Optimal Tacks in the SailTimer app with the Wind Instrument

We provide a Wind Gauge app for Android, and the SailTimer API™ to provide NMEA 0183 data for viewing on other marine electronics.  But the free SailTimer™ app gives better navigation information than even the most expensive GPS chartplotters. When using the Wind Instrument, as the wind changes, the SailTimer app updates your tacking results automatically.


Here is a list of some of the unique features that you can get in the SailTimer tacking app, when using the SailTimer Wind Instrument.


Although the wind speed and direction from the Wind Instrument can be displayed in other software, the SailTimer app is unique in using a speedometer to show the wind speed. Marine anemometers have traditionally just used numbers for the wind speed, but we think this is more interesting and easier to see quickly.

Note also the orange arrow on the dial around the outside of the Wind Speedometer, showing the wind direction.  If you make the speedometer into a small icon to see more of the chart, the wind is then displayed as an arrow around the boat.

You can also convert between True and Apparent wind direction and wind speed here, using the button in the upper right corner of the screen.

When the Wind Speedometer is open, you can click on the Graph button to get the above display.  This is an interesting way to review your sailing for the day, by comparing your boat speed with the wind speed.  Both Apparent and True Wind Speed are shown on the graph.

If you have ever noticed how the wind seems to calm as soon as you head downwind (even though your boat may still be going fast), this is easiy to see on the graph.  In that case, the SailTimer app converts the Apparent Wind Speed to True (the same as the wind speed in the weather forecast, without accounting for the movement of the boat).  So as the Apparent Wind Speed drops when you head with the wind, the blue line on the graph drops to the same level as the boat speed.  But the wind hasn’t actually slowed down, so True Wind Speed remains at the same level.

You can easily share this record of your day’s sailing experiences from the app, by clicking Email in the upper right.  You can even email it to yourself.

Notice in the background that your boat location is shown with the GPS track. You can save this by taking a screenshot (holding down the power button and Home button at the same time, until you hear the camera shutter sound).  The screenshot is saved into the Photos app, and can be emailed from there.  Or, if you want only the graph with no background image, use the Email button in the upper right.

But the SailTimer app doesn’t just show your wind speed and direction, as traditional marine anemometers have done.  It continually updates your tacking results as the wind changes.  So as data arrives through the air from the SailTimer Wind Vane, the optimal tacks and Tacking Time to Destination (TTD ®) are updated automatically.

Polar plots are an advanced feature that we are now making easily accessible to all sailors. As you can see in the table above, the polar data stores your boat speed for different wind angles and wind speeds.  When the SailTimer app knows the boat speeds for your unique vessel, it can provide better results for your optimal tacks and Tacking Time to Destination (TTD ®).

Traditionally, it was difficult to get polar plots.  You may be able to get them from some boat manufacturers, or some racing organizations have sold a page with a generic polar (but see the problems with these approaches here).  Rather than generic estimates, polar learning in the SailTimer app collects actual data on your individual sailboat.

You can see the data being saved on the table above, while you are underway. You can turn on/off the Polar Learning as needed, so that once you get good data saved, you can keep using it without affecting it later.

The SailTimer app also makes it easy to save polar plots for different conditions, different boats or different sail combinations.  For more details on how the optimal tacks are calculated using your polar data and tacking distances, see this case study.

Note the grey wind arrow beside the boat, showing the wind direction coming through the air from the SailTimer Wind Instrument™.

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