Calculating True Wind

[Joe Mullee]

I've never had a wind instrument on board my boat but would like one. I also don't have a speed instrument on board my boat and don't see the need for one for the type of sailing I do in the Chesapeake. I do have a Garmin176 GPS that is not integrated with my only other two instruments which are the Raymarine ST60 depth finder (using an in-hull transducer) and a Raymarine X5 Smart Pilot.

My question is if I purchase a wind instrument must it either be hooked up to a GPS or to a speed instrument in order to calculate True Wind?

Sorry for my ignorance.

Joe Mullee

 

[tommays]

Yes or you will only get apparent

 

[Stu Jackson]

You need boat speed, boat heading, apparent wind direction and apparent wind speed to calculate true wind direction and speed.

http://deniswee.net/ApparentWind/trueapp.htm

 

[Joe]

Joe...... all you need is a simple boat compass to determine true wind direction while sailing. Sail close hauled on both tacks, port and starboard: record the compass headings... then average the two for your true wind direction. example: sailing closehauled on port tack 270 magnetic, then over to starboard.. 180 magnetic. the true wind would be 225 magnetic.

(Your GPS may have an "average heading" ,or similar, feature on it that may help in determining true wind direction.)

Keeping track of your headings on each tack will tell you how much the wind direction is changing.

Instrument wise, you need a speed log that will communicate with your wind instrument to calculate true wind.

There are mathematical models available..... just google "apparent vs true wind"

 

[Benny17441]

True wind is usually perpendicular to the waves and behind the apparent wind. A fair approximation works for me.

 

[Witzend]

It not just angle, but speed as well. I find the data useful when motoring either close to into or DDW in determining if I have enough wind to set sail. After all that is why I'm out there in the first place. Often I have to use my senses, (sea state) anyway because the critters are having a party on my speed transducer.

 

[Ted]

Here is a link to a wind direction calculator.
http://www.sailingusa.info/true_wind_calculator.htm

 

[Dan Johnson]

Joe...

you could buy one of the inexpensive Moor apparent wind instruments and come to a stop every time you wanted to know the "True Wind"...:dance:

 

[Ross]

Re: Joe...

If you have a gps then you can determine your speed through the world. The wind speed and direction is then just a problem of solving the vector.

 

[Scott T-Bird]

I have a wind instrument and love having it. I also have the speed instrument. But my wind is Simrad IS 15 and the speed is Datamarine. Both work perfectly but aren't wired to talk to each other. I was wondering if they can thru NMEA 0183.

That said, I find no need to think about true wind, either speed or direction. It is the apparent wind that impacts my sailing decisions. I can tell what the true wind is when I'm at the dock, otherwise it matters little. Adapting to apparent wind while sailing seems to be the important issue, no?