We use similar terminology to any other public transport network. If you arrive before the scheduled departure time for a train or a bus and have to wait to be boarded before the scheduled departure, your journey would not be described as delayed.
If we are running to timetable (or as close as reasonably possible) and clearing the lanes of every vehicle that arrived in reasonable time to be loaded for that departure, then there is no delay. If there are so many vehicles in front of you that you would not catch the next available ferry, or if the ferry is running significantly out of cadence with the schedule, then this would be considered to be a delay.
https://www.tamarcrossings.org.uk/support/faqs/delays-why-do-you-say-that-there-are-no-delays-when-im-sitting-in-the-lanes-waiting-for-a-ferry-and-there-are-none-on-the-slipway/Copy Link