Before trusting a wind reading, it is worth knowing where it comes from. WindTrackr connects real weather stations installed at the beach. This guide explains how sensors work, what they actually measure, and why that matters when deciding whether to head out on the water.
1. Types of anemometer
An anemometer is the sensor that measures wind speed. There are a few different types, each with their own strengths:
- Cup anemometer (mechanical): The most common type. Three or four cups spin with the wind, and the rotation speed is converted into knots. Very reliable, though slightly slow to react to sharp gusts due to mechanical inertia.
- Propeller type: Similar to aviation design. Good accuracy when bearings are in good condition.
- Ultrasonic (no moving parts): Measures the time it takes sound pulses to travel between two points. No friction, responds almost instantly to each gust. The most precise type, though also the most expensive and delicate to maintain.
In practice, most coastal stations use cup anemometers. Ultrasonic sensors are more common in professional installations or spots where gust precision is critical.
2. How wind direction is measured
The wind vane tells you where the wind is coming from. For the reading to be accurate, it must be aligned with true geographic north, not magnetic north.
When wind is very light (below 3 knots), the vane can oscillate erratically. Modern sensors filter out those oscillations to avoid showing confusing data.
Current encoders measure direction to a 1-degree resolution, which is more than enough to tell whether the wind is offshore, onshore, or sideshore at your spot.
3. Where sensors are installed
A sensor in the wrong spot gives wrong data, no matter how good the hardware is. Location matters as much as the device itself.
- Standard height: The World Meteorological Organization recommends installing sensors 10 meters above open ground. This makes readings comparable across different stations.
- No nearby obstacles: Buildings, trees, or cliffs create turbulence that distorts readings. The usual rule is to place the sensor at a minimum distance of 10 times the height of the nearest obstacle.
At WindTrackr, we take each station's location into account. A sensor directly exposed to the sea provides much more useful sailing data than one installed behind a building.
At sailing clubs, masts are typically designed to clear surrounding structures and capture the real wind coming in off the water.
4. Calibration and maintenance
A mechanical sensor in a coastal environment needs regular checks: bearings corrode with salt and can eventually seize up, causing the sensor to report lower speeds than the real wind.
Ultrasonic sensors have no moving parts, but salt and dirt build up on the transducers. They need protective grilles and regular cleaning to stay accurate.
Official weather stations are calibrated at least every six months, which ensures a 25-knot reading actually represents that speed.
5. How to read sensor data
Knowing the sensor type helps you interpret the data more accurately:
- Cup anemometer: Recorded gusts are often slightly lower than the real peak, because mechanical inertia does not react instantly. If the sensor shows a 28-knot gust, the actual peak may have been a bit higher.
- Ultrasonic sensor: What you see is essentially what happened in that moment. A 30-knot reading is the real captured peak.
- Sensor height: A sensor installed 3 meters off the ground will measure lower wind speeds than one at 10 meters, because wind is always slightly slower close to the surface. Factor in the mast height if it is very low.
WindTrackr displays data exactly as received from the sensor. Understanding its limitations helps you read that data with more confidence.