Tidal Window
A Tidal Window is the span of time, usually centred on high water, during which the height of tide provides enough water for a deep-draught ship to enter, leave or transit a depth-restricted port or channel with the required under-keel clearance. Outside the window there is not enough water and the ship must wait.
Tidal windows are calculated from the tide predictions, the ship draft and the minimum UKC, and they shape the timing of port calls for large ships: arrival, pilot boarding, berthing and sailing are all planned to fall within the window. Missing a tidal window can mean waiting for the next tide, sometimes many hours, with cost and schedule impact.
For deep-draught ships in tidal ports, the tidal window dictates the entire timing of the call — when the ship can arrive, berth and sail. Missing it means waiting hours for the next tide, so building the whole port call around the window is essential to schedule and cost control.
What determines the length of a tidal window?
The ship draft and required under-keel clearance against the tide curve: the deeper the ship, the shorter the period around high water when there is enough depth. A shallower ship has a wider window.