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Old 29-12-2012, 17:37   #16
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Re: Acronym TWS and TWD ?

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Originally Posted by noelex 77 View Post
If Program's can be written to incorporate ground based wind (using SOG) I think quite a few cruising sailors will prefer this option when they have tried it.
NavMonPc has a "water/ground reference" option. Sometimes the boat has windspeed instruments, but no water-speed, so there's no choice but to use the GPS-provided SOG and ground-referenced wind calculations. Other times, it just the user's preference. It's easy enough to do the calculations, and I'm sure that OpenCPN could provide it with very little effort.

And we haven't even discussed the effects of leeway in the True / Apparent calculations! It gets complicated to do this stuff well. NavMonPc does an "adequate" job of it.
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Old 29-12-2012, 17:48   #17
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Irrespective of how's its computed True Wind as has been understood by sailors is water referenced wind. It's has uses in polars and sail trim, its is calculated using HDG and STW ( to use the NMEA designators ) ground wind is the wind as experience at anchor or the forecast and if earth referenced and calculated using SOG and COG.

In practice in the open sea there is little difference.

Dave
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Old 29-12-2012, 21:36   #18
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Re: Acronym TWS and TWD ?

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Originally Posted by Vasco View Post
Technically speaking you're out in left field. They certainly are acronyms.
Well they aren't anagrams. An anagram is a new word formed by rearranging the letters of another word. Like brain becomes Brian or stain becomes satin.

Strictly speaking an acronym is a word formed by the first letters of something like SCUBA or RADAR. However if you don't say it as a word but just say the letters like IBM or PFD then technically that would be an initialism.

But obviously I am now seriously nit picking, a risk of posting late on Saturday night.
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Old 29-12-2012, 21:42   #19
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Re: Acronym TWS and TWD ?

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Everyone keeps looking at and configuring this open cpn software and I don't know why it is so much in demand. I understand and respect everyone's choices here but not the attraction.
Well it is nice for us lucky sailors over here in the colonies because we can download all the US charts free. Add a nice, fully functional, free nav program to free charts and there's the attraction.



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I use is os device with navionics marine app. It costs very little indeed and permits me endless and free downloads for every chart possible.

I can't fault it especially considering the cost
Sorry, I'm a bit confused (easy to do). I think you are referring to Apple products like iPads, etc? I seem to recall that with nav apps on an iPad do you get cheap charts.
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Old 30-12-2012, 12:54   #20
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Re: Acronym TWS and TWD ?

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Irrespective of how's its computed True Wind as has been understood by sailors is water referenced wind. It's has uses in polars and sail trim, its is calculated using HDG and STW ( to use the NMEA designators ) ground wind is the wind as experience at anchor or the forecast and if earth referenced and calculated using SOG and COG.

In practice in the open sea there is little difference.

Dave
How else could True Wind be referenced other than to water? What do we know about the ground, out at sea? The relative motion between wind and sea is what powers us - of course that is the True Wind we care about.
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Old 30-12-2012, 18:06   #21
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Originally Posted by Dockhead

How else could True Wind be referenced other than to water? What do we know about the ground, out at sea? The relative motion between wind and sea is what powers us - of course that is the True Wind we care about.
Well with s we can now calculate ground wind.
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Old 31-12-2012, 02:26   #22
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Re: Acronym TWS and TWD ?

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In practice in the open sea there is little difference.

Dave
That's true in theory. If there is no current their is no difference (in theory)

In practice there tends to be a big difference.

Most cruising boats have poorly calibrated logs. They very often read a bit different on different tacks, upwind and down. Even if they start out OK a few months at anchor sees some growth on the transducer or on the hull that disturbs the water flow and the calibration becomes inaccurate.
Yes you can pull the transducer and clean it, or dive and also clean the hull around the transducer, which is better, but few cruising boats bother until the readings become poor.

GPS the advantage that its always in perfect calibration. It does suffer some random speed errors, and the update rate it is a little lower, but in my experience it provides better wind information than using the log on a cruising boat.

Modern GPS units are much better,a sat differentional signal makes a huge difference, and you want to use it this way get one of the 5hz models when the GPS needs replacement.

For a race boat the situation is reversed. They will typically place the log in the optimum position, keep the log and bottom spotless clean and of course recalibrate the log regularly.
Assuming both are equally acurate, true wind is also probably a more useful number for a racing sailor where ground wind is useful for a cruising sailor.

The ultrasonic logs should solve some of these problems, but at the moment they expensive and have been a little unreliable.

If you are a cruising boat give ground wind a try.
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Old 31-12-2012, 05:18   #23
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Oh I agree fully and my true wind systems all use SOG. I was merely drawing attention to the fact that TWS is by definition in the marine world water referenced no ground referenced.

Dave
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Old 31-12-2012, 07:56   #24
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Re: Acronym TWS and TWD ?

Parts of this was discussed a looong time ago and I wrote some text and made a sketch. It may be still be of use to show the different terms even if the start of that discussion related to WCV and VMG (described in the discussion).

/Jonas
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Old 01-01-2013, 10:37   #25
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Re: Acronym TWS and TWD ?

Simple question...lots of disussion and understanding.
Just for cross reference, in this thread there is more discussion
Thread: PCSail - Excel sheet to make VPP for Sailing yachts
Specifically:
1. Paul Elliot Post

Long Thread: Integration with QtVlm - Data files and Import/Export

1. rgleason - Summary of Boat, Wind, Current, WP Data
2. Maitai - Differences between Wind on water, Wind on ground calcs.
3. Maitai - Further explanation.
4. rgleason & maitai following - TW ground relative vx TW water relative & calculation
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Old 02-01-2013, 04:01   #26
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Re: Acronym TWS and TWD ?

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Technically speaking you're out in left field. They certainly are acronyms.
No, poster LeonJennings is correct and you're the one "out in left field" They most certainly are not acronyms; the letters do not form a real word in common usage, which they must do to count as an acronym.
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Old 02-01-2013, 06:20   #27
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Re: Acronym TWS and TWD ?

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No, poster LeonJennings is correct and you're the one "out in left field" They most certainly are not acronyms; the letters do not form a real word in common usage, which they must do to count as an acronym.
I think we're wading way off topic...

But as I understand it there is no universal aclaim to that acronyms have to be "words".
The definitions are for sure not anagrams which are words that read the same when read from left to righ to as well as from righ to left.
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Old 02-01-2013, 07:07   #28
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Re: Acronym TWS and TWD ?

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I think we're wading way off topic...

But as I understand it there is no universal aclaim to that acronyms have to be "words".
The definitions are for sure not anagrams which are words that read the same when read from left to righ to as well as from righ to left.
It's you who's off-topic. A word reading the same L-R or R-L is a palindrome. An anagram is a word whose letters are scrambled to make another word or words.
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Old 02-01-2013, 07:10   #29
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Re: Acronym TWS and TWD ?

ac·ro·nym noun \ˈa-krə-ˌnim\
-Off topic Acronym - Definition and More from the Free Merriam-Webster Dictionary

Definition of ACRONYM
: a word (as NATO, radar, or laser) formed from the initial letter or letters of each of the successive parts or major parts of a compound term; also : an abbreviation (as FBI) formed from initial letters : initialism

Examples of ACRONYM
The North Atlantic Treaty Organization is known by the acronym “NATO.”

Origin of ACRONYM
acr- + -onymFirst Known Use: 1943
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Old 02-01-2013, 07:42   #30
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Re: Acronym TWS and TWD ?

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...palindrome...
Ooops. Of course. You're right. My wrong.
We are of course all of topic regarding the original subject.
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