Windspeed With No Moving Parts

Sonic masthead wind gear may make cup and vane anemometers a thing of the past. "Electronics" from our January/February 2009 issue

January 22, 2009

****| |The Maretron WSO 100 delivers wind data without the cups and moving parts of a traditional masthead anemometer. Windspeed and direction are measure by sonic pulses passing between the sensors (explained in the diagram below).| When you have a delicate instrument with moving parts spinning around at the top of your rig, there are bound to be numerous trips aloft to replace bits and pieces of your wind direction/speed sensor in its lifetime. Broken vanes, missing cups, and wands tweaked off centerline are the stuff we’ve long had to deal with to get the wind data we need. But two companies, Maretron and Airmar, have developed wind speed/direction sensors that use no moving parts. Using sonic technology, these units provide accurate information about wind direction and speed, as well as barometric and temperature information. Consider them as masthead weather stations.

Will this technology benefit racing sailors? “Absolutely”, says Maretron’s VP, Larry Anderson. “The information from our WSO 100 sensor feeds information directly to a NMEA 2000 backbone, which also has compass, GPS, and speed information. Those bring the corrections for the true component of the wind that you need and want.” Any system that’s capable of reading NMEA 2000 messaging, he tells us, can use this data.

Such compact systems are commonplace on powerboats and the major concern has always been whether the systems would work on a raceboat.


“This is even better than some mechanical units,” says Anderson. “It’s been designed aerodynamically to work on an angle of up to 30 degrees of heel with no degradation of accuracy whatsoever.”

So how does this sonic technology work? The Maretron sensor consists of three ultrasonic transducers. One by one, the three sensors generate ultrasonic sound pulses, which are received by the unit’s other two sensors.

Courtesy of Maretron| |****|


According to Anderson, wind blowing in the direction of flight of a pulse increases the speed of the pulse by the amount of the windspeed. “Measuring the time of flight in both directions between a pair of transducers allows the speed of sound to be cancelled out of the calculation, making the wind speed computation independent of air temperature and relative humidity.”

Alex Agnew navigated the Swan 40 Chase in the 2006 Newport Bermuda Race using the system. He did the installation himself, although he’d never done that type of installation before. “I was emboldened to install it myself because of the simplicity and logic of the system,” says Agnew. “We installed two Maretron screens, one above the companionway, and one down below in the nav station. It took me about twenty-five minutes to hook up the first sensor (at the top of the rig), ten minutes for the second, and five seconds for the third.”

In addition to using the Maretron displays for monitoring windshifts, Agnew integrated the wind data into his laptop, which was running Nobeltec navigational software, and MaxSea tactical software from Furuno. This required a converter that translated the NMEA 200 data into NMEA 0183 data, but once that was up and running, everything worked fine, and according to Agnew, the data the routing software got from the windspeed/direction center was perfect.


Another owner using a Maretron unit is Ray Peterson on his Swan 46 Cygne. Peterson has done the last two Bermuda Races and a lot of buoy racing with the WSO 100 sensor since installing it in 2006. “My boat had 20-year old B&G and I wanted to update,” says Peterson. “One of the reasons I chose Maretron was the fact that it was running on NMEA 2000. When I bought the system, NMEA 2000 wasn’t all that popular, but I didn’t want to get stuck in somebody’s dedicated network, plus it was very easy to install. I also liked the fact that there were no moving parts in the masthead system. The final reason was price; the system I purchased was much more affordable, especially because you don’t always have to replace moving parts.”

Peterson installed the masthead system himself but had a dealer run the wiring. He says it was a relatively simple install for them, and took less than a day, and that included the masthead wiring and a depth sounder.
Like Agnew, Peterson uses MaxSea routing software. “I wanted to go with the NMEA 2000 because electronics are always changing, and you don’t always want everything from the same manufacturer. We hooked it up, plugged it in, and the software saw the data and started working instantly. I was surprised. There was not one hitch then, and there haven’t been any since.”

Peterson has been pleased with the accuracy of the unit even during some hard-core conditions he experienced last summer. “We got caught in a squall,” says Peterson. “We had 50 to 60 knots of wind and everything worked well.”


Courtesy of Airmar| |****|

Maretron’s main competitor in this niche market is Airmar, which manufactures three types of sensor, the LB150, designed as an at-home weather station, the PB150, designed for recreational powerboats, and the PB200, designed for large commercial vessels and powerboats. Unlike Maretron, they describe their units as being designed for power and commercial vessels, although their units are also designed to work at a 30-degree angle of heel as well. The main difference for racers is that the Maretron unit, thanks to a design team at the University of Phoenix, is far more aerodynamic than the Airmar unit, which is more barrel shaped. In addition, the Airmar unit uses four sensors rather than three, and incorporates more electronic hardware in the unit, such as a GPS receiver, an accelerometer, and an electronic compass sensor.

There are two sides to every coin, however, and reps at one of the premier manufacturer of traditional cup and vane sensors scoffed at the idea of any transducer-type unit being superior. One representative we spoke to told us there was no way either transducer sensor was as capable, especially at an angle of heel. As he pointed out, no high-profile race program [that he was aware of] is using any one of these sonic sensors, and the latest and greatest, most technologically advanced raceboat, BMW Oracle’s new catamaran, actually has two cup-and-vane units on its masthead.

While cup-and-vane sensors will no doubt reign supreme for some time, one can’t ignore the fact that, until a few years ago, people looked down on ultrasonic speed sensors mounted on hulls for boatspeed. Now there are very few high-end race programs using paddle wheel speedos. The time may not have come for complete market domination for ultrasonic windspeed and direction sensors, but it may happen sooner than you think.


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