How accurate is your wind data when heeling over 15-20 degrees?

The Accuracy Issue

The SailTimer apps for receiving Bluetooth wind data have had many updates over the past few months on Android and iOS, as we refine and improve the raw data to give you the most accurate True Wind Speed and True Wind Direction.  That is a good reminder of various ways that you can ensure you are getting the most accurate wind and navigation possible. Accuracy is a big issue. If your data doesn't let you choose the best route, as we know in sailing, the geometry of the tacks multiplies how late you'll be...
Have you been measuring it wrong? Ultrasonic, traditional wind cup and propeller anemometers all lose accuracy when heeled over. This YouTube video about the original design of the SailTimer Wind Instrument shows (at 45-second mark) how standard wind cups slow down as the tilt increases.

Which wind sensor is most accurate? The SailTimer wind blades are designed for sailboats (details here). If you want accurate data, this is the only masthead anemometer that remains equally accurate regardless of tilt.

How accurate is your wind direction or wind angle? SailTimer is one of the (if not the) only masthead anemometers with a built-in digital compass. It can give you Apparent and True Wind Direction when you are swinging sideways at anchor, or when parked with no GPS movement. No calibration to the bow of the boat when installing; it knows which way it is pointing all the time. Even if you wave it around in mid-air, as in this video (at 33 second mark) about the original design.

Is your boat's compass updated for NOAA's World Magnetic Map (WMM)? If you are using an old-style anemometer that measures wind angle, and then converts that to wind direction based on a compass in the boat (e.g. for the auto-pilot), how accurate is that compass for True North? Maybe good enough to keep the autopilot on a straight line, but accurate enough for converting from Wind Angle to Wind Direction and from Apparent Wind to True Wind? Has the compass been updated given the rapid movement of the magnetic north pole in recent years? The SailTimer Wind Instrument has a state-of-the-art digital compass, and gets over-the-air updates for calculating the most accurate magnetic declination (details here). Measuring wind angle with a potentiometer, then converting to wind direction using an out-dated compass in your NMEA wiring, may not be giving you accurate wind direction.

Is there a dead zone in your anemometer's rotation? Standard anemometers with a potentiometer to measure wind angle have a dead zone of 6 or 7 degrees at the end of the rotation, where the voltage resistance is reset. That is one of the advantages of using a digital compass in the SailTimer Wind Instrument. Our full list of features and innovations is here.

Do you have an accurate way to determine your optimal tacking route? When choosing tack headings, being off by even a small amount can make a big difference in your arrival time. The SailTimer app can learn your boat's polar plot (performance profile on all points of sail), and then use this to calculate your route with the fastest Tacking Time to Destination (TTD ®). The SailTimer app is the only product that uses your tacking distances when calculating your optimal tacks and TTD. A sign of the times: our free app has better functions for sailboat navigation than any GPS chartplotter or MFD at any price. See how easy it is to use the app in this 1-minute video.

Which wind forecast is most accurate? Marine weather forecasts are hardly precise, as we all know. Actual wind measurements are not even used to create the forecast; it is based on low-resolution satellite imaging. Robert Sherer, a contributing editor at Waterway Guide, did a good series of tests while travelling the ICW on the US east coast. He found a lot of variability when comparing different apps and the NOAA Coastal Forecast. But at SailTimer, we don't predict wind; we are like the un-forecast. Our crowdsourced wind maps are based on actual wind measurements. Standard GRIB wind maps in apps and forecasts often have resolution from satellite imaging of 1 degree (60 nautical mile cells), 0.5 degree (30 nautical miles) or 0.25 degrees (15 nautical miles). But crowdsourced wind maps have resolution of 10 meters, for accuracy that is orders of magnitude better. We can archive that data, so we know how the wind flows through a channel or around a headland. We had end-of-year announcements in 2015 and 2019 about the ongoing development, and will be releasing a major new new interface and cloud platform for crowdsourced wind maps in 2022. Stay tuned; this is going to be a transformative change for marine weather and navigation.


Most Advanced Features, Lowest Price

SailTimer made the first-ever masthead wind sensor that could transmit to smartphones. Our newest model is the SailTimer Wind Instrument RB™ with Removable Battery in the nose cone (where it serves as a counterbalance). The pointer is carbon fiber to reduce weight. Wireless and solar-powered. Works with lots of apps for racing, chartplotter and wind gauge.

Black Friday bonus: Until the end of this month, orders will ship with a free L-Bracket and Track Slider, for raising the Wind Instrument on a halyard. No need to lower or climb the mast. Plus a stainless steel quick-release wing nut. A $40 value from our Accessories page.

Order here. Just $470 -- or $26.99 per month. Supply chains are sketchy these days so order now while we have it in stock. Next-day shipping.
Marine Equipment Trade Show (METS) 2021

If you happen to be in Amsterdam at the massive METS boat show this week, you can find the SailTimer Wind Instrument on display in booth 03.319 hosted by Marine Components International, distributor for SailTimer in Britain and Europe.


Copyright © 2021 SailTimer Inc. All rights reserved. SailTimer, Air Link, SailTimer Wind Instrument, Wind Instrument RB, Audio Navigation, Speedy Trailer Lights, TTD® and the above tacking logo are trademarks of SailTimer Inc.

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