Terminology ........ Whats your Flavour?

[noelex 77]

Originally Posted by goboatingnow

Correct it's display a mathematical vector that's of little use to anyone outside of boat polar generation. In practice as has been done for centuries , such a measurement is approximated to the land TRUE Wind . Ie the sailor compares the reading with the expected forecast wind ( a very common usage of such info ) ignoring the small errors typically induced by current.

Dave

If there is little difference (I see you point, but don't quite agree. The thirty percent windspeed difference in my example indicates this) then ground wind is more preferable as the GPS derived speed tends to more accurate (on a cruising boat) than log based speed which is subject fouling.

Small speed differences can have a significant effect on true/ ground based wind calculations (especially the angle).

Rather than ground based wind as the default it is only possible to use true wind on most wind instruments. Which is historically based, but is silly in this day and age. Instrument makers should at least give us the option. Even those that prefer true could switch to ground wind if the paddlewheel becomes fouled.

BTW. For accurate polar generation true wind rather than ground wind is needed. Ground wind is irrelevant as far as the sails are concerned.

[Tantalus]

Originally Posted by noelex 77

If there is little difference (I see you point, but don't quite agree. The thirty percent windspeed difference in my example indicates this) then ground wind is more preferable as the GPS derived speed tends to more accurate (on a cruising boat) than log based speed which is subject fouling.

Small speed differences can have a significant effect on true/ ground based wind calculations (especially the angle).

Rather than ground based wind as the default it is only possible to use true wind on most wind instruments. Which is historically based, but is silly in this day and age. Instrument makers should at least give us the option. Even those that prefer true could switch to ground wind if the paddlewheel becomes fouled.

BTW. For accurate polar generation true wind rather than ground wind is needed. Ground wind is irrelevant as far as the sails are concerned.

It just occurred to me that, while there have been several sources cited establishing true wind as being relative to ground or true north, there have been no citations of literature regarding the contrary view that true is based on "water wind". Any citations please?

[StuM]

For those who say "true wind" is water referenced: when a boat is making leeway (being physically pushed sideways through the water by the wind), is the "water based true wind" actually referenced to the water or is it referenced to the boat?

[noelex 77]

Originally Posted by Tantalus

It just occurred to me that, while there have been several sources cited establishing true wind as being relative to ground or true north, there have been no citations of literature regarding the contrary view that true is based on "water wind". Any citations please?

Well we have some great experts on CF. So I will cite Dockhead who explained it very well:

Originally Posted by Dockhead

There is a long discussion about this in the archives.

Apparent Wind = the wind speed and direction in relation to your boat. So in a dead calm motoring ahead at 10 knots, you would have a 10 knot apparent wind at 0 degrees.

True Wind = the wind speed and direction in relation to the WATER. In the example above, you would have Apparent Wind of 10 knots and True Wind of 0. Your instruments calculate True Wind by taking Apparent Wind (the only thing your wind instruments measure directly) and taking out the vector for speed through the water. Which is why you get no true wind readout if you have not got STW data -- speed through the water data -- in your network.

Ground Wind = the wind in relation to land, not water. In the example above, if there is no current and no leeway, Ground Wind = True Wind. If you are motoring directly against a 5 knot current, however, then you have Apparent Wind of 10, True Wind of 0, and Ground Wind of 5. To calculate Ground Wind, your instruments take out the vector for SOG, rather than STW. Ground Wind is of no relevance to sailors unless we are sailing in a strong tidal current and are trying to anticipate what the wind will be like when the tide changes.


Before GPS, it was impossible to calculate Ground Wind. That is because the only speed data we had was STW. Possibly the idea of True Wind versus Ground Wind arose because instrument makers who suddenly had access to SOG data on the network needed some way to differentiate true wind calculated that way versus True Wind calculated using STW.

True Wind, as calculated with STW data, is actually what we really need, since our boats sail in the interface between water and air. If we were sailing in a 1000 knot current, we wouldn't give a damn that we have a 1020 knot true wind in the same direction. We would only feel or care about the 20 knots differential between the water and wind -- that's what we sail in. That is why no one bothered, I guess, to change the definition once instrument makers had access to SOG data.

This will be rather academic for anyone who sails in waters without strong currents. For them, SOG and STW, and therefore True Wind and Ground Wind, will be more or less the same most of the time, but for perhaps some effect of leeway. For others, like me, who sail in the English Channel where the tide rips at up to 10 knots (Alderney Race), the disinction is not academic.


Don't be confused by the fact that meteorologists use True Wind to describe the difference between wind and land. Of course they do -- they are sitting on land, not on water. That in no way contradicts our usage of True Wind as being the difference between wind and water.


You asked which kind of wind is expressed in relation to North, what kind of North, or your bow. Don't get confused by this. "True" in "True Wind" has nothing to do with True North. It means true as in -- without the effect of the boat's motion. Any wind can be expressed any way you want -- in relation to your bow, in relation to either kind of North. But your instruments will generally tell you wind in relation to your bow, which is what you need for sailing. Ground Wind, which you don't need for sailing -- which is irrelevant for sailing here and now (but may be relevant for planning), would be useful to know in relation to North, to the extent you care at all. Which North -- why that depends on how you think, and how your instruments are set up. I always use Magnetic for everything, so that is what I would want to know, personally.

I suppose you want an outside reference. So with a quick google search I came up with:
(I still think Dockheads explanation is better)

True Wind

[noelex 77]

Originally Posted by StuM

For those who say "true wind" is water referenced: when a boat is making leeway (being physically pushed sideways through the water by the wind), is the "water based true wind" actually referenced to the water or is it referenced to the boat?

We can reference wind three ways
Boat
Water
Land

With enough information we can work out all three. Which is why I don't understand what those three terms should be if make "true wind" land based.
We need three names not two.

If we correct for leeway it will only effect the first boat wind. Water and land wind are unaffected. However only sophisticated wind instruments correct for leeway most basic wind packages ignore the effect.

[Tantalus]

Originally Posted by noelex 77

Well we have some great experts on CF. So I will cite Dockhead who explained it very well:

I suppose you want an outside reference. So with a quick google search I came up with:
(I still think Dockheads explanation is better)

True Wind

Sorry, i wouldn't consider an article written by and for an instrument manufacturer a reliable source.

[noelex 77]

Originally Posted by Tantalus

Sorry, i wouldn't consider an article written by and for an instrument manufacturer a reliable source.

Is Dockhead an instrument manufacturer

Ok let's nail this down

I think everyone is agreed there is difference between apparent and some sort of "true wind" (at least I hope so)

So there remains two possibilities for the remaining reference points:

You believe water and ground based wind are the same
Or you believe there is difference. If it is the latter what do we call these two different referenced winds?

You are obviously unhappy with "true" and "ground" but you must recognise, we need to have different terms to separate them and avoid confusion.

What do we call these two alternatives?

"True" and "ground" are really silly, poorly named terms terms, so I am happy for alternative names (if we can get it widely adopted), but we at least need suggestions rather than pretending that they are both the same because the nomenclature is clumsy.

[Jammer Six]

Originally Posted by goboatingnow

It's may be so in military communications , but it has no place in marine VHF parlance

If you say so.

If you call "mayday", you will be answered by the U.S. Coast Guard, which is one of five military organizations.

Why do you think military SOP has no place in marine communications, since a lot of marine communication IS military?

I notice you've been asked for a citation, and I'll add my request to that list: please its your source.

[Hoofsmit]

Originally Posted by larryklaas

Leeway is the lateral slippage of a vessel caused by a variety of factors including press of sail, wave action, current, and/or "prop walk." It is expressed in degrees left or right of dead ahead. May I suggest you consult an excellent reference: The Encyclopedia of Nautical Knowledge.

Thanks but I should have made it clearer

1. I agree in a forecast ,
but what about an electronic wind indicator

2. Then follows

Ps the mods will have you for the coloured txt

[Lee Jerry]

Originally Posted by noelex 77

Is Dockhead an instrument manufacturer

Ok let's nail this down

I think everyone is agreed there is difference between apparent and some sort of "true wind" (at least I hope so)

So there remains two possibilities for the remaining reference points:

You believe water and ground based wind are the same
Or you believe there is difference. If it is the latter what do we call these two different referenced winds?

You are obviously unhappy with "true" and "ground" but you must recognise, we need to have different terms to separate them and avoid confusion.

What do we call these two alternatives?

"True" and "ground" are really silly, poorly named terms terms, so I am happy for alternative names (if we can get it widely adopted), but we at least need suggestions rather than pretending that they are both the same because the nomenclature is clumsy.

I have seen the term "sailing wind" used as the combination of the ground wind plus current induced wind (i.e. the wind that the boat sees without it's own contribution).

Thus the three types could be:
Ground
Sailing = ground + current induced wind
Apparent = sailing + boat motion induced

(PS - for me, sailing wind = true wind)

[Hudson Force]

I am intrigued by this ambiguity. I'll waste no time in reading more!

[a64pilot]

Originally Posted by CaptForce

I am intrigued by this ambiguity. I'll waste no time in reading more!

Is that a Monty Python qoute?

[SV Sea Monkey]

Originally Posted by goboatingnow

It's may be so in military communications , but it has no place in marine VHF parlance Dave

Don't tell the Navy.

[Paul Elliott]

[re: Saying "BREAK"]

Originally Posted by goboatingnow

It's may be so in military communications , but it has no place in marine VHF parlance

Dave

Why on earth would you say that? Especially with VHF FM, the proper use of "BREAK" is very appropriate during a long-winded informational broadcast on a distress and hailing channel.

Even on SSB, I think it can be appropriate. During the last three Pacific Cup races (San Francisco to Hawaii) I have been the communications boat. As part of my duties I have to read over the air long lists of boats and their positions. My duties also include monitoring the channel for emergency traffic during our net times. I use BREAK regularly so I can listen for emergency traffic during my broadcasts. And yes, I have received semi-emergency traffic during these nets. Example: a keel fell of a boat returning from the singlehanded transpac race. They contacted me during one of our scheduled Pacific Cup radio nets.

[Dockhead]

Originally Posted by noelex 77

If there is little difference (I see you point, but don't quite agree. The thirty percent windspeed difference in my example indicates this) then ground wind is more preferable as the GPS derived speed tends to more accurate (on a cruising boat) than log based speed which is subject fouling.

Small speed differences can have a significant effect on true/ ground based wind calculations (especially the angle).

Rather than ground based wind as the default it is only possible to use true wind on most wind instruments. Which is historically based, but is silly in this day and age. Instrument makers should at least give us the option. Even those that prefer true could switch to ground wind if the paddlewheel becomes fouled.

BTW. For accurate polar generation true wind rather than ground wind is needed. Ground wind is irrelevant as far as the sails are concerned.

I agree with both of you. I think Dave meant that no one bothered to think much about the distinction so long as there was no accurate way to measure.

As to options, I think the instrument makers have it right. Give us ground wind only in relation to a compass rose; useless and potentially confusing in relation to bow.true wind in relation to bow only water-referenced.