Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 27-05-2011, 10:24   #136
Registered User
 
Tempest245's Avatar

Join Date: May 2008
Location: Piscataway, NJ
Boat: 34 Sabre Tempest
Posts: 937
Re: What Heading Am I Really On ?

In the example above... I believe the True wind on land is 2 knots....not 18 knots

Current reverses...apparent wind is 7 knots...5 knots of TTW, 2 knots of true wind..

I assume..you're motoring..;-) I can't do 5 knots in 2 knots of wind.

I don't recognize the term " ground wind" as relevant to what we do as sailors.
We sail the "apparent wind."

From what I have read, the electronics manufactures ( maretron being one of them)
have tried to devise a calculation to determine what the true wind would be taking into consideration the current and apparent wind. Their reason for doing this is so that a mariner can determine where weather might be coming from.
__________________

__________________
Tempest
Tempest245 is offline   Reply With Quote
Old 27-05-2011, 10:33   #137
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
2 knots of true ??? Show the math
Dave

What I'm trying to show is that " true wind " as calculated using STW is a merely a mathematical computation and in fact has no real component.
__________________

__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 27-05-2011, 10:35   #138
Registered User
 
wolfaroo's Avatar

Join Date: Mar 2010
Location: UK South Coast
Boat: Unknown MFV 60ft
Posts: 111
Re: What Heading Am I Really On ?

Quote:
Originally Posted by goboatingnow View Post
What's the ground wind calculation ? Also redo your calculation as true is computed using only boat speed through the water.

And sorry yes SoG falls to 2 knots.
With SOG at 2 knots...

Boat speed STW = 5 knots
Apparent wind = 16 knots
True wind = 18 knots

If this is right do I win a beer/wine/rum?

Ground wind: I think simply that some people use this term and some don't - you can see from my previous posts and the above calculation that my 'true' wind is probably the same as your 'ground' wind. I have never used the term before and I consider tide-induced wind to be a component of apparent wind.

Having said that, I do understand that true wind can be referenced to the land or the sea. I guess I was always taught that true wind is the wind experienced when not underway (e.g. at anchor) and everything else is apparent.

Maybe when I can afford new instruments I will start using the term ground wind!
__________________
"It is good to have an end to journey towards; but it is the journey that matters in the end."
Ursula Le Guin
wolfaroo is offline   Reply With Quote
Old 27-05-2011, 10:46   #139
Registered User
 
Tempest245's Avatar

Join Date: May 2008
Location: Piscataway, NJ
Boat: 34 Sabre Tempest
Posts: 937
Re: What Heading Am I Really On ?

Quote:
Originally Posted by goboatingnow View Post
2 knots of true ??? Show the math
Dave

What I'm trying to show is that " true wind " as calculated using STW is a merely a mathematical computation and in fact has no real component.
Oops, sorry, I missed the 1st sentence...where you stated you were sailing WITH the wind.......so I agree with the others..18 knots of true on land.
__________________
Tempest
Tempest245 is offline   Reply With Quote
Old 27-05-2011, 11:19   #140
Registered User
 
HappySeagull's Avatar

Join Date: Dec 2010
Location: B.C.,Canada
Boat: 29'
Posts: 2,395
Re: What Heading Am I Really On ?

...the sailboat has effective airbrakes and current affects it less in this instance
__________________
HappySeagull is offline   Reply With Quote
Old 27-05-2011, 11:22   #141
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Ok let's simplify it
Let's take a motor boat so that we can remove the relationship between boat speed and apparent.

Hence current with us

True is 15
Ground is 18

Current reverses

Apparent increases to 16 (due to current)
Sog is 2

True increase to 21 (apparent + stw)

Ground is 16 + 2 = 18 ( app + Sog) which is consistent.

However it shows the nonsense of calculated true from STW
Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 27-05-2011, 11:34   #142
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2006
Location: Chesapeake Region and Maine
Boat: 42' Bob Perry sloop
Posts: 4,038
Images: 4
Re: What Heading Am I Really On ?

Quote:
Originally Posted by wolfaroo View Post
................

Having said that, I do understand that true wind can be referenced to the land or the sea. ............

NO, NO, NO!

There is only one true wind. It is the wind referenced to a single geographic point (whether on land or the sea bottom...doesn't matter), and is generally stated as degrees clockwise from TRUE NORTH.

See, e.g., NOAA definition and virtually all other authoritative definitions on record.

TRUE WIND has been so defined for hundreds of years.

TRUE WIND has absolutely nothing to do with boat movement. It is what it is, no matter what the boat is doing.

Wind caused by boat movement, whether tide or current or leeway or motor or sails, when vectored together with TRUE WIND is the APPARENT WIND.

If the boat is at the dock, then the TRUE WIND is the same as the APPARENT WIND.

All these other "definitions" or "spins" on True Wind were dreamed up by computerniks and equipment manufacturers, trying to cram new features into their equipment.

Why make it more complicated than it is?

Bill
__________________
btrayfors is offline   Reply With Quote
Old 27-05-2011, 11:47   #143
Registered User
 
wolfaroo's Avatar

Join Date: Mar 2010
Location: UK South Coast
Boat: Unknown MFV 60ft
Posts: 111
What Thread Am I Really On ?

Quote:
Originally Posted by goboatingnow View Post
However it shows the nonsense of calculated true from STW
Dave
No it shows the nonsense of GROUND wind replacing the true TRUE wind

Well it is Friday

btw Jim, I really enjoyed your post, thanks. For me one of the great things about sailing is it can be as complex as you choose to make it. Whilst I might plan one passage in great detail the night before, I may well sail another without considering much other than are there enough chilled beers .

Did someone mention beer?
__________________
"It is good to have an end to journey towards; but it is the journey that matters in the end."
Ursula Le Guin
wolfaroo is offline   Reply With Quote
Old 27-05-2011, 11:54   #144
Registered User
 
wolfaroo's Avatar

Join Date: Mar 2010
Location: UK South Coast
Boat: Unknown MFV 60ft
Posts: 111
Re: What Heading Am I Really On ?

Quote:
Originally Posted by btrayfors View Post
NO, NO, NO!

There is only one true wind. It is the wind referenced to a single geographic point (whether on land or the sea bottom...doesn't matter), and is generally stated as degrees clockwise from TRUE NORTH.

See, e.g., NOAA definition and virtually all other authoritative definitions on record.

TRUE WIND has been so defined for hundreds of years.

TRUE WIND has absolutely nothing to do with boat movement. It is what it is, no matter what the boat is doing.

Wind caused by boat movement, whether tide or current or leeway or motor or sails, when vectored together with TRUE WIND is the APPARENT WIND.

If the boat is at the dock, then the TRUE WIND is the same as the APPARENT WIND.

All these other "definitions" or "spins" on True Wind were dreamed up by computerniks and equipment manufacturers, trying to cram new features into their equipment.

Why make it more complicated than it is?

Bill
Bill I agree and this is basically what I have been saying in all my previous posts, but there seems to be a number of 'ground wind' folk on this forum and I guess I was trying not to upset them all when I left the true wind backdoor slightly ajar!!!
__________________
"It is good to have an end to journey towards; but it is the journey that matters in the end."
Ursula Le Guin
wolfaroo is offline   Reply With Quote
Old 27-05-2011, 12:17   #145
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Wolfaroo your hilarious you've just contradicted yourself.

Because you're against ground wing replacing true in boat instruments while agreeing with bill who argued that ground wind is actually true wind.

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 27-05-2011, 12:21   #146
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 3,866
Images: 4
Re: What Heading Am I Really On ?

Quote:
Originally Posted by btrayfors View Post
NO, NO, NO!

There is only one true wind. It is the wind referenced to a single geographic point (whether on land or the sea bottom...doesn't matter), and is generally stated as degrees clockwise from TRUE NORTH.

See, e.g., NOAA definition and virtually all other authoritative definitions on record.

TRUE WIND has been so defined for hundreds of years.

TRUE WIND has absolutely nothing to do with boat movement. It is what it is, no matter what the boat is doing.

Wind caused by boat movement, whether tide or current or leeway or motor or sails, when vectored together with TRUE WIND is the APPARENT WIND.

If the boat is at the dock, then the TRUE WIND is the same as the APPARENT WIND.

All these other "definitions" or "spins" on True Wind were dreamed up by computerniks and equipment manufacturers, trying to cram new features into their equipment.

Why make it more complicated than it is?

Bill
Bill, I'm going to respectfully disagree with you.

There is a huge difference between True Wind Direction (ground-referenced) and True Wind Angle (traditionally water-referenced). Here's how I understand the terms:

Apparent Wind Angle and Speed (AWA, AWS): This is wind relative to the boat, as seen by the masthead wind instruments. Boat speed, leeway, current, etc, are not factored into AW measurements. I think we are all in agreement regarding Apparent Wind.

True Wind Angle and Speed (TWA, TWS): Traditionally, this takes Apparent Wind, and corrects it for boat speed through the water using simple vector math. Current is not used in this calculation, TWA and TWS are relative to the water.

True Wind Direction is referenced to the ground, and has nothing to do with the boat's speed or direction, except that these are needed if you want to calculate TWD from the AW measurements taken from a moving boat. Calculating TWD is usually done with AW, SOG, COG, and heading.

TWS has become an ambiguous term, as it can refer to either the traditional TWS (water-referenced), or the ground-referenced wind used for TWD. Unless obvious from context or otherwise specified, when talking about sailboats I assume TWS is water-referenced.

These concepts are simple enough, where we might disagree is in the definition of some of the terms. The introduction of GPS, giving us easy access to COG and SOG, has confused the traditional meanings of True Wind.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is online now   Reply With Quote
Old 27-05-2011, 12:22   #147
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
This is the kernel. For years mariners calculated true wind using STW which produces a computation that is in fact meaningless . Mariners called this true wind everyone else regards " ground wind " ie wind speed and direction referenced to the earth as " true wind"


Ground wind was named by electronics companies to get around the computational nonsense that is " marine true wind"

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 27-05-2011, 12:32   #148
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Quote:
Originally Posted by Paul Elliott

Bill, I'm going to respectfully disagree with you.

There is a huge difference between True Wind Direction (ground-referenced) and True Wind Angle (traditionally water-referenced). Here's how I understand the terms:

Apparent Wind Angle and Speed (AWA, AWS): This is wind relative to the boat, as seen by the masthead wind instruments. Boat speed, leeway, current, etc, are not factored into AW measurements. I think we are all in agreement regarding Apparent Wind.



Sorry nonsense apparent wind combines all factors Leeway, tide weight anything that effects the boat. It's a real life value


Btw taking about " angles " is misleading that's merely because we have normally only " relative " angles on a boat. It's easy now to produce absolute angles TWA is the same as True wind direction.

The fact is mariners true wind is nothing of the sort it's based on a calculation that uses STW to approximate what actually is wanted which is landlubbers " true wind"

Now that we can actually calculate it we are trying to justify the existence of that misformed value.

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 27-05-2011, 13:09   #149
Registered User
 
wolfaroo's Avatar

Join Date: Mar 2010
Location: UK South Coast
Boat: Unknown MFV 60ft
Posts: 111
Re: What Heading Am I Really On ?

Quote:
Originally Posted by goboatingnow View Post
Wolfaroo your hilarious you've just contradicted yourself.

Because you're against ground wing replacing true in boat instruments while agreeing with bill who argued that ground wind is actually true wind.

Dave
Contradicted myself, shot myself in the foot or got shot in the foot?

I know . I made several posts and in ALL of them I stated that I either don't agree with the term 'ground wind' and that what I think of as true wind is what some others appear to think of as ground wind. And that there are only 2: true and apparent wind.

Despite my several posts to that effect, the 'ground wind' crowd continued to insist there was a '3rd' wind. I then, with the aim of allowing everyone to walk away from the discussion unscathed and heads held high, foolishly allowed myself to conclude there might be a 2 true wind reference points (by accepting that, all of us could have been right!).

Alas, by doing that, I exposed myself and sure enough you were quickly on my case. Both sides attacked simultaneously. I am all but finished.

I will go down in a blaze fanned by true wind (and not ground wind).

Thanks for noticing the 99% of my posts which were accurate and not concentrating on the one ambiguous statement I foolishly made

I'll get me coat
__________________
"It is good to have an end to journey towards; but it is the journey that matters in the end."
Ursula Le Guin
wolfaroo is offline   Reply With Quote
Old 27-05-2011, 13:10   #150
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 3,866
Images: 4
Re: What Heading Am I Really On ?

Quote:
Btw taking about " angles " is misleading that's merely because we have normally only " relative " angles on a boat. It's easy now to produce absolute angles TWA is the same as True wind direction.
TWA, TWS, TWD are terms, the meanings of which have been established by usage over decades. They pre-date GPS. Just because you believe that TWA should be the same as TWD doesn't make it so. It means what we agree it means, and I think you are in a distinct minority here.

Quote:
apparent wind combines all factors Leeway, tide weight anything that effects the boat. It's a real life value
Wind is a real life thing. All the factors you mention are real-life things. But current, and leeway don't enter into the AW calculations performed on a boat. AW is measured relative to the boat's bow, nothing more. If you are standing on a fixed point on the earth, measuring ground-referenced wind, and current, and observing a boat's course, speed, and leeway, you can certainly calculate the AW that boat will be experiencing -- these are real-world things. But from the deck of a boat, by convention, we measure AWA, AWS, TWA, and (usually) TWS relative to the water. We measure TWD relative to the ground.

"Angles" are extremely important on a sailboat, and the water-referenced AWA and TWA are useful numbers to have when optimizing and analyzing performance.

I believe that we all understand the concepts. The terms seem to be evolving. I don't particularly care what we call them, but I would like to at least agree on the definitions. I've presented my definitions, and I believe they are the common ones.
__________________

__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is online now   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What's Your Heading ? Windseeker Marine Electronics 17 12-02-2011 04:51
Crew Available: Anybody Heading to the Bahamas ? run aground Crew Archives 1 04-01-2010 10:40
Heading to Hawaii seancrowne Pacific & South China Sea 29 17-08-2009 21:30



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 12:09.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.