CalMac's booking system will be offline for three days later this week for scheduled maintenance.
Bookings, amendments and cancellations will be unavailable from 4am on Saturday May 13 until 5am on Tuesday May 16.
A CalMac spokesperson said: "Please be assured that during this time, our services will be unaffected.
"Travel on our Turn up and Go routes will still be available. Customers should proceed to their port as normal.
"For bookable routes, existing bookings will continue to be honoured. Customers should proceed to their port as normal.
"For new bookings on bookable routes during this period, these will be operated on a turn up and go basis and any available capacity will be advised in person at the port prior to sailing.
"Also, our Urgent Medical Protocol will still apply during the downtime. Any customers requiring urgent travel at the last minute can contact their local port staff who can help them to travel.
"If customers want to make an advance booking for travel on or after Tuesday, May 16, we are asking them to please wait for the introduction of the new booking system on May 16."
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