Some 5,653 ferry runs were cancelled across the Cal Mac network last year.
Bad weather caused the most problems, preventing 3,811 sailings.
Some 1,069 trips were cancelled due to breakdowns and technical faults amongst the aging fleet -
The figures were obtained by a Freedom of Information request from the Scottish Greens.
The party’s transport spokesman, MSP John Finnie, expressed concerns at the”greatly increased” number of breakdowns.
He said: “Behind these cancellations are people unable to attend hospital appointments on the mainland, missed job interviews, small businesses unable to send and receive goods, and a loss of important tourism revenue.
"We know that the bulk of the fleet needs renewed. The average age of the CalMac fleet is 23 years and the Scottish Government's own ferry plan for 2013-
"This hasn't happened and we're left with the situation where we have an ageing fleet which requires longer periods of maintenance and repair."
Robert Morrison, operations director at Cal Mac, said the shipping firm had a 99.35% reliability rate with 1,069 technical issue cancellations out of 169,000 sailings last year.
Over £21 million is being spent on overhauling the fleet this winter including a record £9 million on vessel upgrades.
"More than 90 major projects will be carried including new engines, replacement pitch control systems, new bow thrusters, replacement ramps and new generators on various vessels,” he highlighted.
"While reliability currently stands at around 99.35%, we look forward to working with all interested parties to continue to deliver improvements, building on the substantial investment in routes, services, vessels, harbours and fares which have been made in these services in recent years and which have led to significant improvements in connectivity, capacity, affordability and passenger numbers."
MV Isle of Lewis suffered a number of technical issues ast year
Over 1000 Cal Mac sailings cancelled last year by technical faults
19 February 2020