Lee bowing

[TLouth7]

I would call it calculated or relative or sailing.

I dislike the first two because "calculated" implies that it is not a real thing, and "relative" would confuse things even more. Sailing Wind on the other hand does actually describe the phenomenon, and what it is useful for. A pity it doesn't appear on any instruments though...

If that were true they would all have to have exactly the same drag. Which would require them to have exactly the same crossectional area and Cd.

I think you are not seeing where this Sailing Wind comes from. It is simply:

Ground Wind - Tidal Stream = Sailing Wind

and/or

Apparent Wind + Velocity through Water = Sailing Wind

so can be calculated either by a tactician with weather data and tidal stream atlas or by an instrument with heading, log (STW), AWA and AWS readings. These calculations will be imperfect for real vessels but that does not mean that there is not a single correct Sailing Wind at any given point in time and space.

 

[dom]

If that were true they would all have to have exactly the same drag. Which would require them to have exactly the same crossectional area and Cd.

They don’t.

You are describing spherical boats of zero mass in a vacuum.

Drag?? Suspect you're just trolling now

 

[Buck Turgidson]

Drag?? Suspect you're just trolling now

Well let me ask this. If you put 5 vessels of dissimilar type in a tidal flow and let the drift will the drift at the same speed? All facing the same heading?

 

[dom]

Well let me ask this. If you put 5 vessels of dissimilar type in a tidal flow and let the drift will the drift at the same speed? All facing the same heading?

If there is no wind, then yes. They will move at exactly the same speed and in exactly the same direction with respect to the land, but adopt entirely random headings.

 

[flaming]

Well let me ask this. If you put 5 vessels of dissimilar type in a tidal flow and let the drift will the drift at the same speed? All facing the same heading?

If there is no wind, and it's just tidal flow then the difference you are talking about is the drag on the boat of a wind equal to the tidal flow. So say 3 knots. How fast does any boat drift in still water and a 3 knot wind?
The difference between the boats would be well within the margin of error of your GPS, let alone your log.

 

[flaming]

If there is no wind, then yes. They will move at exactly the same speed and in exactly the same direction with respect to the land, but adopt entirely random headings.

Not quite, as they will be subject to the drag of the wind induced by the tide. But that wind will be small, so the differences will be tiny.

 

[dom]

Not quite, as they will be subject to the drag of the wind induced by the tide. But that wind will be small, so the differences will be tiny.

Indeed, which is why to try and keep this tight I defined TWS as measured from a vessel 'stationary' with respect to its inertial frame of reference, i.e. the tidal stream in this case.

Otherwise someone might argue that the TWS as measured from the perspective of an empty plastic Coke bottle skittering around on a pond, would be different to that measured from a half sunken barge :ambivalence:

 

[TLouth7]

If there is no wind relative to the moving water (Sailing Wind/True Wind) then all the boats will drift along at precisely the speed of the current.

 

[Buck Turgidson]

Indeed, which is why to try and keep this tight I defined TWS as measured from a vessel 'stationary' with respect to its inertial frame of reference, i.e. the tidal stream in this case.

Otherwise someone might argue that the TWS as measured from the perspective of an empty plastic Coke bottle skittering around on a pond, would be different to that measured from a half sunken barge :ambivalence:

And they would be correct which is why there is nothing true about it. And industries that require True wind all use the earth frame.

 

[Buck Turgidson]

If there is no wind relative to the moving water (Sailing Wind/True Wind) then all the boats will drift along at precisely the speed of the current.

Is not correct!

https://www.terrapub.co.jp/onlineproceedings/ec/05/pdf/PR_05239.pdf

 

[TLouth7]

If there is no wind relative to the moving water (Sailing Wind/True Wind) then all the boats will drift along at precisely the speed of the current.

Is not correct!

Then we will have to agree to disagree because this is absolutely correct.

Consider: what force acts on the boat to move it at a different speed to the water?

 

[Buck Turgidson]

Then we will have to agree to disagree because this is absolutely correct.

Consider: what force acts on the boat to move it at a different speed to the water?

Read the document I attached to my last post in the edit.

 

[Daydream believer]

All these comments about true wind & ground wind & the effect of tide on the wind direction; but no one has mentioned the Coriolis effect yet. Nor have they mentioned the effect that it has on tacking angle when talking about pinching, which possibly leads us to twist.
The Coriolis effect can be quite marked at even quite low levels.
I did find this
http://www.ockam.com/2013/06/02/wind-shear/

 

[dom]

And they would be correct which is why there is nothing true about it. And industries that require True wind all use the earth frame.

And that's great: the International Astronomical Union has chosen the ICRS (International Celestial Reference System), the UK Admiralty the World Geodetic System 1984, etc.

The major electronic OEMs by comparison have adopted the terminology used by sailors all around the world, which is what I and some others have tried to describe.

If you want to use a non-standard language, that's just fine. No point in arguing who is right, anymore than it is worth arguing whether it's better to be German or English. That said, someone has to translate, or someone has to learn the other's language if they wish to communicate. Simples

 

[dom]

All these comments about true wind & ground wind & the effect of tide on the wind direction; but no one has mentioned the Coriolis effect yet. Nor have they mentioned the effect that it has on tacking angle when talking about pinching, which possibly leads us to twist.
The Coriolis effect can be quite marked at even quite low levels.
I did find this
http://www.ockam.com/2013/06/02/wind-shear/

It's kind of true, but you'd need NASA instruments to measure it and I mean the Cape Canaveral variety!

In practice, people who refer to Coriolis lifting on one tack are talking through their hats
Wind gradient is by comparison a very real and important concept.

No doubt someone will be along soon to strongly disagree :ambivalence:

 

[RupertW]

And that's great: the International Astronomical Union has chosen the ICRS (International Celestial Reference System), the UK Admiralty the World Geodetic System 1984, etc.

The major electronic OEMs by comparison have adopted the terminology used by sailors all around the world, which is what I and some others have tried to describe.

If you want to use a non-standard language, that's just fine. No point in arguing who is right, anymore than it is worth arguing whether it's better to be German or English. That said, someone has to translate, or someone has to learn the other's language if they wish to communicate. Simples

I think you’ve got this the wrong way round, some sailors around the world have adopted the OEMs over-simplified version of True Wind, and now think the inaccuracy is actually the new definition. Plenty of sailors do think that, but it doesn’t make it right and it certainly isn’t helpful to all the other sailors who actually understand what their instruments can, and can’t do.

 

[Buck Turgidson]

I think you’ve got this the wrong way round, some sailors around the world have adopted the OEMs over-simplified version of True Wind, and now think the inaccuracy is actually the new definition. Plenty of sailors do think that, but it doesn’t make it right and it certainly isn’t helpful to all the other sailors who actually understand what their instruments can, and can’t do.

I concur.

 

[flaming]

Read the document I attached to my last post in the edit.

Unless I'm misreading that document, it is talking about windspeed acting on the object. In the situation where you have no difference in velocity between the air and water, then all boats will move the same.

When you are discussing the effect of the tide on a boat you have to remember that the equal and opposite "wind" that is created by moving the boat through the air on the tide is created in a fluid that is nearly 800 times less dense than the water of the tide. And therefore the force due to that component of the wind is negligible compared to the force of the tide on the boat - so to all practical purposes all boats do drift equally on the tide.

Where you also have strong winds, then obviously this will then result in heavy long keeled boats drifting differently from lightweight race boats, but that is due to the movement of the boat through the water due to strong winds - and not the movement of the water in which the boat is floating. The same relative movement between the boats would be found with a strong wind equal to the vectors of the ground wind and tidally produced wind acting on the boats on a pond or lake.

 

[flaming]

I think you’ve got this the wrong way round, some sailors around the world have adopted the OEMs over-simplified version of True Wind, and now think the inaccuracy is actually the new definition. Plenty of sailors do think that, but it doesn’t make it right and it certainly isn’t helpful to all the other sailors who actually understand what their instruments can, and can’t do.

I agree, to an extent. But in the sphere of sailing it is not helpful to use the phrase "true wind" unless you are referring to what is measured by the OEM's kit and displayed as "True Wind". Otherwise you basically have to have this conversation every time you mention it....

I also don't actually see any problems or logical difficulties with the True wind as used by sailors differing from that used by pilots for example. It is clear that each user is going to be interested in the wind relative to their reference point. For pilots that's the earth, for sailors the sea.

 

[TLouth7]

Read the document I attached to my last post in the edit.

I have and I can't see anything to refute my claim that boats which are floating in a stream and experiencing no Sailing Wind will move precisely with the current. Could you summarise how the linked article disputes that?

I accept that different vessels drift at different speeds through the water when they experience a wind, but that drift appears twice the calculation for Sailing Wind (as a component of Apparent Wind and as the boat's Velocity through Water) so it cancels out. Remember the calculation is:

Apparent Wind + Velocity through Water = Sailing Wind