OpenCPN

Help Information

This Information is available from within the plugin from the Help Menu by selecting Information

Introduction

The Weather Routing Plugin is designed to compute iteratively positions the boat could possibly make at a certain time. By merging the results of many calculations, it is possible to form a map determining routes to any given location within the map.

Quick Start

First, load the grib file used for routing using the grib plugin. Next, open the Weather Routing plugin from the main toolbar and right click the map and Select "Weather Route Position" at the starting location. Repeat this step for the destination. Now, in the Weather Routing window from the Configuration menu (next to File) Select "New". From here you must configure your vessel correctly in the boat dialog; add a polar to specify how the boat sails. When ready, select "Compute" from the Configuration menu to compute the weather route.

Background

Integration with the grib plugin allows for knowledge of weather conditions. The climatology plugin can also provide a source of data for longer voyages, but be warned that using the climatology data, especially in variable wind areas is unlikely to give realistic results. Using climatology for currents is more useful and can be used with grib wind data when grib current data is not available.

For example, in the case where data is valid from both sources, grib will always be choosen. If current data is available from climatology, and only wind from grib, then the grib wind is used with the climatology current.

The grib time selected on the timeline at the time the computation is started can be syncronized. From there, the grib timeline data is accessed as the computation proceeds. Once a computation is completed, the course and position of the boat as it sails along the computed route can be viewed during grib playback.

Wind data is required; if no Current or Swell data is available, they are assumed to be zero.

Configuration

Basic Tab

Start - Date & Time

  • Make new postions by Right-click on the Chart and select Weather Route Position

  • Position: Select Start Weather Route Position from drop down menu

  • Date: Select Date & Time (Must be within grib time frame)

    • Grib Time: Sets date & time to Grib_pi active file date & time. Adds checkmark.

    • Current Time: Sets date & time to current date and time. Removes checkmark.

End

  • Position: Select End Weather Route Postion from drop down menu

Time Step

  • Time to sail before considering a course or sail change.

  • This is the difference in time between the isochrons on the map.

  • Small time-steps are needed to navigate through narrow channels and give a more accurate result.

  • Generally the route’s finish becomes earlier with smaller time steps because a more optimal route is found, however calculation will take longer (generally four times longer for half the time step).

Boat

Path to Boat.xml

  • Click on the "…​" to set the path or change the Boat.xml file.

  • Windows Example:

    • C:\ProgramData\opencpn\plugins\weather_routing\boats\NorthStar.XML

Edit Boat.xml

  • Edit Boat.xml opens up a menu intense portion of the Routing Configuration:

  • Plot Tab specifies the parameters for the plot displayed.

    • Polar Typical polar diagram showing boat speeds at a given wind speed.

    • Speed Plot boat speed across all wind speeds at a given wind angle.

    • The tracking displays give data based on the mouse position over the plot.

  • Crossover Tab Shows the relationship of the polars and which one is used for each condition.

  • Stats Shows optimal Target Boat Speeds and Angles at downwind/upwind port/starboard tacks at various wind speeds.

  • Bottom Drop Down Menus

    • Polar diagram and Speed orthogonal diagram

    • True Wind Direction / True Wind Speed Selection of combinations of Wind direction & speed to use.

  • Add Polar Files from the Boat.xml file.

  • Remove Polar Files from the Boat.xml file.

  • Open Boat Open an existing boat file.

  • Save Boat Save current boat file.

  • Save As Boat Save current boat file to a new name.

  • Multiple polar files can be added to the Boat.xml for:

    • See the example polar files.

    • Wind Ranges (light, medium, heavy) and corresponding Sail Sets.

    • Sea State (flat, chop, rough)

    • Bottom Condition

    • Power Polar for light winds

    • The best polar file will be automatically selected for the routing when the route is being "Computed".

  • Edit Polar File (.csv .txt .pol) opens up another window which permits editing the polar file.

    • Grid Tab Edit values in individual cells. Note use of:

      • blank = Interpolate from nearby values, if at least one set of values of tws/twd are entered in the column/row.

      • 0 = Not recognized by the program, will remove these it edited. Sometimes a polar will contain 0’s. They should be removed.

      • 0.0 = Specifies invalid (cannot be used). Boat won’t move and can’t go there.

      • Cancel and Save

    • Dimensions Tab Use to add or remove wind angle/speed columns/rows

      • Set the values in the the first column (twa) and first row (tws).

      • Cancel and Save

    • Generate Tab Generate a boat polar from Boat Characteristics (VPP) or from actual Measurements of Wind Dir/Speed.

      • Cancel and Save

      • This feature is not fully implemented.

Constraints

Max Diverted Course

  • Maximum course error to continue toward destination. Not all possible courses will be considered and therefore the most optimal route may not be found.

  • This usually (but not in all cases) is obvious when the optimal route is sometimes near the edge of the graph. Using a reasonable value can greatly speeds the rate of computation.

Max True Wind

  • Knots. Do not navigate in areas

Advanced Tab