A possible feasible route with a preferred route width is sought that only crosses kilometer points through safe time intervals. Together with the first and last moments that the route can start and end, this forms the tidal window.
Advice route calculation
After the safe time intervals are determined and corrected for the cross current the algorithm tries to find a safe route with a desired minimum route width. The algorithm starts at the first available safe time interval on the most restrictive kilometer position in the channel and then tries to reach the berth and start of the channel from there. The algorithm starts with a minimal time window width of 0.5 hours and on failure tightens the desired width. This minimal width is modeled by narrowing each safe time interval with the route width. When a route can be found through the "narrowed" time location table, then we know we have found the advice route with the minimum route width.
The illustration below shows the idea of the algorithm by starting at the most restrictive kilometer position and then traversing the safe time intervals until both berth and start of the channel can be reached in one straight line.
First and last routes define the tidal window
A tidal window is more then an advice route. It should also give the very first moment before the advice route the voyage can start and the very last moment. Together these moments form the opening and closing of the tidal window around the advice route. This calculation is done by taking the original safe time location (the diagram before the narrowing process mentioned above) and then remove all the safe time segments that are not crossed by the advice route. If we now find the very first and very last route in this new diagram, we have the desired tidal window. The tidal window is shown by the aqua and red colored lines in the time location diagram. The advice route is drawn in green.
