To calculate a tidal window a probabilistic methodology is used that simulates a set of possible conditions to determine exact times and locations that the probability of touching the bottom is below the safety criterion. Then a route is found through these "safe" moments to determine the tidal window advice.
The first step in the tidal window calculation is the initialization step. In this step all relevant information is collected.
The possible vertical motions are calculated by analyzing probable movement extremes per depth/draft ratio, speed, swell height, wave height and course.
Per kilometer position a root finding algorithm is used to find the times where the safety criterion is exactly met. The intervals between these roots are the safe time intervals. Together they form the safe time location diagram.
The intervals that the cross current at the harbor entrance (0-kilometer position) exceeds the maximum are excluded from the safe time location diagram.
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.
When a route is found, it is analyzed in detail to calculate statistics on the water level, channel depth, UKC, squat, swell height, vertical motion and bottom touch probability per kilometer position. Also the down time, wait time, UKC and bottom touch probability are calculated for the whole route.
The actual chance of touching the channel bottom is compared to the Maximum route bottom touch probability setting. When the actual chance is higher PROTIDE automatically restarts the calculation with the Maximum route bottom touch probability as the maximum chance per segment in the time / location diagram.