The annual cost of repairing CalMac's fleet of ferries has tripled in a decade, reaching more than £28 million last year.
A Freedom of Information request by the Scottish Conservatives showed the extent of rising maintenance costs as the fleet grows older.
In 2011, total repair costs stood at £9.5 million, but this rose to £28.6 million in 2021.
Total spending on repairs has gone beyond £200 million since 2007.
The ferry network has been stretched as the ageing fleet of vessels is withdrawn for repairs, with island communities warning MSPs last month that the service was in an "all-time critical situation".
CalMac's oldest large ferry, MV Isle of Arran, is 39 years old. More than a third of the fleet have exceeded their 30-year design life.
The two new vessels being built at Ferguson Marine in Port Glasgow are several years late and more than double their original budget.
Conservative MSP Graham Simpson said: "The age and decline of Scotland's ferry fleet is taking an ever heavier toll on island communities and the public purse.
"More than a third of CalMac's ships are working beyond their design life, and the operator's head engineer has admitted that breakdowns will become more frequent as time goes on.
"It is no wonder that the cost of repairs has soared.
"The SNP have utterly failed to deliver their promised ferry replacement programme, which has forced them to fork out a fortune of public money on ships which should rightly have been retired years ago."
He continued: "Meanwhile, two unfinished vessels in nationalised Ferguson shipyard are several years late and still months away from completion, having racked up costs of more than £250million so far.
"The SNP is letting down Scottish taxpayers and abandoning island residents who rely on these lifeline routes.
"They must urgently deliver the new ferries we desperately need or the breakdowns and delays will only get worse."