True Wind - your definition.

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


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Richard10002

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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.

So the industry standard means that the true wind for a boat in a faster flowing current in the middle of a river is different to the true wind for a boat half a mile away in the slower flowing current, (or back eddy), at the edge of the river?

Presumably, there is also a "Meteorological true wind" which is the same as the industry standard "ground wind"? In which case there can be two ways of defining true wind, hence the question in the OP, and neither is wrong.

I spent 6 years on Merchant Ships between 1978 and 1984, trained to the level of 2nd Officer, (Foreign Going), and did a degree in Nautical Studies. I've since been sailing for most of my life, (5 decades at least). At no time during my time have I ever heard, or considered, that True Wind is anything other than the wind over the ground. I don't think I have ever considered anything described by instruments as true wind as the "real" true wind, knowing instinctively that there is an unknown component missing. I have never thought along the lines of an industry standard, or even been aware of it.

I hope that sailing schools spend a bit of time talking about the differences between Meteorological True Wind and Industry Standard True Wind - it certainly wasn't covered when I did Yachtmaster at the same time as my wife did Competent Crew, and a couple doing Day Skipper helped during my exam.
 

johnalison

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I hope that sailing schools spend a bit of time talking about the differences between Meteorological True Wind and Industry Standard True Wind - it certainly wasn't covered when I did Yachtmaster at the same time as my wife did Competent Crew, and a couple doing Day Skipper helped during my exam.
My trouble is that I can't imagine myself while on passage asking my crew for a report on the "meteorological true wind" or "industry standard wind". Life isn't like that, and we need simple terms for simple sailors. Many of the forum members have drifted fairly easily into using True wind and Ground wind for normal use on sailing craft, and whatever the rights and wrongs, usage will always prevail.
 

Mark-1

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Just did a quick google and am amused to find that inconsistent application of definitions is a problem that goes beyond BW posters:

If an instrument for measuring the speed and direction of the wind is mounted on shore, then the readings obtained are those of the speed and direction of the true wind.

https://support.garmin.com/faqSearch/en-US/faq/content/lQFTLBSlv73TYGsOpDB7P6


Many of the forum members have drifted fairly easily into using True wind and Ground wind for normal use on sailing craft, and whatever the rights and wrongs, usage will always prevail.

That's my take, I'm just going to try to use "ground wind" for true wind in future. Not that it really matters, I don't recall any issues in the past.
 
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flaming

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So the industry standard means that the true wind for a boat in a faster flowing current in the middle of a river is different to the true wind for a boat half a mile away in the slower flowing current, (or back eddy), at the edge of the river?

Yes exactly. It would be a nonsense for it to be anything else, as that is the measure for the power available to your sails.

Remember why wind instruments were first developed, it was all about helping racing sailors make decisions about sails and allowing us to use polar diagrams to check we are going as fast as we should be going. All of which references the True wind as indicated by the industry standard. The ground wind is of no use when working out if you could be going faster in this wind strength.

Presumably, there is also a "Meteorological true wind" which is the same as the industry standard "ground wind"? In which case there can be two ways of defining true wind, hence the question in the OP, and neither is wrong.
Yes, the met office will (obviously) predict the Ground wind. But then they just call it "wind".

I hope that sailing schools spend a bit of time talking about the differences between Meteorological True Wind and Industry Standard True Wind - it certainly wasn't covered when I did Yachtmaster at the same time as my wife did Competent Crew, and a couple doing Day Skipper helped during my exam.

I actually don't think it's very important. You don't need to understand it to be safe, as any change in wind strength or direction will be fairly gradual and relatively small, but it's an interesting topic for the cruiser. Understanding it is however vital to anyone that races in tidal waters and has been a topic of discussion in every coaching event I've ever been to.
 

noelex

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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.

+1. A good explanation.

Yes exactly. It would be a nonsense for it to be anything else.

"Nonsense" is a bit overstating the case. True wind is more useful racing, but I think ground wind is more useful than true wind to the cruising sailor, especially as the ground wind display is likely to be much more accurate than the true wind display.

After all, judging from the poll results about 50% of YBW members think their instruments are displaying ground wind when the true wind option is selected.
 

Pye_End

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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.

That is not really what I am trying to get at. Accuracy of data is irrelevant when it comes to field definitions. What I am saying is that with GPS, logs, wind instruments, integrated systems, we have access to levels of data never seen before, so instrument makers use definitions of what they display. The definitions are the ones indicated by flaming.
 

Mark-1

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After all, judging from the poll results about 50% of YBW members think their instruments are displaying ground wind when the true wind option is selected.


Plus in the recent discussion about a discrepancy between true wind measured from 3 yachts and ground wind measured from Bramblemet nobody even thought to mention the distinction. They either weren't aware of the distinction or thought it was so insignificant that couldn't account for a small over read.

http://www.ybw.com/forums/showthread.php?490102-Bramblemet-under-reading

Which isn't that surprising because few people really trust their anemometer or log. ...and flux gate compasses have approx +/- 3 degree error.

All of which adds up to this not being the most important topic ever discussed on YBW. I'm still enjoying it.

At no time during my time have I ever heard, or considered, that True Wind is anything other than the wind over the ground. I don't think I have ever considered anything described by instruments as true wind as the "real" true wind, knowing instinctively that there is an unknown component missing. I have never thought along the lines of an industry standard, or even been aware of it.

Ditto. I did understand how most plotters calculate 'True Wind' and just assumed everyone was happy with it being a bit rubbish. (In fact, I've yet to rule out that being the case.)
 
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Mark-1

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Just did a quick google and am amused to find that inconsistent application of definitions is a problem that goes beyond BW posters:

If an instrument for measuring the speed and direction of the wind is mounted on shore, then the readings obtained are those of the speed and direction of the true wind.

https://support.garmin.com/faqSearch/en-US/faq/content/lQFTLBSlv73TYGsOpDB7P6

Why is this inconsistent? All it says is Ground Wind = True wind if the sensor is not subject to tides/current/movement etc.

I take your point about that.
 
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Dictys

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The IMO's view is

"True wind speed and direction means wind speed and direction which are not reflected by ship’s speed and heading.
Relative wind speed and direction means wind speed and direction which are reflected by ship’s speed and heading
."

Nothing about any other type of wind or measuring over ground, sea, currents, tides.

In my view it would be the true wind speed and direction measured over a fixed position on the earth's surface. i.e ground as the wind speed and direct is not by ship’s speed and heading.
 

lw395

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The IMO's view is

"True wind speed and direction means wind speed and direction which are not reflected by ship’s speed and heading.
Relative wind speed and direction means wind speed and direction which are reflected by ship’s speed and heading
."

Nothing about any other type of wind or measuring over ground, sea, currents, tides.

In my view it would be the true wind speed and direction measured over a fixed position on the earth's surface. i.e ground as the wind speed and direct is not by ship’s speed and heading.

The IMO is mostly concerned with ships which go several times faster than the tide or current, so the tide vector would be lost in the measurement uncertainty for most practical purposes.

There was a thread on here recently arguing the toss about Bramblemet.
A good illustration of the futility of worrying too much about a 1 or 2 knot tidal effect on the wind.
 

bdh198

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... 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.

+1

Those are the only three winds I care about when sailing. The naming of those definitions could have be clearer (water wind or tidal wind instead of true wind?), but once understood they shouldn't cause any particular difficulties - unless, of course, you're a trained meteorologist coming to sailing after a lifetime of using "true wind" to mean something up in the atmosphere.

It's been a long time since I did any RYA courses, and was never taught about the difference between ground wind and true wind. It's an important distinction to understand, particularly if your calibrating on board instruments. I hope this is a distinction the RYA now explain in their training courses (and use the same terminology to Flaming, which is what I now use).
 

eigerwand

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I know of three winds.

The wind I can beat into at 30 degrees. This wind is really windy when I sail into it and rather disappointing when I sail downwind.

The wind I can beat into at 45 degrees. I like this wind as it stays the same whatever direction I sail in.

Bramblemet. This is used to decide whether I shall go sailing or not. I wouldn’t have much of a clue what angle to sail into it...
 
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pyrojames

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I am sure we went through this all many years ago. I find it percular that the true wind should be dependant on your observation platform. I would expect that anything that was "true" was not subjectively true. Perhaps in the modern vernacular it should be alt wind. :)

It may we'll be the case that sailors have adopted the term true wind as a result of a lack of instrumentation. Now that the instrumentation exists to measure all the subjective variables, it would make more sense to define the true wind as the one that is not subjective. If you want to consider the wind that you feel with no way on, then this would surely be a sailors wind, as no one else really cares. Knowledge of tide, bearing and true wind would allow you to calculate you best course to destination.
 

Alan ashore

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I'm wondering what name those who have chosen "relative to fixed point attached to the Earth" would use for the other wind? (Presently a majority of respondents, which I find slightly surprising incidentally)

"Effective Wind" and "Sailing Wind" are both terms I've come across from time to time, and even used myself on occasion to avoid misunderstanding when talking to someone in that camp.
 

Mark-1

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I'm wondering what name those who have chosen "relative to fixed point attached to the Earth" would use for the other wind? (Presently a majority of respondents, which I find slightly surprising incidentally)

Never thought about it. Forecasts give me ground wind, which I'm satisfied with. When I'm on the boat I'm sailing to apparent wind and don't care about the factors creating the wind. I'm really struggling to think of a time I've factored (say) 2 knots of tide generated windspeed/angle into any decision in such a formal way that I needed a name for it. (Maybe I'm factoring it into decisions unconsciously.)

The only verbal reference I can think of to the wind the tide's making are on light/heavy days sailing long distances across tide when I might think to myself 'Cheer up it'll increase/drop 4kts over the next couple of hours'. (But a pedant might say I'd be cheering up about the apparent wind increase/decrease.)

Now I think about it don't know anyone who corrects forecasts for tide either - if it's important, you'd think they would.

I also have to say I'm deeply cynical about all the reasons for needing a "wind with tide effect factored in/out" number apart from the polars one and I'm a little bit cynical about that because I don't trust the kit that makes the measurements of heading, speed through water and wind speed to be accurate. I think on most boats if you significantly change course with 'True Wind' showing on instruments you see that 'True Wind' suspiciously change value which suggests to me the inputs are wrong.
 
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flaming

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I also have to say I'm deeply cynical about all the reasons for needing a "wind with tide effect factored in/out" number apart from the polars one and I'm a little bit cynical about that because I don't trust the kit that makes the measurements of heading, speed through water and wind speed to be accurate. I think on most boats if you significantly change course with 'True Wind' showing on instruments you see that 'True Wind' suspiciously change value which suggests to me the inputs are wrong.

If you race on a boat where the TWD and TWS change significantly between tacks, or between upwind and downwind, you soon learn the value of well calibrated instruments...

However, even with badly calibrated instruments, they are at least normally repeatable. Which means that if I'm going upwind and my TWS says 10, then even if it's not actually 10, it will still say 10 the next time I have the same wind. Which is kinda the point... Because if you then use ground wind saying "my GPS is more accurate, so this is better" then whilst it might be closer to the correct value of ground wind than your poorly calibrated log based True wind is, it is subject to showing the same value when the wind you're actually sailing in has changed because the tide has turned. And that's no use at all if what you're trying to do is check that for a given windspeed recorded by your instruments you are going as fast as you were earlier.
 
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