are becoming serious concerns.
"If Heb Isles does not return to service by 4 June, the necessary two vessel service could not be fulfilled by 'Alfred' as one of them. Alfred cannot call Kennacraig - the nearest alternative is Campbeltown and due to the extra transit time this vessel would manage only one crossing each way. The combined capacity of Alfred and Isle of Arran (which is being used just now) would not meet the requirements in June."
Then, on Sunday May 21, the MV Isle of Arran experienced a "steering" problem, suspending sailings that evening from Kennacraig and the next morning from Port Ellen. All booked cars (around 40) were left behind at Kennacraig on Sunday night, ICCFC said.
A CalMac spokeswoman said: “We are sorry that we have not yet been able to confirm a return date for MV Hebridean Isles, this is obviously causing frustration to islanders and visitors. Please be assured that everything is being done to ensure that two vessels will serve Islay when MV Finlaggan leaves for annual maintenance.
“Repairs to MV Hebridean Isles are progressing well this week, work is continuing and she has been out on sea trials. We will contact our stakeholders with a return to service date as soon as possible.”
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