The Polar Manager lets you keep examine and edit boat performance data stored in "Polar Files".

Polar Manager

Polar Files

Polar files describe the expected speed of a given boat for various values of wind heading and speed.  The data in a polar file is a collection of triples (ws, wa, bs) where ws is a true windspeed, wa is a true wind angle, and bs is the expected boatspeed when sailed correctly at this windspeed and wind angle. 

BLUEWATER uses this data to interpolate (by cubic splines) the general function bs(ws,wa).  This function is required by the routines which compute performance and routing.  Each route must be assigned a boat type for which a polar file exists before any performance can be computed.  The assigned boat type  can be changed using the “route options” window. (Right-click on a route in the Route Manager or on the chart.)  It is convenient to use boat type names such as “J120” or “Farr40” that correspond to actual designs, but it is not necessary. 

Polar data is called that because it is typically presented as a series of curves of constant windspeed drawn on a polar chart. BLUEWATER RACING” allows a polar curve for zero windspeed giving non-zero boatspeed.  This would, for example, describe a cruising yacht able to use its motor.  You can build polar files for one boat in different configurations (cruising, racing, high seas, flat water, etc), but each route can have only one polar file at a time.

Polar data is stored in one file for each boat type. BLUEWATER RACING can read and write three formats:

BWR will also load data from any file with any extension, and will assume the format is “.plr”.

Polar data should be stored in a file called “<boat type>.<fmt>”.  Thus, the polar data for a J120 would be stored in “J120.plr”, and the Expedition format data for “mytype” would be stored in “mytype.pol”.  Names are case sensitive.

Whenever a performance calculation occurs, the program attempts to load any required polar files by searching through the default polar directories.  The list of polar directories can be modified from Tools→Preferences→Directories. The “Polars” entry should contain a list of folders to search whenever attempting to load a polar automatically.  Folder names should be separated by whitespace.  If a folder name contains whitespace, it should be enclosed in quotes.

If you want to load a polar file that is not in one of these default directories, specify  its full location and file name in the route options.

EG: 

1)    Boat Type(Polar) = “J120”.   BWR will look for a file named “J120.plr” (then J120.pol, J120.sol, J120.csv, J120.txt) in the default directories in order they are listed in the polar directory entry.

2)    Boat Type (Polar) = “J120.sol”.   BWR will look for J120.sol in the default directories.

3)    Boat Type (Polar) = “C:\Users\Jeff\BWR\polars\J120.pol”.   BWR will look for exactly that file.

Polar data for a few boat types is included with the program.  You can get polar data from boat manufacturers or US Sailing.


Upwind and Downwind VMG Targets

Upwind and downwind targets specify what true wind angle the boat should be sailed at to achieve maximum VMG -- velocity made good in the upwind or downwind direction.  Helmsman and trimmers attempt to sail this true wind angle. To make performance predictions, the program needs to know these targets, since it assumes the boat is being sailed according to them.

Expedition format polar files always explicitly encode the target values as part of the specification of the polar curves.  BWR plr files may or may not contain explicit VMG target information.   To include explicit VMG information, a curve is added labeled “upwind” or “downwind” (rather than being labeled by a windspeed number.)   The entries on the line labeled “upwind” consist of windspeed/true wind angle pairs, where the TWA is the target to be sailed.

For .plr files without explicit upwind or downwind curves, and for Sail Online files, which don’t include target information, the program calculates the VMG targets from the polar curves.

The target lines are displayed in the polar manager as magenta lines.  If explicit in the polar file, they are drawn solid and labeled with lowercase “upwind/downwind.”  If calculated by BWR, they are drawn dashed and labeled with uppercase “UPWIND/DOWNWIND.”


The Polar Manager

You can view and edit polar files with the Polar manager.  It lists all polars used by any routes in the races that have been loaded during the current session.  Additional polar files can be opened and added to the list. 

The polar can be edited visually by selected Edit mode in the viewing window.  Then click on a control point and move it to adjust the curve.  Additional control points can be added by clicking in the middle of a curve.

The polar values can be edited in the spreadsheet.  Changes to the spreadsheet are not applied to the edited polar until Apply Changes is clicked.  To add a new curve, choose the new windspeed (or “upwind”/”downwind”) and click Add Windspeed.  At least three control points are required for a new windspeed.

To delete a curve, right-click on it in the treeview window.

Editing changes can be undone/redone through the tools dropdown menu, or with keyboard shortcuts: ctrl-z, ctrl-y for Windows and Command-z, Command-y for Windows.


Polar file format

The .plr and .pol formats are essentially the same, except that .plr allows curves labeled “upwind” and “downwind.”  A polar file is a sequence of lines.  Each curve is described on one line of the text file by a windspeed, followed by a sequence of pairs of True Wind Angle and boatspeed.   (TWA in degrees, BSP in knots)

   eg:

     10 30 0 45 6 90 8.1 160  7 180 5

   15 30 0 40 8 90 12  150 10 165 9 170 5

This gives two curves, one for windspeed 10, one for windspeed 15.  Different curves may have different TWA points, and different numbers of points.  The line for  windspeed 10 specifies a boatspeed of zero knots at a true wind angle of 30 degrees, a boatspeed of six knots at TWA 45, 8.1 knots at 90, seven knots at 160 degrees, and five knots at 180 degrees.

There can be a zero windspeed curve with non-zero boatspeed, i.e., “when the wind is gone, the motor's on.”

Rules for the data in polar files:

1)    One windspeed curve per line.

2)    There must be a least 3 points per curve.

3)    There must be at least one non-zero windspeed curve.

4)    The minimum TWA is zero, and the maximum is 180.

If these rules are broken, the behavior of the program is undetermined.


Building Polar Files from Actual Data

The Polar Manager can construct a polar file from actual measured wind speed, wind angle, and boat speed values. Simply use the "Processed Log File" feature of the Instrument Manager to gather the data into some log file, and then select Build→From Bluewater Logfile. to build the polar. Then choose the processed log file to use, and the polar will be constructed with the same root name as the log file and extension .plr. E.g., instrument.log becomes instrument.plr

The logfile can have been generated over many sessions on the water, in different combinations of wind and angle, and it may have other variables stored in it besides tws, twa, bsp. The program will extract the data it needs. Note: the Instrument Manager opens the processed log file in "append" mode, adding new data to the end of the file if it already exists. If the old data is not desired, then a new file name must be specified (or the old file deleted).

Use Build→From X-Y-Z Data File to construct a polar file from data collected by some other means than BLUEWATER processed logging. You will be asked to select an input file. The data must be stored in this file as triples tws twa bsp, where tws is true wind speed, twa is true wind angle, and bsp is boat speed. The values must be separated by spaces, with one triple per line. Eg.,

10.5 163 7.4
10.2 160 7.2
...


Comparing Polar Curves

The wind curves from a second polar can be overlaid on the diagram of the polar that is being edited, so that the two curves can be compared and possibly the edited curve adjusted. This may be useful in the case that a polar built from data is to be used to modify a theoretical polar. Right click on a polar or polar curve in the explorer window, and select Overlay. The curve(s) will be drawn in black over the diagram of the editing polar. To remove the overlay, right click on the overlaid polar or curve and select Clear Overlay.