Our cargo division runs short-sea freight in the central Aegean, and every winter the same argument surfaces in the scheduling meeting: how much slack should the timetable carry? It is a question with a real cost attached in both directions, and it is worth setting out the arithmetic rather than relying on the feel of it.
The route in question
The leg that generates the argument is Lavrio to Syros. Under normal conditions it is a four hour forty minute passage for our Ro-Ro tonnage, and the published schedule is built on that figure. It is a short leg by any standard, which is precisely why the slack question bites — a delay that would disappear inside a two-day passage has nowhere to hide inside one of under five hours.
What actually causes the delay
Not the weather itself, most of the time. Our operating threshold is Beaufort 7; above that the sailing is cancelled rather than delayed, and a cancellation is a clean outcome that everyone can plan around. The expensive case is Beaufort 5 to 6, where the vessel sails but the passage stretches, and the berth window at the far end has already been allocated to someone else.
A missed berth window in Syros in February does not cost you the difference in arrival time. It costs you the wait for the next window, which can be several hours, and it cascades into the return leg.
Anemos II and the lane-metre problem
Our vessel on this route, Anemos II, carries 412 lane-metres. That number sets the whole economics. Filling it requires committing to bookings well before the weather picture is clear, and a Ro-Ro sailing at sixty percent of lane capacity loses money whether it arrives on time or not.
The tension
Building slack into the schedule protects the berth window but reduces the number of sailings you can offer, which reduces the lane-metres you can sell. Building a tight schedule sells more capacity and then fails to deliver it in the months when the weather is worst — which are also the months when the freight rate is highest.
Where we landed
We now run two published timetables, a summer one and a winter one, with the winter version carrying an additional ninety minutes on the Lavrio–Syros rotation. Customers dislike the winter timetable and book it anyway, because the alternative is a summer timetable that is fiction from November onwards.
Telling customers the truth
The thing that improved satisfaction most was not the extra slack. It was publishing the cancellation threshold. Once shippers knew that Beaufort 7 meant no sailing, they stopped calling to ask and started planning around it. Predictable bad news is worth a great deal more than optimistic scheduling.