True Wind - your definition.

When you use the term 'True Wind' do you typically mean:

  • Wind relative to a fixed point attached to the Earth.

    Votes: 85 67.5%

  • Wind relative to an point moving with the current/tide.

    Votes: 41 32.5%
  • Total voters
    126
Mark-1

Mark-1

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The recent Lee Bow thread got me wondering what definition of 'True Wind' people use. I'd only ever used/heard one defintion before and was suprised to find other people using a different one. I'm wondering how widespread that useage is.

If your useage changes with context, just vote for the one you use most.
 
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True wind is the wind that you feel if you are not moving...the wind that blows across the land (or water) and the one the weather forecasts refer to!
 
John 32i said:
True wind is the wind that you feel if you are not moving...the wind that blows across the land (or water)
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Ah, but the problem (I assume, having not read the other thread) is that the wind that blows across the land can be different to the wind that blows across the water. The water could be moving, but the land is not.

Raymarine in their early Seatalk instruments defined true wind as relative to the water, because they could get a water speed feed from the log instrument but ground speed wasn’t available because GPS wasn’t yet generally fitted to yachts. This is still the definition they use. Others may vary, hence the question. It could make a big difference in somewhere like the Alderney Race.

Pete
 
No I think that's ground wind.

True wind is the wind measured on a boat and is the vector combination of ground wind and wind created due to movement by tide. I think !

John 32i said:
True wind is the wind that you feel if you are not moving...the wind that blows across the land (or water) and the one the weather forecasts refer to!
Click to expand...
 
Now that we have instruments on board that can differentiate between all these different things, they need a clear terminology to define them. Ground wind is relative to the wind, and true wind is relative to the patch of water you are sailing on at the time, as this is how the instruments define them. Using the terms in any other way now just leads to confusion.
 
Yealm said:
No I think that's ground wind.
...!
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Not to be confused with the sky wind presumably?

There is no 'true' wind.
If you are getting hung up about the differences between the two definitions, your view of what wind is really like is just hopelessly simplistic.
 
Pye_End said:
...as this is how the instruments define them.
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Then that true wind would vary depending on the quality of the measurements which isn't right. The true wind should be independent of your instruments, it's the same regardless of the equipment used. The variation is in your measurement of it, not the wind itself.

The log is especially tricky as it presumes the boat to be moving forwards through the water, when it doesn't.
 
My simplistic view : "There are several ways to define the wind. For weather work at sea we care only about the true wind. This true wind is the speed and the direction of the wind relative to the fixed earth under the ocean. Tied up at the dock, we feel the true wind. Once we get underway, however, our own motion changes the wind we feel, and then it is called the apparent wind."
 
Mark-1 said:
When you say that, do you mean there's no Wind relative to a fixed point attached to the Earth or no Wind relative to a point moving with the current/tide? :D
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I mean that by the time you've measured either and told me, the truth will have gone out of it!

Just to make things clear, did you mean the current at the surface that's been affected by the wind, or the true current deeper in the water?
 
lw395 said:
Just to make things clear, did you mean the current at the surface that's been affected by the wind, or the true current deeper in the water?
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I meant the current at the point of measurement or the point of prediction but who knows if that's right. It's an interesting question because I have no idea if (say) tide diamonds refer to tide at the surface or (say) 3m down in completely undisturbed water.

Your question raises the same question about ground wind, which had hitherto seemed unambiguous to me.

Loving this topic. The more I think about it, the less I know. :D
 
Not sure what the issue is here?

True wind is "True Wind". If you are stationary on a fixed piece of land, (real or imaginary, you might be anchored), you feel the true wind.

If you are floating on water, perhaps described as under way, but not making way through the water, and there is a current, you feel the wind relative to the water. This is apparent wind. If you are making way through the water, you feel the wind relative to yourself with the combined effect of your motion through the water, and the motion of the water over the fixed earth. This also is apparent wind. The word relative is probably a good clue as to whether the wind is relative or true.

The pedantic could say that, as the earth is spinning, and hurtling through space, the wind described as true is also relative to something, and they are welcome to complicate, and perhaps distort things in this way, if they wish :)
 
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John 32i said:
My simplistic view : "There are several ways to define the wind. For weather work at sea we care only about the true wind. This true wind is the speed and the direction of the wind relative to the fixed earth under the ocean. Tied up at the dock, we feel the true wind. Once we get underway, however, our own motion changes the wind we feel, and then it is called the apparent wind."
Click to expand...

No, tied up at the dock we feel the ground wind.
Drifting with the tide we feel the true wind.
Sailing along we feel the apparent wind.

Remember, the only wind we can measure is the apparent wind. Everything else we display is a calculated field.

Here's a good article.
https://www.sailingworld.com/how-to/instruments-and-real-angles
Here's Raymarine's response to the same question.
http://raymarine.ning.com/forum/topics/true-wind-speed-calculation-and-gps-data
 
I think I use both definitions but may be even more complicated as when sailing I am not sure if my Wind instrument shows true wind using the GPS SOG and COG or my heading compass CTW and wheel log STW. One is accounting for tide/leeway and the other isn't. I assume it is using the GPS output. I must check as I think it is configurable.

When on land true wind to me is when I am standing stationary so a fixed point on earth.
 
neilf39 said:
I think I use both definitions but may be even more complicated as when sailing I am not sure if my Wind instrument shows true wind using the GPS SOG and COG or my heading compass CTW and wheel log STW. One is accounting for tide/leeway and the other isn't. I assume it is using the GPS output. I must check as I think it is configurable.

When on land true wind to me is when I am standing stationary so a fixed point on earth.
Click to expand...

If your instruments call it True Wind, or TWS/TWA, then it is calculated using the speed through the water and the heading. That is the industry standard.
The industry standard is that wind calculated using GPS data is called ground wind.
 
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