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Why vertical wind sensors make sense for performance sailing

Measuring the wind accurately is a difficult nut to crack. On land, it’s relatively simple, but afloat, the sensor is mounted on a moving boat at the rolling and pitching masthead. Add in the effects of the boat’s motion and the effects of the sails, and getting accurate data is a real challenge.

The problem

Looking down from above at a boat sailing close-hauled, the wind will bend around the boat and its sails, accelerating through the slot between mainsail and jib, and slowing where it encounters the resistance of the hull and rig. Like water flowing over a rock in a stream, the flow of air will bend around the obstruction. A wind sensor located in this disturbed flow is only going to be able to measure what it experiences – which isn’t a true representation of the wind conditions.

In addition to the way the wind behaves around the boat, think of all the obstructions to air flow that are present: A full mainsail – especially the new generation of square-topped sails - is a huge aerofoil that accelerates the wind and leaves behind disturbed air. Masthead Spinnakers, especially on heavy displacement boats have a similarly large effect.

Masthead obstructions like navigation lights, antennas and radar reflectors all add wind shadows and effects at various angles of sailing. Sometimes a standard wind sensor will never be able to collect truly accurate data - and no amount of calibration can fully cancel out the effects of sail plan disturbance.

Upwash

Sailing dead downwind, the wind accelerates up the mainsail and tumbles over the masthead. Most wind sensors will over-read downwind for this reason.

Upwind, the effect of the sail plan and upwash causes the apparent wind angle that is measured to be further aft than the actual wind stream.

This effect is countered by another phenomenon – that of mast twist. The loads on the mast (in particular the mainsail and, where present, running backstays) cause it to twist and project the sensor arm closer to the wind (and thus the angle will be measured as relatively closer to the wind).

The amounts that each of these affect the wind angle will change with wind speed (for example, there will be less mast twist in less wind, and less upwash.)

The solution

The solution is a Vertical wind sensor. The carbon wand elevates the sensor head into clean air, above the masthead – clear of any effects caused by masthead lights and fittings, and clear of sail-plan disturbance.

B&G’s new WS700 series vertical wind sensors take everything we learned in the development of our new sensor head – subjected to 200,000 hours wind tunnel and field testing – and places it on a high-modulus carbon spar for the ultimate in performance wind measurement.

Coupled with the extra calibration options available on H5000 systems, that means accurate wind data, essential for accurate tactical calls on the racecourse and precise, dependable steering under autopilot – backed by the reliability of B&G’s construction and 60 years of race-winning heritage.

Find out more about the WS700

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