True Wind - your definition.

[Richard10002]

No it is what nearly everybody with a jib and a compass has been calling true wind for the last 80 years at least.

Not me and, as I said earlier, I got 2nd Officer (Foreign Going), Certificate, in about 1983, a BSc in Nautical Studies a year later, and Yachtmaster in 2006. I have never considered True Wind to be anything other than what some are now calling Ground Wind, (a term I've never heard of before this thread), and it being anything different has not cropped up in any of my seagoing education.

So I have had a jib and a compass for about 45 of the 80 years you talk about.

I have also never seen an instrument which referred to Ground Wind, True Wind and Apparent Wind and I wonder if it is a feature that has actually arisen in the past decade as I havent been to sea since 2010, and havent experienced any instruments newer than about 2007.

In another post someone suggests "you are out of date", to a previous poster so, perhaps, I am out of date, but only to the tune of ten years max..

 

[lw395]

Nope, almost always awbv/gwtv. (True, to the faithful minority).

This is what they usually look like.

View attachment 67516

And here's one using apparent. Very odd.

View attachment 67517

If you look at the polars for my dinghy, the bottom half of the chart would barely exist if the angles were apparent. We reach 45 degrees up from dead down wind, with the apparent wind well forward of the beam.

 

[GrahamM376]

I have never considered True Wind to be anything other than what some are now calling Ground Wind, (a term I've never heard of before this thread), and it being anything different has not cropped up in any of my seagoing education.

If you had a flying rather than floating background then you would often have heard the term "surface wind" but never called ground wind. I'm with you in that True wind is as described in the Met. glossary. Any wind measured on something which is moving/drifting with tide is apparent wind.

 

[Mark-1]

No. Polars are always TWS and TWA. They would not work as apparent as you’d be chasing your tail.

It'd work fine. Indeed, you can easily convert them back and forth - obviously your plotter is doing the opposite calculation to give you TWS/TWA.

And they’d be innacurate with ground wind. If you do not see that there could easily be a 5 knot difference in TWS with the same ground speed over a day’s Sailin somewhere like the Solent,, and that 5 knots is a big difference on a polar diagram... Using ground wind simply would not work for that. With a 10 knot ground wind and 2 knots of tide against it I’m sailing in 12. But if I’m using GWS to reference my polars I think I’m a genius because I’m looking at the speed I should be doing in 10 kts and beating it. Then the tide changed and I still have 10 kts GWS but now only 8 knots TWS. Why can’t I do the same speed as before? I’ve got the same wind...
So we use TWS as it’s the measure of the power available to your sails.
GWS is interesting, but as a tool to predict what might happen next, not now.

Yes, that's probably why nobody in this thread and probably ever in the history of mankind has ever, ever suggested taking a load of performance metrics and then picking a situation where there's an additional performance factor to use them.

Apparent works fine though. Take a boat to a pond, sail it a X apparent wind on Y apparent point of sail and you can cheerfully go somewhere with 10 knots of tide and as long as the resultant apparent wind on the boat is still X and Y you'll go the same speed. So you can happily use that as a tuning target.

EDIT: Apparent works fine - apart from the point lw395 which is pretty conclusive AFAIC.

 

[Mark-1]

If you look at the polars for my dinghy, the bottom half of the chart would barely exist if the angles were apparent. We reach 45 degrees up from dead down wind, with the apparent wind well forward of the beam.

That's a very good point, thanks. Or Polars for a fast Cat or Windsurfer would only have one point of sail - close hauled everywhere (IYSWIM) [1], so that's pretty cast iron reason to use true relative to water.


So that pretty much wraps it up for me. I think I've got quite a lot out of this thread:

1) Answer to my usage question.
2) The knowledge that this issue has come up before and solutions have been proposed.
3) A good example where 'True Relative to Water Wind' is genuinely useful.

YBW, FTW.

[1] Probably exaggerating a bit.

 

[Richard10002]

If you had a flying rather than floating background then you would often have heard the term "surface wind" but never called ground wind. I'm with you in that True wind is as described in the Met. glossary. Any wind measured on something which is moving/drifting with tide is apparent wind.

Yes... I can see that surface wind would be a term when flying as they live in a 3D environment, where there can be different winds at different levels. To the extent that, at one spot on the earth, where you and I would call the wind True Wind, there could be a myriad of variances in the vertical plane.

 

[Uricanejack]

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?

Back in 84 there were no anemometers recognised as accurate enough by UK Meteorological Office. Wind was estimated from sea state.
The DOT 2nd Mate FGN. Didn't give a rats ass about sails.
Or it might just have been me.
Of course I thought it was all bollocks when they were trying to explain why they say Lee Ho or lee Oh? On the Tyne on a Saturday morning in December. After I had sept Friday night at the Shoreline.

I will just add you are all wrong.

The true wind is the wind caused by the Pressure Gradient.
Which due to Coriolis effect. blows along the Isobars. at 90 degrees to the pressure gradient(except for latitudes close to the equator)
Known as the Geostrophic wind.
The actual Meteorological Wind is the Geostrophic Wind.
The Observed Wind. Wind over water is slowed by friction at sea level and is no longer the true wind over the Earth. The wind is slowed by friction about 30 percent and Deflected Approx. 15 deg. towards the low at sea level.
Friction is greater over land.
The Observed wind over land is Slowed even more by friction Deflected approx. 30 deg towards the center of the low at sea level.

So the Ground Wind and the Sea Wind are different Neither of them is the true wind.

And I haven't even mentioned land and sea breezes yet

On my boat I use the "Observed Wind" which is the wind I see over the water. Which may or may not be moving.
And My Tell tales which give me my "apparent wind".

Buggered If I know what the true wind is most of the time. I don't have working wind instruments.
And If I did it would be at the top of the mast and different from the wind at sea level.

 

[Yealm]

Yes, it’s been a thing for about 10 years- as GPS has taken off as an integrated part of boat instruments.

Not me and, as I said earlier, I got 2nd Officer (Foreign Going), Certificate, in about 1983, a BSc in Nautical Studies a year later, and Yachtmaster in 2006. I have never considered True Wind to be anything other than what some are now calling Ground Wind, (a term I've never heard of before this thread), and it being anything different has not cropped up in any of my seagoing education.

So I have had a jib and a compass for about 45 of the 80 years you talk about.

It’s I have also never seen an instrument which referred to Ground Wind, True Wind and Apparent Wind and I wonder if it is a feature that has actually arisen in the past decade as I havent been to sea since 2010, and havent experienced any instruments newer than about 2007.

In another post someone suggests "you are out of date", to a previous poster so, perhaps, I am out of date, but only to the tune of ten years max..

 

[BelleSerene]

Apparent works fine though. Take a boat to a pond, sail it a X apparent wind on Y apparent point of sail and you can cheerfully go somewhere with 10 knots of tide and as long as the resultant apparent wind on the boat is still X and Y you'll go the same speed.

That’s an impressive river you’ve got running through your pond to give you ten knots of tide in it. I have failed to find ten knots at the top of the Alderney Race. Perhaps I should come training with you in your pond!

 

[Yealm]

Apparent Wind - combination of wind due to atmosphere, tide and boat motion.
True Wind - combination of wind due to atmosphere and tide.
Ground Wind - atmospheric wind alone.

This is what you get when you press the relevant button on your instruments !

 

[lw395]

Apparent Wind - combination of wind due to atmosphere, tide and boat motion.
True Wind - combination of wind due to atmosphere and tide.
Ground Wind - atmospheric wind alone.

This is what you get when you press the relevant button on your instruments !

Apparent wind: directly observed relative to the boat (with inevitable errors)
True wind: Apparent wind processed to remove boat speed vector (with more inevitable errors) Still relative to boat heading
True wind (compass) As above, processed to a compass bearing with more errors
Ground wind (indicated by bullpoo and guesswork or Ray Moron machine) as above munged with GPS estimate of boat speed vector.

Yer Actual Wind......
Has shifted while you've been reading this.

We had a couple of so-so races today, the telltales stuck to the jib in the rain and the 'real wind' coming down the valley at a snails pace was fighting with the 'proper wind' curving around the headland in fits and starts. There wasn't any sea breeze but we found some back wind bouncing off the cliffs.
What we think is the true wind doesn't matter nearly as much as what the kite feels.

On the whole, up to about lunchtime it was similar to XCWeather wind, but then switched to more like BBC wind.

 

[John the kiwi]

I think we all get that:
1 there is the wind velocity with respect to a fixed point on land.
2 there is a wind velocity w.r.t the water that you are floating in.
3 there is a wind velocity w.r.t to the boat you are on.
So we are having an argument about labels.
All agree that the last is apparent wind. (please don't let anyone seriously disagree with this.!)

Apparently(see what i did there?) the majority of users of wind information in the world, and according to the poll the majority of yachtsmen agree that the 1st of the above is called the True wind.
Leaves only 2 questions:
1. what do we agree to call the wind velocity w.r.t to the tide?
2. (and far more importantly,) why does the poll show 6754.42% vs 3735.58%?.
Doesn't add up to 100% even if you shift the decimal points.

 

[lw395]

...
2. (and far more importantly,) why does the poll show 6754.42% vs 3735.58%?.
Doesn't add up to 100% even if you shift the decimal points.

The percentages are obviously vectors.
We should be able to work out the angle between them, which either a lift or a header.

 

[Mark-1]

I think we all get that:
1 there is the wind velocity with respect to a fixed point on land.
2 there is a wind velocity w.r.t the water that you are floating in.
3 there is a wind velocity w.r.t to the boat you are on.
So we are having an argument about labels.
All agree that the last is apparent wind. (please don't let anyone seriously disagree with this.!)

This.

Anyone know how the RYA refers to the three values in their course literature? (I'm not saying that would be definitive, just curious, and suprised nobody has mentioned it so far.)

Personally, now I'm aware of the issue, I'm going to refer to refer to what I previously called 'true wind' (the wind blowing the smoke out of Fawley BFC/in the forecast/Chi Met) as ground wind. That's the only terminology change I need to make to avoid all future confusion.

One more thought: When laying an unbiased-as-possible start line I've always been anchored and never factor tide into Ground Wind, even on light wind days. I've never known anyone do it any other way[1]. Nobody has ever complained. Do committee boats really correct for tidal effect of the wind by adding the vector for 'tide wind' in at the anticipated start time? Can someone show me some evidence this has been happening? (Club OOD guidlines for instance.)

[1] Except some inland clubs where the start line is from from a fixed point on land making no attempt to avoid bias.

 

[GrahamD]

This.

Anyone know how the RYA refers to the three values in their course literature? (I'm not saying that would be definitive, just curious, and suprised nobody has mentioned it so far.)

Personally, now I'm aware of the issue, I'm going to refer to refer to what I previously called 'true wind' (the wind blowing the smoke out of Fawley BFC/in the forecast/Chi Met) as ground wind. That's the only terminology change I need to make to avoid all future confusion.

One more thought: When laying an unbiased-as-possible start line I've always been anchored and never factor tide into Ground Wind, even on light wind days. I've never known anyone do it any other way[1]. Nobody has ever complained. Do committee boats really correct for tidal effect of the wind by adding the vector for 'tide wind' in at the anticipated start time? Can someone show me some evidence this has been happening? (Club OOD guidlines for instance.)

[1] Except some inland clubs where the start line is from from a fixed point on land making no attempt to avoid bias.

You will find all you need to know about race management and tidal offset here

http://www.rya.org.uk/SiteCollectio... race official/Race Management Guide 2017.pdf, around pp. 35-39.

Ground wind and sailing wind are the favoured terms for the wind the committee boat experiences and that experienced by a boat drifting on the tide.

If you are RO at a major event and you do not take tide into account when setting a line you will get most of the fleet at one end of the line and consequent general recalls/ black flag starts. With club racing where numbers are smaller or competition less keen, it doesn't matter too much

 

[BelleSerene]

One more thought: When laying an unbiased-as-possible start line I've always been anchored and never factor tide into Ground Wind, even on light wind days. I've never known anyone do it any other way[1]. Nobody has ever complained. Do committee boats really correct for tidal effect of the wind by adding the vector for 'tide wind' in at the anticipated start time? Can someone show me some evidence this has been happening? (Club OOD guidlines for instance.)

With significant tide running across the start line, a good comedy boat will correct for it. After all, the boats feeling the 'true' (ie water) wind direction by reaching up and down the line won't care (and many won't know!) whether any bias they detect is due to the line not being set parallel to the ground wind, or due to a current flowing along the start line. So they'll bunch at one end, which it's the race officer's job to avoid. That's why a good race officer will make some attempt to correct for it.

But I have been aboard (we were using my boat) while a very experienced one didn't, and showed surprisingly little appreciation of it. His attitude was that it was best not to complicate things for the sailors - which failed to understand that this is only a complication for the committee boat; for the sailor, line bias is just whether the true (water) wind is square to the start line, whatever the cause.

Club Race Officer Course - RYA (click on the link): slides 14-16.

 

[Mark-1]

Can someone show me some evidence this has been happening? (Club OOD guidlines for instance.)

Club Race Officer Course - RYA (click on the link): slides 14-16.

Thanks, BS, that's conclusive, and if slide 14 is correct, the RYA refers to 'Water Wind' as 'Sailing Wind', which answers my other question.

 

[RichardS]

2. (and far more importantly,) why does the poll show 6754.42% vs 3735.58%?.
Doesn't add up to 100% even if you shift the decimal points.

Your computer is seriously frazzled.

Mine shows 64.49% correct and 35.51% incorrect.

Richard

 

[lw395]

This.

Anyone know how the RYA refers to the three values in their course literature? (I'm not saying that would be definitive, just curious, and suprised nobody has mentioned it so far.)

Personally, now I'm aware of the issue, I'm going to refer to refer to what I previously called 'true wind' (the wind blowing the smoke out of Fawley BFC/in the forecast/Chi Met) as ground wind. That's the only terminology change I need to make to avoid all future confusion.

One more thought: When laying an unbiased-as-possible start line I've always been anchored and never factor tide into Ground Wind, even on light wind days. I've never known anyone do it any other way[1]. Nobody has ever complained. Do committee boats really correct for tidal effect of the wind by adding the vector for 'tide wind' in at the anticipated start time? Can someone show me some evidence this has been happening? (Club OOD guidlines for instance.)

[1] Except some inland clubs where the start line is from from a fixed point on land making no attempt to avoid bias.

When we set a start line, particularly for dinghies, we are not too up ourselves to ask one of the competitors to beat across it and see how it looks.
If the wind is light and the tide is strong, I'd rather AP it than have half the fleet wrapped around the committee boat by a cross tide.

OTOH, I have sailed at championships where the RO has set lines where black flags are inevitable as the tide is sweeping people across the line, it's impossible to judge where the line is, and the fleet is full of pondbois who don't expect the tide to be so fierce.

When the tide is strongly along the line, if you want to make both ends of the line equally attractive, you need to move the down-tide end up wind. That may mean boats can only start on one tack, but they are equally well placed to get to the mark first. If you set a line square to the 'water wind', all the boats will queue up at the up-tide end.

You have to have a thick skin to be a good race officer.

 

[lw395]

With significant tide running across the start line, a good comedy boat will correct for it. After all, the boats feeling the 'true' (ie water) wind direction by reaching up and down the line won't care (and many won't know!) whether any bias they detect is due to the line not being set parallel to the ground wind, or due to a current flowing along the start line. So they'll bunch at one end, which it's the race officer's job to avoid. That's why a good race officer will make some attempt to correct for it.

But I have been aboard (we were using my boat) while a very experienced one didn't, and showed surprisingly little appreciation of it. His attitude was that it was best not to complicate things for the sailors - which failed to understand that this is only a complication for the committee boat; for the sailor, line bias is just whether the true (water) wind is square to the start line, whatever the cause.

Club Race Officer Course - RYA (click on the link): slides 14-16.

Slide 30 is where you want to look.
And it's interesting.
If you set the start to the sailing wind, competitors may be happy as they get the illusion of a fair start. It feels like a normal fair line in no tide.
It works when the tide is say 1 knot and the boats can do 5 knots on a beat.
The object of the race officer's life is to get the race away without damage, delay, protests etc. Not to give the muppets a fair start. That's a means to an end.

But re-draw it with 2 knots of tide and 4 knots of boat speed. Plot where a boat from each end would be after say three minutes, if one tacks, who will cross whom?