Calculate route

Van veilige tijdsintervallen naar een tijpoort advies

After the safe time intervals are determined the next objective is to find a route with a desired width starting at the start of the channel (40 to 60 kilometers at sea) via the harbor entrance where we can expect cross current and to the destination (given berth). This is done by traversing the safe time intervals starting at the most critical kilometer position (least width) and calculating the times the ship could be at other locations while taking into account the ship speed and the expected current speed and direction.

Preferred tidal window width

The tidal window should be as wide as possible (to give extra room for navigation and speed differences for pilots), but also the ship has an objective to enter the harbor as soon as possible. We try this by starting to look for a route with a 2 hours preferred width, but each time we cannot find a route we half this preferred width down to a minimum of 15 minutes (the granularity of the time location diagram).

Pseudo code

desired route width = 2 hours
while no route found and desired route width >= minimal route width (15 minutes)
  find most critical kilometer point and first safe time
  
  //first try to reach berth starting at this point:
  while berth not reached
    if time is not safe for at least desired route width
      get next safe time for this kilometer point
    find next time location point with the given speed
  
  //next try to reach start of the channel:
  while start channel is not reached
    if time is not safe for at least desired route width
      get next safe time for this kilometer point
    find previous time location point with the given speed
  
  if route is found
    calculate bottom touch probability and save route
  else
    half desired route width

Algorithm visualization

The visualization shows the (orange) traversal from the most critical (narrow) safe time interval up to the start of the channel. Each time the next step in the traversal was not feasible, the algorithm shifts to the first available safe time (with the desired width). If a traversal is possible from start channel to berth, without shifts, then this is the tidal window advise.