Judging true wind direction

[BlueSkyNick]

Seems to me that everybody understands the trigonometry, it is the terminology which is being debated.

When I did my Asst Race Office Course (ie to be a gopher without any responsibility), the term for which Flaming is describing True wind is .... Tide Induced Wind. Makes sense to me.

 

[The engineer]

not another term, at least it is self explanatory

 

[NealB]

Seems to me that everybody understands the trigonometry, it is the terminology which is being debated.

When I did my Asst Race Office Course (ie to be a gopher without any responsibility), the term for which Flaming is describing True wind is .... Tide Induced Wind. Makes sense to me.

Yes....I believe that is the term that Reeves-Fowkes uses in his excellent tidal stream book.

 

[webcraft]

Got it.

Sorry, but I believe Flaming has made up his own definition of true wind speed based on the name of a screen on his instrument display.

I suggest you take a look at Sailing USA's True and Apparent Wind calculators - you will see that they use actual speed as read on a GPS to calculate true and apparent wind, not speed through the water.

To calculate true wind you have to subtract ALL the non-wind motion vectors including that created by water movement (tide or current). These can in fact be resolved into one vector given by COG and SOG over the ground.

Flaming's take on this appears to be that the calculation of what he thinks of as 'true wind' uses only boat speed and direction through the water. He prefers to call what most of us think of as 'true wind' 'ground wind'.

Flaming's point is good and valid if it is intended to show that tidal vectors have to be taken into account when calculating true wind from apparent, but his attempt to redefine the term 'true wind' as distinct from what he calls 'ground wind' is not, IMO, helpful.

In the end it really doesn't matter. You could call it the 'actual' wind or the 'real' wind - as long as you understand that you have to subtract both powered and tidal vectors from apparent wind to arrive at the 'actual' wind the rest is just terminology.

As a teacher I prefer to keep it simple, and to stick to generally accepted definitions rather than making my own up - but you can think of it any way you want, so long as you understand that a change in the tidal vector will usually result in a change in the apparent wind affecting the boat.


- W

 

[webcraft]

Seems to me that everybody understands the trigonometry, it is the terminology which is being debated.

When I did my Asst Race Office Course (ie to be a gopher without any responsibility), the term for which Flaming is describing True wind is .... Tide Induced Wind. Makes sense to me.

Yep, that makes sense to me as well. Where Flaming is coming from is that the Raymarine screen that in fact shows tide-induced wind is labelled 'true wind'.

- W

 

[flaming]

I agree that this is how true wind speed on an instrument set up as you describe is calculated - indeed, I am just back from a 700 mile trip on a boat with a Raymarine system operating precisely as you describe. However, the instrument in that configuration is NOT measuring true wind speed as usually defined (unless there is no tidal or current vector). It is only an approximation of true wind speed. The value you refer to as 'ground wind speed' is what is normally called 'true wind speed'.

So - what is 'wrong' is your definition of true wind speed as the value measured by a boat instrument set up in a particular way. True wind was a concept understood and defined long before Seatalk was invented!

- W

But as with everything, once we start measuring and recording it we start to understand more, and with understanding comes refining of definitions.

It's the difference between the water speed and wind speed that actually makes our boat go - so that is the wind we need to know about in order to sail. It makes sense to me that this is called true wind, as now whenever I go out and the true wind is 10 knots I know what sails to put up, regardless of what components of wind and tide made that wind.

Knowing the ground wind is useful, as it will factor in what you expect to happen on tide changes, but in terms of the number you need to decide on which sail to hoist at the mark you're approaching - it's normally irrelavent.

 

[flaming]

Seems to me that everybody understands the trigonometry, it is the terminology which is being debated.

When I did my Asst Race Office Course (ie to be a gopher without any responsibility), the term for which Flaming is describing True wind is .... Tide Induced Wind. Makes sense to me.

To me the tide induced wind is the component of the true wind that is due to the tide.

I.e. if I'm drifting east at 3 knots in the tide, the tide induced wind is an easterly of 3 knots. Add this to the ground wind measured by the committee (anchored) boat's instruments to get the true wind that the sailors will actually sail in.

 

[Woodlouse]

Flaming isn't just making up terms on the spot. As he has said, for the last 30 or 40 years wind instruments have been calculating 'true' wind by measuring the apparent wind and speed from the anemometer and log. This obviously doesn't take into account drift from other sources such as tidal currents and so the wind it measures will not be what the wind is doing over the ground.

Since however for the last 40 years this has been accepted as 'true wind' for those with instruments there obviously needs to be another term brought into use now that GPS can be used to calculate the wind direction over the ground. The term that instrument makers have decided to use for this is 'ground wind'.

There's no point in getting upset about this. Definitions can and do change. The fact that the RYA doesn't teach this is probably an indication that the syllabus needs updating.

 

[The engineer]

I think it is evolution of technology that involves changing terms as time goes by. Just because that is how it is always been done it doesn't mean change is not an option. Reducing the headsail used to mean one thing, now it means something completely different

 

[The engineer]

Snap

 

[Deleted member 36384]

.... The term that instrument makers have decided to use for this is 'ground wind'.

There's no point in getting upset about this. Definitions can and do change. The fact that the RYA doesn't teach this is probably an indication that the syllabus needs updating.

For the leisure industry. It would appear to me the academics and professional organisations who measure wind have adopted a definition that is universally understood (despite being calculated wrongly as one of my links is concerned with).

The RYA syllabus is approved by the MCA today, which in turn inherited it from the DtP (or whatever it was), who compared the syllabus to the schemes used to train mariners for the merchant and Royal Navy, so that Britain would have small boat skippers who could be called up for appropriate maritime civil work in times of stress. So, the RYA does have a prerogative on this matter.

Raymarine, for example, have got the definitions wrong, simple.

 

[flaming]

Sorry, but I believe Flaming has made up his own definition of true wind speed based on the name of a screen on his instrument display. - W

Just to clarify where my definitions come from. I've been fortunate enough to train with some of our paralympic sailors, and these definitions were explained (probably far more clearly than I have) by their coach.

This was several years ago, and before I ever saw an option for ground wind on an instrument setup. They've been the convention in racing circles for many years.

 

[NealB]

The term that instrument makers have decided to use for this is 'ground wind'.

There's no point in getting upset about this. Definitions can and do change. The fact that the RYA doesn't teach this is probably an indication that the syllabus needs updating.

Hmmm....so some upstart instrument manufacturers come along and use a term that has been understood for generations, and is used to this day in most other walks of life to still have the 'old' meaning, but they claim it means somthing else.

Seems to me it would make more sense for the instrument manufacturers to have stuck with already existing usage.

Me...I ain't 'upset' as I only have the wind instruments I was born with, anyway!

 

[DaveS]

Flaming isn't just making up terms on the spot. As he has said, for the last 30 or 40 years wind instruments have been calculating 'true' wind by measuring the apparent wind and speed from the anemometer and log. This obviously doesn't take into account drift from other sources such as tidal currents and so the wind it measures will not be what the wind is doing over the ground.

Since however for the last 40 years this has been accepted as 'true wind' for those with instruments there obviously needs to be another term brought into use now that GPS can be used to calculate the wind direction over the ground. The term that instrument makers have decided to use for this is 'ground wind'.

There's no point in getting upset about this. Definitions can and do change. The fact that the RYA doesn't teach this is probably an indication that the syllabus needs updating.

I've followed this with interest, and I think we're now getting to the bottom of it. For a number of years fancier instruments have calculated a quantity they termed "true wind" using information derived solely from log and apparent wind data, and simply ignoring the error caused by water movement.

With GPS it's possible to do the calculation properly and derive true wind, but there's a problem - the term has already been (mis)used. A sensible course at this point would have been to declare that henceforth true wind can be correctly shown and, to avoid confusion, the previous falsely labelled true wind should be known as "water wind" or something. Instead, presumably to keep their customers comfortable, they would appear to have retained the false definition of "true wind" and invented a new term "ground wind" to mean the same as what the rest of the world, on and off the water, know as "true wind".

Brilliant!

 

[The engineer]

The reality is that because the big manufacturers have done it, it will become the norm and accepted terminology. In time syllabi and teaching will be changed to come in line with the real world.
As a yacht engineer I get examined by the MCA on checking flywheel bilges and removing turning gear when starting generators on small yachts. It is not relevant, but it takes time for things to evolve. The time is increased if people refuse to move with the times!

 

[webcraft]

Hmmm....so some upstart instrument manufacturers come along and use a term that has been understood for generations, and is used to this day in most other walks of life to still have the 'old' meaning, but they claim it means somthing else.

Seems to me it would make more sense for the instrument manufacturers to have stuck with already existing usage.

Me...I ain't 'upset' as I only have the wind instruments I was born with, anyway!

I don't think that is wholly fair . . . when it first became possible to integrate instruments the best approximation of true wind speed involved using boat speed and heading to calculate the vector to subtract form apparent wind. I don't think calling this 'true wind speed' was an attempt to redefine the term, I think it was just the closest approximation to TWS then available. When I was sailing last week the boat had old Seatalk instruments and it was obvious that it was using the mechanical log to calculate 'True Wind' speed and direction. I did understand however that it was not actually measuring truer wind, just an approximation that did not include any tidal vector. This was still helpful, if not 100% accurate.

What I DO find odd is (if this is in fact what is happening) is the apparent refusal of the instrument manufacturers to move with the technology and change the way the TWS figures are calculated so it is an accurate display of true wind. Instead they seem to prefer to use or invent a little-used term, 'ground wind', to create a third display that shows the real true wind speed while leaving available a display labelled 'true wind' that in fact shows tide induced wind.

I would like to sail with the ST70 instruments to see this in action. It may be helpful to Flaming, but it is going to confuse more people than it helps IMO, and seems rather unnecessary. The Merchant Navy use the term true wind, not ground wind, as do various oceanographic institutes.

- W

 

[NealB]

The reality is that because the big manufacturers have done it, it will become the norm and accepted terminology. In time syllabi and teaching will be changed to come in line with the real world.
As a yacht engineer I get examined by the MCA on checking flywheel bilges and removing turning gear when starting generators on small yachts. It is not relevant, but it takes time for things to evolve. The time is increased if people refuse to move with the times!

OK...maybe I am getting upset now, after all!

I hate people coming along and trying to 'bag' words as their own, whether it's '2012', or the word 'organic' (just means carbon-based, doesn't it?) or true wind!

And are sailors going to be the only people that come to use that rather peculiar definition?

 

[The engineer]

Then maybe it is the responsibility of instructors to inform and teach the confused about current technology that they will encounter.

 

[webcraft]

A sensible course at this point would have been to declare that henceforth true wind can be correctly shown and, to avoid confusion, the previous falsely labelled true wind should be known as "water wind" or something. Instead, presumably to keep their customers comfortable, they would appear to have retained the false definition of "true wind" and invented a new term "ground wind" to mean the same as what the rest of the world, on and off the water, know as "true wind".

Brilliant!

Nail on head. Considering the amount of confusion this thread seems to have generated I don't think Raymarine and Maretron are to be commended for this, and I for one hope that their b@stardised terminology does not 'catch on'

- W

 

[DaveS]

Then maybe it is the responsibility of instructors to inform and teach the confused about current technology that they will encounter.

Presumably including the fact that it is different terminology to that used by everyone else. That should definitely reduce confusion.