Calibrating wind speed instruments

[gunnarsilins]

When reading instructions for this from various sources, the common recommendation seems to be to use a good anemometer, held at the same height as the masthead unit.
I´m not particulary fond of this method because;
a) I don´t own any anemometer, nor do my friends
b) I don´t really enjoy climbing 16 metres of mast

Why not pick a calm day and motor at a fixed speed and calibrate the wind instrument after the log, or the SOG value on the GPS?
On my old B&G Hornet the windspeed intrument already gives the values in knots, so no re-calculation is needed.
If the boat goes 7 knots, the wind must be 7knots!?
Or have I missed something?

Further, if I´m not entirely sure there is absolutely no wind (there might be some 16 metres up in the air) when doing this, I could go various courses and average the setting?

Anyone, any thought about this?

 

[tom52]

The method you describe is more or less exactly the recommended method described for calibration in my Navman 3100 handbook.

 

[Reap]

Quote:
________________________________________
If the boat goes 7 knots, the wind must be 7knots!?
Or have I missed something?
___________________________________________

Tide?

You could be waiting a long time for a completely calm day

Why not calibrate it against other yachts in the mooring/marina?

 

[johmal]

Yes you missed something.

GPS is pretty good for measuring speed over the ground. When used with a log it allows you to calculate leeway!

If it's handheld you can also use it to calibibrate your car speedo - but make sure you remembered to change the readout to give you MPH, and get someone else to drive while you are doing it! Make sure the road is flat and straight.

John M

 

[stamfordian]

1/curry......force seven
2/bean,s....force six
3/bitter(real ale}... force five
4/bitter(keg).....force four
5/guiness... force three
6/lager...force two
7/mild ale...force 1









sorry couldn,t help myself...............

<A target="_blank" HREF=http://www.arweb.co.uk/argallery/stamfordian>http://www.arweb.co.uk/argallery/stamfordian</A>

 

[Trevor_swfyc]

Sounds good to me if you use GPS for speed then this is SOG no worries about tide.
Even if you have slight airs if you go upwind and downwind at 5 knts then the average on the wind instrument should also be 5 knts. If the reading is say 6.0knts into the wind and the average is 5.4 knts head into the wind again at the same speed and set to 5.6 knts. This would give the average of 5.0 while it may be correct at 5.0 knts I suspect it might be slightly out at 10 knts. Not sure if they quote accuracy at various speeds but then its not that critical is it?
I set up my LOG in a similar way against the GPS.
Good luck
Trevor

 

[gunnarsilins]

It seems that....

....my thoughts for once went into the right direction!

As somebody wrote, 100% accuracy is not really needed, and finding a calm day wouldn´t be too hard. Neither do I need to bother about tide in Stockholm, and the SOG function on the GPS would take care of that anyway.

Unfortunately my boat sits in about 30 cm solid ice at the moment, so I beleive I´ll have to wait for some time doing the calbration!

Thank you all!

 

[Stingo]

This is probably completely untrue but it sounds good so I believe every word of it. Legend has it that Admiral Beaufort, or whatever his rank was, drank copious amounts of an evil concoction of Rum and Pernod which caused him terrible flatulence. The more he drank, the more wind and thunder he produced. Storms so putrid that it brought tears to the eyes of any unfortunate crew member to leeward of him. Now when Mother Nature did her best to out perform the man, Beaufort's crew would observe that it was only a force 8 on the his scale

<A target="_blank" HREF=http://www.stingo.co.uk>http://www.stingo.co.uk</A> - now showing at a computer near you

 

[Chris_Stannard]

There are three aspects to this, IMHO.

First the wind at the masthead is going to be stronger than that on deck because of the friction at the surface, so using a anemometer other than at your masthead height is always going to be a no, no since iit will not be accurate.

Second, what the little contraption at the top of the mast does, is whizz round in proportion to the incoming weight of air. Since the size of the little scoops and the length of the arms are fixed, the manufacturer will have set it up so that it counts the appropriate number of pulses for a wind speed which he will have tested. Therefore as long as the unit is in good order (it does not have a stiff or worn bearing) the answer it is giving you is likely to be correct for the wind it sees. You have to remember that the airflow round the mast head modifies the overall airflow so that, as your sensor protrudes from the masthead it will be more accurate going to windward and much less so going down wind. The downwind reading may be as much as 20% low and this can breed a false state of confidence going downwind in a strong breeze.

Third. I do not rely on the wind indicator to tell me when to reef, I use the rule that the time to reef is the moment you first think, "I wonder if I ought to put a reef in?" That is why I say watch out for the downwind situation. I also tend to reef before it gets dark if I think the wind strength may increase.

On this basis my advice to you would be to calibrate the wind angle and leave the wind speed on the manufacturer's default setting.

Lets hope we all have a good season.

Chris Stannard

 

[gunnarsilins]

Chris!

Thats exactly what I wrote, I don´t much look forward to climb the mast, even if I could lay my hands on a anemometer.

I agree in your opinion regarding reefing. Would never use the instruments for a decision.

The reason for recalibrating is that the old B&G Hornet 4 system I have on my boat has been repaired and various bits and pieces has been exchanged. So in this case there is no facrory calibration to stick to.

I admit, the need for a wind speed instrument is quite doubtful, but if it´s alredy there with its nice dials, why not calibrate it so it at least shows something close to reality?

 

[Chris_Stannard]

Re: Chris!

Best answer I would suggest then is to go out in company with another boat with about the same mast height and sail about 50 metres apart into the wind, with the windward boat a bit behind the leeward one so you do not get cross interference.

Tou friends anemometer should then give you a close enough reading to set yours up.

Hope this helps

Chris Stannard

 

[Guest]

Gunnar???

Hi Gunnar, I also have a B&G Network system on my yacht in Sweden. The Wind does not show any windspeed at all. Unfortunately B&G are not currently represented in Sweden. As one option I can send it to B&G Service in the UK but I prefer if I can repair it in Sweden. Were did you repair your wind system /// Patrik

 

[gunnarsilins]

B&G in Sweden

Jag antar vi kan skriva pa svenska!
In case not, let´s stick to English.

I have done the repairs myself, I had a Hornet 4 installed when I bought the boat, with the sailing monitor at the chart table and a digital multi-function repeater in the cockpit. The wind speed function did not work at all and the repeater had some faulty switches.
I found a second hand kit, complete with sailing monitor, 4 analogue repeaters and all transducers very cheap from a guy who wanted to upgrade his boat.
So out of this I made a complete kit, with the analogue repeaters instead of the digital one.

Probably (if there´s no fault in the wiring) your fault is a reed relay in the wind transducer which is defect, this is a well known weakness.
The sailing monitor can be checked by shorting the black and the purple wire going to the wind transducer. If you short these wires, release them, short them again and repeat as fast as you can....you´ll simulate the the reed relay closing and you should see some 'wind speed values' on your monitor.
This way you can establish if it´s the wiring, instrument or transducer which is faulty.
If you don´t want to dismantle the transducer or fiddle with wires yourself contact:
Ingeniorsfirman Marinelektronik
Tavelsjovagen 18
121 72 Johanneshov
tel. 08 645 55 44

These guys (ask for Anders or Lasse) are as far as I know not authorized by B&G, but nevertheless they are good at this stuff.

Lycka till!

Gunnar

 

[Reap]

Re: B&G in Sweden

Still can't see why you can't just calibrate it against another yacht or preferably two with wind speed instruments already working and moored close by.

<A target="_blank" HREF=http://www.yacht-links.net>http://www.yacht-links.net</A>

 

[gunnarsilins]

I agree, but....

....if the wind is not steady, which it normally isn´t, I can imagine there will be a lot of shouting from the neighbouring friends. Also, if their instruments don´t give reading in knots, I´m not the man to do the fast re-calculations!

My idea was to make some good use of a calm day when I´m motoring anyway!

 

[gunnarsilins]

I agree, but....

....if the wind is not steady, which it normally isn´t, I can imagine there will be a lot of shouting from the neighbouring friends. Also, if their instruments don´t give reading in knots, I´m not the man to do the fast re-calculations!

My idea was to make some good use of a calm day when I´m motoring anyway!

 

[Reap]

Re: I agree, but....

hmmm...true, the wind is not always steady, though I wouldnt have thought it that difficult to get some steady moments. Though I confess Ive never tried it!
I thought all wind instruments were in knots?

<A target="_blank" HREF=http://www.yacht-links.net>http://www.yacht-links.net</A>

 

[charles_reed]

Whilst directional calibration is fairly common, speed calibration is definitely a chancy business.
Most anenometer cups, and the twin magnets inside them operate to far closer tolerances than you'll be able to reproduce.
If you suspect misreading check the rotating head - usually the most effective calibration method is to replace that.

It might account for the somewhat hit-and-miss calibration checks proposed.