[C38] Anemometer orientation

[David Epstein]

Steve,

For many years, we had a Signet anemometer on SuperStar, with the 
bracket and sensor mounted aft of the mast.  My late boat partner 
liked it there because he used it as a "Windex" as well.  When I 
upgraded the system to Nexus, we mounted the sensor forward of the 
mast (and installed a Windex aft).  Without question, the anemometer 
was much more accurate when the sensor was mounted forward.   I now 
experience significant discrepancies when going downwind, sometimes 
30 degrees or more.  You can see the difference in angles between the 
sensor and the Windex by looking at the top of the mast.

I am not sure if the type of sensor plays a role in the inability for 
the Nexus sensor to track correctly.  Instead of the more traditional 
spinning cups for wind speed and a vane for direction (such as the 
Signet), the Nexus has a sort of spinning vane that rotates towards 
the wind.

What many people do to mitigate the updraft problem is install the 
sensor on a carbon fiber wand, extending the sensor as much as 30" 
above the top of the mast.  I understand that this works, but the 
carbon wands are so expensive, I have not tried it as of yet.

I haven't noticed if the discrepancy is present when going downwind 
without a spinnaker, but I assume the chute either creates the 
problem or makes it much worse.

So, the short answer is that you may want to install your sensor aft.


David Epstein
SuperStar #122
Marina del Rey, CA



At 10:07 PM 2/22/2009, you wrote:

>When we had the mast down last year we installed the bracket and 
>pulled the cable for the later addition of wind instruments.  Now Im 
>ready to install them and going by the orientation of the bracket 
>the anemometer will point forward.  Im concerned about the proximity 
>of the vane and tri-cup to the head of the spinnaker.  Im curious 
>how others have them oriented.  The boat yard says they have never 
>seen them installed aft, but the signet literature shows aft.   Does 
>it make a difference?  those of you with them going forward have you 
>had any problems with the spinnaker?  As always Thanks.
>
>Steve
>Peregrine #312
>Seattle
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David Epstein
President, Sound Solutions
Chairman, CEA TechHome Division
Member of the CEA Board of Industry Leaders
Member, CEA Division Executive Board
Tel 310.398.0032
Fax 310.398.0036
www.soundsolutions.com
www.ce.org

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