Wind Readings

The wind is constantly changing in both direction and strength, especially on a relatively small body of water like Candlewood Lake. Since we are never far from shore, the surrounding hills and trees can affect the wind patterns on the water. To minimize these effects, you should take wind readings in the middle of the lake. You should take a series of readings to determine the average wind speed and direction.  The wind may oscillate (swing back and forth within a consistent range) or have a persistent shift (continuously changing in one direction). With an oscillating wind, we need the average wind direction for the course axis. With a persistent shift, we use the most recent wind direction. We also need to know the sustained, or average, wind speed and the speed of the gusts. Wind shifts frequently accompany gusts. The wind speed determines how long the course should be and is used in the PHRF calculation. We need a sustained 5 knots to race. Winds exceeding 17 knots may be too strong for the Flying Scots to race safely. The stewards will go out on the lake as soon as possible to start taking wind readings, before the RC Boat. They will report their readings to the PRO, who should also take their own readings.

Preparation

To take wind readings, you will need four things: a hand-bearing compass, a wind stick, an anemometer, and a Wind Record Form on a clipboard to record your readings. All of these items are inside the black race box stored under the aft port seat in the RC Boat. The wind forms are stored inside the clipboard, along with the scoring sheets. Rubber bands are inside the box to wrap around the bottom of the clipboard to keep the paper from flapping in the breeze. The wind stick is a wooden dowel with a piece of audio cassette tape attached to the top. This allows for accurate, precise measurement of wind direction, even in light air or rain. The audio tape is fragile; if it breaks, it must be replaced. There is an audio cassette tape cartridge inside the black box. To use it, tear off a piece of audio tape about 8 inches long and attach it to the dowel with the electrical tape found inside the black box. We use the anemometer to measure the wind speed. When you turn it on, first make sure that it is set to read in knots. The display will indicate the unit’s setting on the upper right. There is a “UNIT” button that changes to different units. The anemometer has different modes. When you turn it on, it will display the instantaneous wind speed. We want the average speed. The “AVG” button in the bottom-right corner will set this mode. In average mode, “AVG” will display below the wind speed. For more details, see the Anemometer Instruction Manual.

How to take wind readings

You need to take several wind-bearing readings to determine the pattern of the shifts. You only need a couple of wind speed readings, unless there is a gust or a significant change. The PRO can take the readings while the crew records them on the Wind Record Form. To take wind readings, go out to the middle of the lake and make sure the boat is completely stopped, facing into the wind. If the boat is moving, it will throw off your wind readings. To verify that you are not moving, look at the water next to the boat for signs of movement. If you are already anchored, you don’t need to worry about this. Move to the front of the boat and face into the wind, so that nothing in front of you will obstruct the wind.  Hold the wind stick with the audio tape high, at arm’s length, directly in front of you. Hold the hand-bearing compass behind and in line with the wind stick. Do not hold the radio near the compass; it will throw off the compass. Read the compass bearing for 10 to 20 seconds, and record the average direction. To measure the wind speed, hold the anemometer up facing into the wind. Use the wind stick to make sure the anemometer is pointed directly into the wind to get an accurate reading. Hold the anemometer up for 20 to 30 seconds to get a good average reading. If there is a gust, change the anemometer’s mode to MAX. Hold the anemometer up to get the maximum speed of the gust. Make sure to set it back to the AVG setting for the next reading.

Wind Record Form

Record the time, speed, and wind direction on the Wind Record Form. To visually recognize the wind shift pattern, use the grid on the form. For the first reading, enter the bearing in the center column marked 0. For each subsequent reading, enter the bearing in the column indicating the change in bearing from the first reading. For example, if the first reading is 180°, write that in the center column. If the next reading is 170°, write that in the column marked -10. If the third reading is 185°, write that in the column marked +5. After several readings, you can quickly see the pattern of shifts.

For the stewards:

As soon as you leave the dock, go out into the middle of the lake and start taking wind readings. Take wind readings every 5 to 10 minutes. If you see darker water approaching, that indicates a gust, and you should record it. Determine if the wind direction is oscillating or if there is a persistent shift. Report your readings to the PRO when they are ready to copy.  If the wind is oscillating, report the average wind direction. If there is a persistent shift, report the current wind direction and the direction from 15 minutes earlier. Provide both the sustained (average) wind speed and gusts. For example: “The wind is 8 knots with 12 knot gusts, oscillating with an average direction of 215°.” The PRO may ask you to take wind readings at various points around the lake. Continue taking readings periodically throughout the races to look for any significant changes. If there is a change, report it to the PRO.

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