True Wind - your definition.

[laika]

who said there was no place for postmodernism in anemometry?

 

[davidmh]

John 32i is correct The true wind is what you feel when a boat is stationary to the earth and Apparent wind is the wind that you feel when the boat is moving. When sailing it is the apparent wind that the sails feel.
David MH

 

[lw395]

who said there was no place for postmodernism in anemometry?

Probably someone confused between Marcel and Leon Foucualt?

 

[Richard10002]

Lets say that it's slack tide, and there is no wind, (True wind (= Ground wind) = zero). Lets say the tide begins and runs a 6 knots for an hour - the boat begins to move with the tide at 6 knots, so the wind it feels is 6 knots and, if it points itself in the right direction, with the sails up, it will begin to move at an angle to the tide - surely the wind it is feeling is apparent? The reality is that there is no wind, so any wind felt can only be apparent. There will then be a change in this apparent wind due to the boat moving.

For my own purposes, and I am sure they will align with many, (66% of pollsters here?), is that true wind is the wind caused by the weather. The wind caused by a boat under way in a current/tide, but not making way, is apparent wind, and any change in the apparent wind caused by a boat moving through the water is also apparent wind.

If I ever enter an arena where some might add in the term ground wind for my true wind, I'll be sure to ask some questions. A bit like asking what chart datum is being used when quoting a position.

I'm still struggling to understand why the matter did not crop up in my professional training, a degree course, (where you would think that this kind of minutiae would be lapped up), and Yachtmaster preparation and exam?

 

[Malo37]

I'm surprised at some of the comments on this thread in that sailors don't know what true wind actually is.
True wind speed and direction is nothing to do with boats, currents etc. It is what you would experience if you were stationary with respect to the Earth. The ability of your instruments to calculate that accurately on a moving boat is another matter.

 

[anoccasionalyachtsman]

John 32i is correct The true wind is what you feel when a boat is stationary to the earth and Apparent wind is the wind that you feel when the boat is moving. When sailing it is the apparent wind that the sails feel.
David MH

So what would you call the wind that you can feel and measure when you're not moving through the water but the water is moving with the tide? This is the wind vector that may not be important to you, but those of us that race and or plan our cruises for best performance absolutely need to know it.

 

[johnalison]

So what would you call the wind that you can feel and measure when you're not moving through the water but the water is moving with the tide? This is the wind vector that may not be important to you, but those of us that race and or plan our cruises for best performance absolutely need to know it.

Quite so. The problem is not, for the most part, a lack of understanding on most people's part but a lack of suitable terms available. Further confusion is created by the value we attach to the word 'true'. The wind felt when stationary is no more 'true' than the wind felt when sailing, which we choose to call 'apparent'. When I feel the apparent wind, it feels quite true to me at the time. All we need to do is to rename the three winds wind A, B, and C and Bob's your uncle and all confusion disappears. Only joking of course, but people are only getting emotional because they have formed an attachment to one or other term. The purpose of language is to communicate, so, if someone thinks that what they say is worthwhile, it is their responsibility to make clear in which sense the term they use is to be understood.

 

[Yealm]

Oops I’m afraid you’re wrong

1) Ground Wind is the wind you feel due to atmospheric conditions (measured with anemometer and GPS).

2) True Wind is the wind you feel due to atmospheric conditions and motion from boat motion relative to water ( measured with anemometer and paddle wheel).

3) Apparent Wind is the wind you feel due to atmosphere, current motion and boat motion combined (measured with anemometer).

I'm surprised at some of the comments on this thread in that sailors don't know what true wind actually is.
True wind speed and direction is nothing to do with boats, currents etc. It is what you would experience if you were stationary with respect to the Earth. The ability of your instruments to calculate that accurately on a moving boat is another matter.

 

[bbg]

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.

I would give you a +1 but someone has already done that, so I'll give you a +2.

People can debate this all they like but the instrument makers use True Wind to mean the wind relative to the surface of the water. I am not aware of any instruments that offer the ability to show the wind relative to a fixed point on the earth. Probably because that is largely irrelevant to sailors. Not entirely irrelevant but largely irrelevant most of the time.

As of right now, 63.49% of the respondents to the poll are using the wrong terminology, according to the instrument makers.

 

[Malo37]

Oops I’m afraid you’re wrong

1) Ground Wind is the wind you feel due to atmospheric conditions (measured with anemometer and GPS).

2) True Wind is the wind you feel due to atmospheric conditions and motion from boat motion relative to water ( measured with anemometer and paddle wheel).

3) Apparent Wind is the wind you feel due to atmosphere, current motion and boat motion combined (measured with anemometer).

Oops, I'm afraid your common sense has deserted you.
GPS is nothing to do with it. Wind was around quite a bit before GPS was invented. (and indeed anemometers)
Your peculiar definition of true wind 2) is precisely what I said. It is the wind speed and direction measured relative to a fixed point. How that wind was generated at that particular location is irrelevant. The same applies whether you are on land or water.

 

[noelex]

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.

This is the main problem associated with displaying true wind on a cruising yacht. Switch to ground wind and all the inaccuracies associated with the log measuring STW are eliminated .

Unfortunately, many of the older instruments cannot be switched to ground wind, but if this is an option on your instrument package, it is certainly worth a try. If you change to ground wind you will find the display will stay much more constant with changes in course. Even removing the paddlewheel will have no effect on the reading.

 

[noelex]

Oops, I'm afraid your common sense has deserted you.
GPS is nothing to do with it. Wind was around quite a bit before GPS was invented. (and indeed anemometers)

Yealm is correct. To calculate ground wind on a boat, GPS input, specifically SOG, is needed.
Wind instruments can only measure apparent wind. On a fixed land location apparent wind speed = true wind speed = ground wind speed, but this is not correct when moving,

 

[Richard10002]

I would give you a +1 but someone has already done that, so I'll give you a +2.

People can debate this all they like but the instrument makers use True Wind to mean the wind relative to the surface of the water. I am not aware of any instruments that offer the ability to show the wind relative to a fixed point on the earth. Probably because that is largely irrelevant to sailors. Not entirely irrelevant but largely irrelevant most of the time.

As of right now, 63.49% of the respondents to the poll are using the wrong terminology, according to the instrument makers.

But not according to 63.49% of the respondents to the poll, including me.

The fact that the instrument makers have chosen to call a wind something that it is not, because it suits their marketing machine, does not make it right. True means true, and apparent means apparent... it's hard to see how apparent, under certain circumstances, can mean true. It can be called "true", but it wont be "true".

They could quite easily have called the wind felt by a yacht, moving through the water, true wind, and it would have been as correct as calling it the wind felt when moving with water, but not through it.

 

[GrahamM376]

"Glossary of Meteorological Terms" has this to say -

True wind direction
The direction, with respect to true north, from which the wind is blowing. Distinguish from magnetic wind direction. In all standard upper-air and surface weather observations, it is true wind direction that is reported.

 

[Mark-1]

As of right now, 63.49% of the respondents to the poll are using the wrong terminology, according to the instrument makers.

Presumably because before GPS you couldn't factor tide out, so true wind with tide was a close enough approximation having said that both definitions seem to be in use by YBWers so I'm not sure you can say either is 'wrong'.

If we wanted to decide which is 'right' I guess you have to decide who the final arbiter of English Language marine terminology is. I'm really not sure who that would be.

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. .

Apparent wind works fine for that purpose.

 

[lw395]

"Lay lines" is another term the marine electronics industry has chosen which I find unhelpful. I guess it was chosen because it sounds quite nautical and it does get the message across. However when heard spoken it sounds like "ley lines" which on first hearing sounds a bit new age and just prompts a needless WTF discussion. (Maybe it's only a thing in the UK.)

"Lay Vector" doesn't have the same nautical ring but it's unique, and I'm sure marketing departments could come up with something even better than that.

'Lay line' is a common sailing term which was in use long before any marine electronics.
It was certainly common in dinghy racing when I was a student.
A lay line is not a vector.

 

[Tomahawk]

I understand it... on my Raymarine ST2 90 system which gives true, apparent and ground
True wind is the angle of the wind onto boat after taking account of boat speed. But I am not sure about tides
Ground wind is what the weather forcast predicts.

The plotter shows ground wind
The displays show true and apparent

 

[Mark-1]

'Lay line' is a common sailing term which was in use long before any marine electronics.
It was certainly common in dinghy racing when I was a student.

Thanks for correcting me. I've sailed in one form or another since I was 3 including a vast amount of dinghy racing as a youngster and I hadn't heard the term 'till it turned up on a plotter. So I thought I was on safe ground with that assertion.

EDIT: Just googled and referred to my (very well read) 1975 copy of Dick Tilman's 'Laser Sailing' and I now have a red face.

 

[prv]

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."

And since they don't specify whether they mean ship's speed through the water or ship's speed over the ground, that provides no clarification at all. It fits either definition of "true wind" being used on this thread, depending on which definition of ship's speed you think they mean.

Pete

 

[Yealm]

I’m sorry but you are still confused about the terminology used.

To measure atmospheric wind speed you need to take into account your own motion. To do this on a boat you need GPS- the calculated wind speed is called Ground Wind.

True Wind is an approximation to Ground Wind - but as it uses paddle wheel speed, it fails to take into account boat motion due to tide. It is called True Wind because for many years prior to GPS it was the ‘true-est’ we had and much closer to atmospheric wind speed than is apparent wind.

If you still don’t believe us, perhaps check it out on google -we may be the 35% minority view but we’re still correct!

Oops, I'm afraid your common sense has deserted you.
GPS is nothing to do with it. Wind was around quite a bit before GPS was invented. (and indeed anemometers)
Your peculiar definition of true wind 2) is precisely what I said. It is the wind speed and direction measured relative to a fixed point. How that wind was generated at that particular location is irrelevant. The same applies whether you are on land or water.