Vessels pile up at anchor while a surge rolls in. Open too few berths and demurrage explodes as ships wait; open too many and the quay burns cash. Clear the queue before the crisis buries you.
A container terminal is a queueing system: vessels arrive, berths (with cranes) serve them. When arrivals exceed berth capacity the anchorage fills and demurrage - the cost of waiting ships - escalates non-linearly.
Each period a surge of vessels meets your open berths and crane rate. Unserved ships wait at anchor and carry into the next period; gate throughput must clear the yard or congestion adds cost.
Open berths early in a surge to keep ρ below 1 - waiting cost climbs far faster than the fixed cost of an extra berth. Match gate throughput to arrivals.
