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Johan Hackman

What wind instrument?

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My Hanse 342 has a SimNet network installed with three IS20 Graphic and one IS20 Wind instrument. In the system there is also a IS20 masthead unit, a compass sensor, a GPS antenna and Maretron DST100 hull sensor. Now, I am not fully satisfied with the wind instrument and am looking to replace it with another brand. Since SimNet is NMEA2000, compatibility should not be a problem. I have already looked at the Garmin GMI10, which I have written about in another post in this forum.

Even if NMEA2000 is meant to be "plug-and-play" I see one major problem with choosing another brand. All calculated wind information, such as True Wind etc, is calculated from boat speed but the calibration of the boat speed is stored in the instruments and not in the sensors unlike, for example, depth. In the network only the measured boat speed is distributed and not the calibrated one.

When I calibrate the boat speed in one of my IS20 Graphics the wind information on the Wind instrument will change accordingly. It is not, however, possible to make the calibration in the Wind instrument itself so if I were to put the instrument in a network that would not have any Simrad instruments I would not be able to calibrate the boat speed in order to make the IS20 Wind instrument show the correct wind information.

The reason I have previously been looking at Garmin's GMI10 is that it is also capable of showing boat speed, which therefore must be possible to be calibrated. I have also looked at Furuno and Raymarine but I have not been able to retrieve enough information about their instruments to judge whether the boat speed can be calibrated in their wind instruments.

Has anyone else tried to combine instruments from different brands the way I am describing above?

Johan Hackman
Hanse 342 #306, S/Y Emilia

75 Replies

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  • Johan, the GMI 10 can derive true wind from a combination of apparent wind, GPS COG/SOG, and heading (if available). it doesn't matter what manufacturer's sensors are putting this data onto the NMEA2000 backbone.

    Here's the relevant info from the Garmin web site:

    Question: Can the GMI 10 display surface wind direction and/or speed when connected to a GWS 10 Wind Sensor?

    Answer:
    The GMI 10 does have the ability to display the surface wind direction and speed, but will need more information to calculate than what the GWS 10 Wind Sensor sends to it.

    The GWS 10 can only send the raw wind data like wind speed and direction. For the GMI 10 to be able to calculate surface wind direction and speed, it will need to know the boat's speed and heading. The best way to add this information into the GMI 10 is to connect the GMI 10 to a device that outputs GPS information over NMEA 0183 or NMEA 2000. If a GPS is not installed on the boat already, a GPS antenna can be used.

    Garmin offers two GPS antennas that will provide the needed data:

    GPS 17x NMEA 0183
    GPS 17x NMEA 2000

    The GPS antenna can read the speed of the boat based on the position changing when the boat is moving. The GPS antenna can also read the direction the boat is moving. However, when the boat is sitting still, the GPS antenna will not be able to provide a true heading. This is because the GPS does not know which way the boat is facing when the boat is stopped, therefore the GMI 10 cannot provide an accurate reading. To correct this issue, a heading sensor can be connected to the GMI 10 through NMEA 0183 or NMEA 2000. Garmin does offer a High Performance Heading Sensor that will use either NMEA 0183 or NMEA 2000.

    With the Heading Sensor and the GPS antenna connected to the GMI 10, the GMI 10 will be able to calculate surface wind direction and speed as it will know the boats speed from the antenna, and the boats true heading from the heading sensor.

  • Adam, thanks for your reply. Knowing that you have a few GMI10s, could you tell me the procedure of calibrating the boat speed on them?

    For comparison, to calibrate the boat speed in IS20 I have the choice to use SOG as a reference when I have a reason to assume that the water is still, or simply change the calibration factor. In my boat, the factor is somewhere between 1.05 and 1.44 depending on growth.

    Johan

  • Johan, I misspoke above. What I should have said is that the GMI 10 can derive ground wind, not true wind, using COG and SOG. I believe it can display true wind as well, but may require a way of measuring STW (eg, a paddlewheel), which we don't have. We will be adding an Airmar DST800 later this year so that we can display set and drift on the Garmin, but as we have a powerboat the difference between true and ground wind is not critical to us.

    I'm curious, though: What is true wind (wind speed and direction relative to the water, not the earth) used for?

    /afb

  • What true wind is used for? To move the boat forward. If it is a sail boat, that is. Haha!

    Sorry for the joke but it actually makes a bit sense. The wind relative to water is the wind that relates to your "feeling" of how much it is blowing. For example, if you are sailing six knots with a six knot ground wind from behind, and the current goes in the same direction at six knots you will feel that there is no true wind at all. (And then you won't in fact be sailing, but that's another story) For sailing, it is the wind that is blowing over the water that counts and not the wind that ruffle people's hair on the shore.

    The ground wind and true wind are different vectors and should be treated as such. The only conceptional problem occors when you say that the True Wind Direction is in reference to North when in fact it is also contains the current's speed and direction. I that respect it would be more correct to use ground wind.

    When my paddel wheel sensor packed in a few years ago my IS20s automatically turned to use SOG to calculate True Wind (which then became ground wind) and I didn't like it although I didn't sail in strong tides. It did not give me the same "feeling".

    Johan

    PS. In my over-simplyfied example above I am talking about the "feeling" of the true wind, not the apparent wind which obvioulsy is lower when you go downwind than upwind.

  • Maybe I should have spent a few more minutes trying to conceive a better example...

    That I wrote that I was making six knots with no wind only meant to say that I was motoring. It has no bearing on the example.

    What I meant was that if the water and the wind goes in the same direction at the same speed there will be no wind for sailing. The wind will blow over the beach but not over the water. Ground wind (in my example) will be six knots and true wind zero.

    Johan

  • But in that case, wouldn't apparent wind also be zero?

  • Not if you are motoring at six knots. With no true wind the apparent wind will be the same as you boat speed, opposite direction.

    Johan

  • Hm think I need some diagrams.

  • I would like to make an amendment to what I wrote in my first post "...but the calibration of the boat speed is stored in the instruments and not in the sensors unlike, for example, depth..".

    It is not really where the information is stored that matters, it is whether it is information that is contained in the NMEA protocol or not. As for depth offset, it is an NMEA2000 PGN (I hope that is what it is called). The depth itself is another. In other words, two PGNs containing information that is useful to display the correct depth is sent via the NMEA2000 network.

    When it comes to boat speed, only one PGN is broadcast and that is the often not so accurate speed measured by the paddle wheel. The calibration is done within the instrument and sent out as a proprietary message to synchronize instruments of the same brand. Simrad does not speak to, for instance, Furuno in this case. There would be no difference if the calibration factor was stored in the sensor itself, which to my knowing is not possible with the DST100.

    After having approached Garmin's support and received a very mumbling answer I have given up the idea of using GMI10 for my purpose. After some persitance with Furuno I have come to understand that boat speed can be calibrated within the wind instrument and I will try if it works with my setup as soon as the ice is gone in the cold country of Sweden. Before that I am prevented to go sailing and making any boat speed. The boat speed is zero at the moment...

    I hope this clarifies my initial post.

    Johan Hackman

  • Hi Johan,

    I don't know all the answers here, but I do think this deserves more study. For instance, if you look at Maretron's manual for the DST100, you'll see that raw depth and offset are two values of the same Depth PGN, #128267, not separate PGNs. Hence displays get both values. (But how they handle them seems to vary...some seem to just add them up and call it Depth, others seem to offer a choice of "Depth with Offset" or "Depth from Transducer".)

    By contrast, bits like wind wand offset is not a PGN value but is commonly a calibration factor that can be set, usually by the same manufacturer's display. Once set, the Apparent Wind PGN coming from the wand is corrected and all displays get the corrected value.

    Paddle wheel calibration is one the latter type, but it also seems that some paddle wheel sensors, like the Maretron DST100, don't have a speed calibration ability. Which may be why Simrad added its own routine (which I hadn't realized).

    But I believe Furuno is a special case, which I once wrote about: http://goo.gl/VSUGY

  • Thank you Ben,

    You kind of confirm what I wrote apart from me thinking that a PGN could just carry one value, but on the other hand that is a minor point.

    I have read your post "Another Calibration Road Taken" many, many times along with your "don't try this at home"-tests of mixing different manufacturers' NMEA2000 equipment. It has been invaluable information to me. Thanks yet another time, it is your blog that makes all this possible!

    What is easy to forget when doing a lab test (especially if you are a power boater) is that boat speed is not just how fast the boat goes. It is also a figure for the wind created by the boat and that is what us sailors want to subtract from the apparent wind to get all sorts of True Wind (TWA, TWS, wind direction in reference to North etc). In order to see if this "calculated wind" comes out right you need to add boat speed to the data. (I am only waiting for spring to come so I can complete your test)

    As far as I know, Simrad instruments synchronize themselves when a calibration is done the same way you describe Furuno do. They are similar in this respect but Simrad's IS20 Wind does not have the feature whereby you can calibrate within that instrument itself (you will need a Combi or Graphic) whereas Furuno has this feature which allows me to mix the two brands. I will only have to take the calibration factor from my Simrad instruments and feed it to the Furuno wind instrument.

    Johan Hackman

  • There is only one "wind" PGN, but it contains a field stating what the reference plane is. For instance, on my own boat's network with a Simrad wind sensor (as well as a PB200) I get the following in a typical quarter second:

    2010-09-12-10:47:22.780 2  36 255 130306 Wind Data:  SID = 10; Wind Speed = 2.98 m/s; Wind Angle = 337.1 deg; Reference = Apparent
    2010-09-12-10:47:22.850 2  13 255 130306 Wind Data:  Wind Speed = 3.3 m/s; Wind Angle = 306.7 deg; Reference = Apparent
    2010-09-12-10:47:22.961 2   2 255 130306 Wind Data:  Wind Speed = 2.88 m/s; Wind Angle = 263.3 deg; Reference = True (boat referenced)
    2010-09-12-10:47:22.964 2  13 255 130306 Wind Data:  Wind Speed = 3.3 m/s; Wind Angle = 306.9 deg; Reference = Apparent
    2010-09-12-10:47:23.015 2   2 255 130306 Wind Data:  Wind Speed = 2.88 m/s; Wind Angle = 277.5 deg; Reference = True (referenced to North)
    2010-09-12-10:47:23.077 2  36 255 130306 Wind Data:  SID = 11; Wind Speed = 1.33 m/s; Wind Angle = 296.1 deg; Reference = True (referenced to North)
    

    There are three source devices in play here:
    #13 - the wind instrument at the top of the mast
    #2 - the autopilot computer
    #36 - the Airmar PB200

    The Simrad wind instrument (#13) only sends out Apparent wind data.

    The PB200 (#36) uses the speed input it gets on the bus (failing that it will use SOG) and it's own Apparent wind data plus the compass direction of the boat, allowing it to calculate True wind referenced to North.

    The Simrad AC42 autopilot computer takes the information from the wind instrument, the compass and the speed instrument, computes true wind both referenced to the boat (which is what you want displayed on the Wind instrument) and referenced to North (which is what you want to log in a logbook.)

    In my setup the True wind is calculated by the autopilot computer (device #2). Thus there is no need for the IS-20 wind instrument, in this particular setup.

    Johan you also assert:

    the calibration of the boat speed is stored in the instruments and not in the sensors unlike, for example, depth. In the network only the measured boat speed is distributed and not the calibrated one.

    I don't think this is true, the Speed PGN 128269 contains "true" speeds in m/s, not "paddle units". You may also want to read DST 200 user manual that documents the calibration PGNs.


  • Thank you, Kees. I now have 62 pages of user manual to read - but I am looking forward to it as it seems to contain a lot of useful information that I have actually been looking for. Before I head for the sofa with a printout of the manual I would like to add a few things though.

    When your PB200 calculates True Wind from the speed input from the hull sensor and its own Apparent Wind, how is that broadcast on the network? I don't believe there is a PGN for that?

    You got me completely wrong when it comes to the speed PGN, probably because I used the expression "measured boat speed". I am Swedish so forgive me if there would have been a better expression. My Maretron DST100 is a Smart sensor, as is Airmar's DST800 (or DST200 for that matter) which means that they indeed send out the boat speed and not the paddle units. If they'd sent out the paddle units they would not be NMEA2000 compatible and you would need a "black box" of some sort for conversion. I used to have two sensors (which were called D200ST) consisting of a paddle wheel sensor (that I believe was "analog") that went into a depth sensor which converted and sent out NMEA2000 Depth, Speed and Temperature data.

    What I meant was that the speed reported from the sensor may not always be the correct boat speed. The actual boat speed might be more or less than the "reported" speed because of growth and hull shape etc, in which case you want to multiply it with a calibration factor. I does not matter where this factor is stored, be it in the sensor or the instruments, it is the fact that the factor is not contained in any NMEA2000 PGN that makes it difficult to combine instruments from different manufacturers. The same goes for the wind sensor offset. I you for any reason have not mounted the sensor directly in line with the boat's center line you might want to compensate for it by adding a number of degrees to the apparent wind angle readings. This figure is not contained in any NMEA2000 PGN (like Ben said earlier) and has therefore to be sent between instruments in proprietary messages.

    I have already tested Furuno's wind instrument against my Simrad setup to see that if I change the wind sensor offset on the Furuno wind instrument it will show a different wind angle from the angle displayed by Simrad. This confirms that this calibration factor is proprietary.

    Johan Hackman

  • Clearly, I failed in my explanation. There does not need to a wand offset PGN because once the value is set in the wand, the AWA PGN is corrected for all devices that receive it. You would need an proprietary PGN if the offset only lives in another device, which why Furuno calibrations are only seen by other Furuno devices (I'm pretty sure).

  • Ben, I liked your previous explanation, it made sense. Don't change it. ;)

    What I just confirmed by hooking up Furuno's wind instrument to my Simrad setup is that the calibration only lives in one of the instruments, in this case the Furuno. If I set the offset to 40 degrees, Simrad and Furuno will show figures that differ 40 degrees.

    I therefore believe that the AWA is not corrected by the wind vane. The calibration I make in the Furuno wind instrument does not seem to affect the data from the wind vane.

    Johan Hackman

    PS. I could be wrong in anything I say so please bear with me if it turns out I am.

  • John says:

    When your PB200 calculates True Wind from the speed input from the hull sensor and its own Apparent Wind, how is that broadcast on the network? I don't believe there is a PGN for that?

    Yes there is a PGN for that. I recommend that you head over to my website and take a look at the reverse engineered PGN data, look for PGN 130306. As I showed earlier in my log the same PGN 130306 is sent out twice, with different "Reference" fields.

    Next you say


    What I meant was that the speed reported from the sensor may not always be the correct boat speed. The actual boat speed might be more or less than the "reported" speed because of growth and hull shape etc, in which case you want to multiply it with a calibration factor. I does not matter where this factor is stored, be it in the sensor or the instruments, it is the fact that the factor is not contained in any NMEA2000 PGN that makes it difficult to combine instruments from different manufacturers.

    The problem is not the display instruments, it's the sensors responsibility to give out correct information. Now most instruments will have a setup routine that allows you to calibrate but this should send instructions to the sensor that it should put out a corrected value. The Airmar sensors work this way, at least. I think Ben has found that -some- instruments also allow in-instrument adjustments but I can't remember which ones. That approach doesn't scale well as you add instrument displays though, so maybe we should be glad it's not how most devices work.

    The same goes for the wind sensor offset. I you for any reason have not mounted the sensor directly in line with the boat's center line you might want to compensate for it by adding a number of degrees to the apparent wind angle readings. This figure is not contained in any NMEA2000 PGN (like Ben said earlier) and has therefore to be sent between instruments in proprietary messages.

    I have already tested Furuno's wind instrument against my Simrad setup to see that if I change the wind sensor offset on the Furuno wind instrument it will show a different wind angle from the angle displayed by Simrad. This confirms that this calibration factor is proprietary.


    Yes, calibration is proprietary so you'll need at least one display / software package for each brand of sensor. The exception is the Airmar DST200/800, most brands OEM this so there are a number of brands that can calibrate that particular device.
  • My earlier email where I cut & paste a bit of log from my instrument data was truncated, so it didn't show what I meant to show. Here it is again but this time readable, hopefully:


    ... 2 36 255 130306 Wind Data: SID = 10; Wind Speed = 2.98 m/s; Wind Angle = 337.1 deg; Reference = Apparent
    ... 2 13 255 130306 Wind Data: Wind Speed = 3.3 m/s; Wind Angle = 306.7 deg; Reference = Apparent
    ... 2 2 255 130306 Wind Data: Wind Speed = 2.88 m/s; Wind Angle = 263.3 deg; Reference = True (boat referenced)
    ... 2 13 255 130306 Wind Data: Wind Speed = 3.3 m/s; Wind Angle = 306.9 deg; Reference = Apparent
    ... 2 2 255 130306 Wind Data: Wind Speed = 2.88 m/s; Wind Angle = 277.5 deg; Reference = True (referenced to North)
    ... 2 36 255 130306 Wind Data: SID = 11; Wind Speed = 1.33 m/s; Wind Angle = 296.1 deg; Reference = True (referenced to North)

  • I thought it was truncated. Now it makes sense, thank you!

    Johan

  • Exactly , Furuno is the exception . Maretron , Garmin, airfare andmaybe Simrad all put the offset in the sensor.

  • Ok, so then I was wrong when I said that it didn't matter where the calibration is stored. Sorry!

    If Furuno is an exception, I think Simrad is too. The other brands I have no experience with.

    Johan

  • I'm pretty sure that Simrad does it like the others, and am almost certain that an IS20 will only calibrate Simrad sensors. However, boat speed may be an exception because the Simrad (Airmar) triducer doesn't seem able to accept a boat speed calibration factor.

    Incidentally, the advantage of the Furuno way is that it works with all sensors.

  • Ben, the Airmar triducer not only accepts boat speed calibration, it even allows for linearization of the paddle by setting up to 25 different calibration points. See the manual on page 23, PGN 126720 (Calibrate Speed).

    I don't know which tools allow such sophisticated calibration, but the doc clearly specifies that the sensor supports this. I feel a hobby project coming up :-)

  • That's good news, Kees, both the capability and your interest. I don't think that even Airmar's own WeatherCaster software can do that calibration, or at least couldn't the last time I looked.

  • I realise even more now than I did before that compatibility is not really the strength of NMEA2000 or should I say, its implementors. I seem to be lucky to have found two systems that, at least for now, seem to work together for my purposes. I mean, one system calibrates here and another there, one sensor can be calibrated but another can't, and at the end of the day it is up to the manufacturer to decide how they want to do it and they don't want to let us know what they have done so we can combine the gear we want.

    I would like to thank you for the information you all have given me. I am going to contemplate and learn from it and will get back with a report how my Furuno wind instrument is getting along with my Simrad/Maretron gear.

    Johan Hackman

  • Here's an update to show that I have done my homework.

    When I tried to change the wind vane offset in one of my Simrad IS20 Graphic instruments the wind angle changed on all instruments including the Furuno FI-501.

    When I changed the offset in the FI-501 the wind angle only changed in that instrument. This is what I tried already in my first test of the instrument and which I talked about in a previous post. This made Simrad and Furuno show different wind angles.

    The conclusion is that Ben is perfectly right (and I didn't mean to contradict) when he says that Simrad saves the calibration in the sensor and that the correct data is read by any instrument regardless of brand. The Furuno instrument will not save the calibration in the Simrad wind vane but will work with the Simrad wind vane because the calibration is done within the instrument. I don't think it would work the other way round though. If you only had a Simrad wind instrument and a Furuno wind sensor one would not be able to influence the other in terms of calibrated data. Only raw data would be displayed and used for calculations.

    So far I have managed to eliminate one of my initial two worries. As long as the wind angle offset is stored in the wind sensor and the calibrated data is broadcast as an NMEA2000 message any instrument will display the correct angle. As I have a few Simrad instruments and a Simrad wind sensor I can set the offset at any time.

    My other worry, the boat speed calibration, is still a bit dodgy to me. It seems the choice of sensor is crucial. If you choose an instrument that wants to store the calibration in a sensor that will not allow it you will not be able to calibrate it. Then it is better to choose an instrument like Furuno's FI-501 that will store the calibration in the instrument.

    Johan Hackman

  • Thanks, Johan. On the rare occasion that my wife admits that I'm right about something, I sometimes ask her to say it again...but I relent in your case...;-), and in fact just wrote Airmar trying to find out how those triducer STW calibrations can be done.

  • From Airmar:

    "We have been testing a version of Weathercaster that allows for paddle-wheel calibration. It is not yet released. Some displays, like Garmin GMI 10 also allow for calibration on the display."

  • I think it is time to make a conclusion now that I have an answer to my original question. The ice has finally broken up and I have been out sailing testing my new acquisition.

    Yes, there is an analog wind instrument that will work with my SimNet setup. The only thing I have to do is get a SimNet-to-NMEA2000 adapter and connect the instrument. That instrument is Furuno's FI-501.

    The reason the FI-501 works with my Simrad IS20 system is that you can change the boat speed calibration factor in the FI-501. It will thereby display True Wind information correctly as it can subtract the correct boat wind from the apparent wind.

    My boat is a Hanse and all new Hanses to my knowledge come with IS20. I have written a long post with pictures at www.myhanse.com about my search for an alternative to the IS20 Wind. The post can be found here: http://www.myhanse.com/forum_posts.asp?TID=5000 and contains some information that could be useful for someone with the same concern.

    Apart from solving my own problem I have learnt an immense deal about NMEA2000 from all you contributors to this thread. I want to thank you yet another time.

    Johan Hackman
    S/Y Emilia
    Stockholm
    Sweden

  • Those are great posts, Johan, but even more fun was then finding your home site with wicked good guitar playing and your own sailing video. Don't be shy:

    http://www.johanhackman.se

  • I'm a bit fuzzy on why you need Speed Over Water (SOW) in addition to Speed Over Ground (SOG) to calculate true wind speed or direction. You can be sailing 6kts into a 6kt current. Your SOW is 6kts but your SOG is zero. (Same as if I was anchored in a 6kt current.) Since you are in effect not moving, Apparent wind IS true wind, is it not?

  • It's confusing but "True Wind" is defined, and hence calculated, in two different ways.

    Have a look at this entry:

    http://www.panbo.com/archives/2009/10/airmar_cs4500_part_ii_reliable_true_wind.html

  • I have been involved in thousand and one discussions about what true wind is. It seems people's view on what "Truth" is vary a lot.

    To me (and most wind instrument manufacturers), True Wind is Apparent wind minus Speed Wind. That gives you the wind that blows across the water surface, i.e. the wind you use for sailing. It is the True wind to me because it tells me the wind where I am, which is in a sail boat. It does not tell me the wind some other place, like a nearby island. In my boat, the wind that blows across the shore is not interesting when I am sailing. To me, that would be a False Wind.

    The apparent wind (which is the only wind you can measure) consists of two winds - the true wind blowing across the water and the speed wind. The speed wind is the wind generated by the boat's speed forward, just as you will find it very windy if you stick your head out the car window while driving. If you substract that from the apparent wind you will get the True wind blowing across the water surface. Remember, velocity is per definition a vector, i.e. it has both a size and a direction, just as an arrow drawn on a piece of paper. When you are driving the velocity of your car is also a vector but since the direction is always directly forward you tend to forget about it. What I am saying is that substracting speed wind from apparent wind is not just substracting one number from another. You need to use vector summarization which practically is drawing triangles on paper. You will see what I mean if you follow Ben's link.

    Apparent wind and True wind are the same only if you are not making any speed through the water. If you are anchored in a 6 knot current you are in fact making 6 knots through the water with your boat and apparent and true wind readings are bound to be different. If you weigh the anchor and start drifting with the current and you therefore make no speed through the water, apparent and true wind will be the same. Your SOG will then be 6 knots but that is irrelevant when you are talking about the wind that blows at the moment.

    Johan Hackman

  • PS. "Speed wind" is an expression I use since that is what it is called in Swedish. (It is actually called "fartvind" which might sound funny to a speaker of the English language.) There might be a better expression in English. If so, please let me know.

    Johan

  • Color asked "I'm a bit fuzzy on why you need Speed Over Water (SOW) in addition to Speed Over Ground (SOG) to calculate true wind speed or direction."

    I would add the clarification to the above that SOG (a measurement taken with GPS) is not used in the calculation of true wind angle and velocity. Only need SOW (measured with a paddle wheel).

  • Then maybe it should be clarified that it is really Speed Through Water (STW) rather than Over Water. Unless you are windsurfing.

    Johan Hackman

  • I agree that STW is the more common and accurate acronym. Tt's also true that some instruments will let you use SOG instead of STW for calculating True Wind, and that some boaters prefer that version of True Wind. For instance, it's better for monitoring actual ground wind changes as it corrects for the current set/drift vector (partially at least).

    Frankly, I think some sailors are a bit arrogant to claim that their preferred True Wind -- the real direction and speed relative to the water surface -- is the only True Wind. A lot of people prefer to think of True Wind as the real direction and speed relative to the earth's surface, and I doubt they're going to change their mind.

    Note that pro race navigator Mark Chisnell calls it Sailing Wind in his book Chisnell on Instrument Techniques.

    http://www.markchisnell.com/technical.htm

  • I don't mean to be an arrogant sailor but to me it is important to keep things apart. If I don't know the difference between wind across the water and wind across land I will be a lesser sailor.

    I will elaborate this a bit and hope you will bear with me.

    How do you define wind? A moving mass of air is the simplest answer. But, you must take into consideration in relation to WHAT the mass of air is moving. It could be in relation to land, which will be stationary in relation to this planet, or water that will or will not move. Compare with your car - if you say you are driving at 100 km/h it is implied that it is in relation to the road. No one will ask you in relation to what your car is moving. However, you could also claim that you drive 108 000 km/h because that is the speed of the earth in its orbit around the sun and the car is traveling with the earth. It is true but not relevant. You would get a speeding ticket if you claimed that.

    So it is horses for courses. Each to their own. But it is good to know the difference between different types of true wind.

    (An example: your boat is in waters where the current is 6 knots. A mass of air is moving across land at 6 knots in the same direction. The true wind ashore is 6 knot but the true wind out on the water is 0. You can choose for yourself if you want to say it is a breeze or wind still.)

    I am just trying to shed some light on a subject that many people find confusing.

    Johan

  • You sort of lost me, Johan, but you did get me thinking about celestial mechanics and the upcoming Equinox. I'm planning an entry about it. I'll also be making the case that the type of True Wind that most deserves the title is relative to True North. I just found a paper that seems to back me up pretty well:

    http://coaps.fsu.edu/woce/truewind/paper/index.html#tab1

  • If we call that flavor of true wind relative to ground, "Ground Wind", and to the water surface "True Wind"

    The part of my brain navigating wants to know the Ground Wind, and the part of my brain that wants to know is my boat going fast in these wind conditions, equates wind conditions to True Wind.

    Getting ground wind information of any accuracy is a challenge in the current infested waters of long island sound.

    Getting true wind information is really simple with a combination of a motion corrected Airmar PB200 and a foul proof Airmar CS4500 STW sensor.

  • To be more granular ...

    The part of my brain navigating wants to know the wind relative to ground in degrees magnetic (just like my ship compass & chart plotter ) and the part of my brain that wants to know is my boat going fast in these wind conditions, equates "wind conditions" to be True Wind relative to bow.

    Ben, what is the history of true wind relative to water as you know it? Do you take away anything that it wasn't included in this paper ?

  • One take away is that merchant mariners, oceanographers, and meteorologists define True Wind as relative to earth, which is really not surprising when you consider True North, True Headings, the Lat/Long system and other fundamentals of nav science.

    I get the term Ground Wind and that's what some instruments use, but calling Apparent Wind corrected for boat speed but not for water motion "True" has never made much sense and is obviously confusing to everyone who associates True with True directions.

    I don't know the history of performance sailing "True Wind" but obviously it was much easier to compute before GPS came along. I don't think that's true anymore though. Not many boaters have as accurate an STW sensor as you do, Dan, but most everyone has quite accurate COG/SOG when underway. Leaving out the unusual situation of sailing in very light breezes and strong currents True True Wind/Ground Wind is easy to calculate.

  • Small point. I do not believe, actually I am certain, the CS4500 is not more accurate than the paddlewheel, just more reliable in that it always works (sensor never dirty). The outcome is I get reliable STW readings, all 50 times I sail each year, and hence reliable true wind display.

    Big point. I wasn't aware (for recreational boats in coastal waters) that ground wind direction can be calculated with apparent wind + SOG. Really? With any useful precision for most boaters? Is it as good as say +/- 20 degrees for most boaters?

    I thought the setting (substitute SOG for STW) was too help give the sailor useful true wind speed period. (the direction component, degrees off the bow, was noise unless the set & drift was zero). Yes/No ?

  • Dan, I don't know how many instruments do a full COG/SOG correction to the apparent wind/heading vector, but I think that's because they're mainly designed for sailors who just want their unusual version of True Wind (whose value for performance monitoring I understand). But doesn't your PB200 output fully calculated True Wind relative to earth surface and doesn't Airmar call that True Wind not Ground Wind? And why couldn't it be quite accurate?

    As far as just using SOG to correct Apparent to True relative to earth, remember that most boats go faster than sailboats and often with a COG quite close to Heading. So, yes, I think it can work pretty well much of the time, and often better than True relative to water surface because STW is so often a flaky value.

  • I don't recall that part of the PB200 feature set, and if its results would be any different from what I could expect from my Raymarine Chartplotter. At the time I decided to take the PB200 apparent wind output only and leave it to the chart plotter to calculate true and ground wind.

    Change sub topic ..

    You wrote above, in regards to a future entry, "I'll also be making the case that the type of True Wind that most deserves the title is relative to True North".

    For the date of that entry, do you know a couple of people you can get forewarn and get to Panbo for a lively debate and make a counter case? Or is what I know as True Wind destined to become "fartvind" ?

  • Please keep in mind that this thread was started by me to find a suitable replacement for my Simrad IS20 Wind instrument. I wanted an NMEA2000 instrument that could be calibrated for boat speed. In the end I found that Furuno has such an instrument and I have been using it successfully since. In other words, I have been talking about the True Wind that is useful for sailors all along.

    I agree that there might be more than one True wind. The weatherman will give you the wind across land, for instance. Please note that he/she will give you a vector, i.e. an entity with both size and direction. If the wind tomorrow will be SW 10 knots, SW is the direction and 10 knots the size.

    If you want to work out the sailor's true wind in tidal waters from the weatherman's true wind you will have to take the vector "wind" and the vector "current" (direction and speed) and do a vector summarization to find the resulting wind. This is a bit backwards when you consider that you only have to subtract the speed wind, the "fartvind", from the apparent wind to get the same result. Plus the apparent wind reported by your wind sensor is measured while the weatherman's wind is just forecasted.

    If you look back at the old days before electronics, the only way to tell the wind was a wind vane (called Windex in Swedish) at the masthead. It would only give you the apparent wind direction, and not the wind speed. I don't know the history but I guess electronics had to be invented to use cups to measure the speed. I don't know if there was a mechanical solution to this, like the sum log. Anyway, when you could take the information from the log (also a vector - boat speed and direction, direction in this case the direction of the bow) and combine it with the vector apparent wind you could compute the true wind. At that time, GPS was not yet invented.

    Then the electronic compass was invented and you could compute what Simrad choose to call TWD, True Wind Direction. That is the wind in relation to North. For example, if your heading is 270 degrees and the wind is 45 degrees from starboard the TWD is 315 degrees, i.e. NW. I use this a lot on my boat, not for trimming obviously, but for planning. It is worth noting that with a leeway and/or currents the figure will not be completely accurate.

    I want to make it even more complicated and I think Dan was touching this. If you use SOG to substract boat wind (or fartvind) from the apparent wind you only use one number. SOG is coupled with COG and as it is a vector one cannot live without the other. If your boat speed is 6 knots and your SOG is 6 knots you tend to think they show the same thing. On the contrary, the direction of your boat speed is always implied to be in the direction of the bow while the direction of your SOG could be just anything. You could be moving at 6 knots backwards or sideways and your display would still say SOG 6 knots.

    Johan Hackman
    www.johanhackman.se

  • Dan, True Wind as calculated using GPS and Heading sensors has always been a top listed feature of the PB200, as in:

    "The internal, WAAS GPS engine and three-axis solid-state compass provide both Apparent and True Wind Speed and Direction without the need to tack on additional sensors."

    and

    "Also unique to the PB200 is that the 3D accelerometer and rate gyro are temperature compensated, resulting in precise tilt and rate-of-turn data. This allows the PB200 to accurately measure True Wind Speed and Direction even when tilted up to 30°."

    http://www.airmartechnology.com/2009/products/marine-product.asp?prodid=105

    So, Dan, isn't that a True Wind that you think of as Ground Wind?

    Sorry to stomp around in your thread, Johan, but what got it started again was someone asking about how True Wind is calculated and I don't think he got a full answer when told that STW and Apparent is all it takes. Hopefully this is a constructive discussion ;-)

  • It is a constructive discussion indeed. I meet a lot of sailors who don't understand how to use their instruments and I am just trying to help a few of them. If no one writes about this the instruments will never be used the way they were intended to.

    Johan

  • Yes, top features of the PB200. But as Airmar feared, when the sailboat goes up and down 4 foot waves, that didn't work out so well, so I turned off that part of the output and used only the wonderful motion corrected apparent wind features along with some others and leave it to the chart plotter to provide true wind relative to water and ground wind.

    "So, Dan, isn't that a True Wind that you think of as Ground Wind?" --> No, I have always thought of true wind as the wind speed and wind direction of the wind relative to water in degrees +/- from the bow. For a time I did use that output from the PB200, and it performed exactly that way.

    Am I missing something?

  • Gosh yes! Dan, you're contradicting yourself. Up above you stated that "I would add the clarification to the above that SOG (a measurement taken with GPS) is not used in the calculation of true wind angle and velocity. Only need SOW (measured with a paddle wheel)." But the PB200 calculates True Wind using SOG (and COG, HDG, etc. but not STW).

    So the PB200 calculates True Wind relative to the earth surface not relative to the water surface. Whether True Wind is expressed relative to a boat's bow or True North is just how it's expressed, not how it's calculated (though sailor's True is usually off the bow).

    Am I missing something?

  • Ah ... glad I asked !! You must think I am nuts.

    I will make the case that I am not crazy.

    The PB200 does take as input STW, and when I had the PB200 configured to output true wind over NMEA-0183, I had the PB200 in the default configuration where it looks for STW from a paddlewheel and provided TWA in degrees +/- 180 degrees off the bow and TWS in knots.

    So from my point of view, what I wrote above is entirely correct. I wrote "I would add the clarification to the above that SOG (a measurement taken with GPS) is not used in the calculation of true wind angle and velocity. Only need SOW(STW) (measured with a paddle wheel)."

    And what you wrote above I view as an option on the PB200, that option being to use SOG instead of STW as you wrote "But the PB200 calculates True Wind using SOG (and COG, HDG, etc. but not STW)"

    Ben, to my way of thinking, the obvious reason to use such an option, is to avoid the labor and mess of cleaning the paddle wheel twice a month. Yes ? Also the option makes the PB200 a nice fully contained sensor platform without depending on getting the STW input.

    The part of the PB200 I am fuzzy about, is the feature set about reporting wind direction in degrees true or magnetic. Didn't use that.

    Let me know if I didn't clear things up. I don't want you to think I am not grasping this correctly, and would take the step to crack open the manual, circle the relevant pages, scan, and email them to you.

    Johan ... thanks for letting us borrow your thread.

  • Dan, I don't think you're crazy but, wow, are you stubborn. How in the world did you persuade yourself that the PB200's 'default' True Wind mode uses STW when the very first paragraph of the product description proudly states that it can "provide both Apparent and True Wind Speed and Direction without the need to tack on additional sensors"?

    Let's look at the manual
    http://www.airmartechnology.com/uploads/installguide/PB200UserManual.pdf

    Page 1:

    "In addition to the above directly measured parameters, the PB200 WeatherStation is able
    to calculate the following values as well, if the necessary data are available:
    · True wind speed and direction
    · Heading relative to true north
    · Apparent wind chill temperature
    · True wind chill temperature
    · True wind speed relative to water (with optional Airmar Smart speed sensor, not included)"

    If you search the whole PDF for "True Wind" you will see that Airmar consistently references it either as True Wind Speed/Direction OR True Wind Speed/Dir relative to the water. In other words they treat True Wind relative to ground as the primary definition. Which is entirely consistent with the fact that this is primarily a WeatherStation, not a sailing instrument.

    I don't know what's so hard about this, Dan, but there are many people who think that True Wind relative to ground is a perfectly valid definition.

    So, no, it has nothing to do with avoiding "the labor and mess of cleaning the paddle wheel twice a month."

    And here's more evidence, a description the NMEA 2000 PGN #130306 called "Wind Data"

    "Direction and speed of Wind. True wind can be referenced to the vessel or to the ground. The Apparent Wind is what is felt standing on the (moving) ship, I.e., the wind measured by the typical mast head instruments. The boat referenced true wind is given by the vector sum of Apparent wind and vessel's heading and speed though the water. The ground referenced true wind is
    given by the vector sum of Apparent wind and vessel's heading and speed over ground."

    Could it be any plainer? As I've been saying all along, there are two definitions of True Wind, except that some sailors think there's only one. Time to give it up, Dan?

  • I will do better than give up.

    Yes I am stubborn and even pulled out the 2008 version of the Airmar manuals I remember.

    I found what I was looking for, but also came across a bunch of text on true wind I thought at the time was confusing and superfluous. Clearly I didn't grasp at the time the other True Wind was the primary target of their product.

    I will approach true wind very differently from now on.

    Thank you Ben for hanging in there and setting me straight !!

  • Ok, I know that I have delivered some confusing statements. I will try to ask a question instead:

    Q: How do you calculate True Wind Over Ground when you are on a sail boat? The data at hand is Apparent Wind (wind angle and wind speed), Speed Over Ground, Course over Ground and Heading.

    For comparison, True Wind across Water is simply calculated by vector summarization of Apparent Wind (wind angle in reference to the bow and wind apparent wind speed) and boat wind (speed and direction, which is in the direction of the bow).

    I think it needs to be clarified how the calculation in the above question is done in order to understand how "true" wind works. So come on, show me your math skills! ;-)

    Johan

  • Thanks, Dan!!!

    Johan, a line in the Airmar manual (which is excellent for tech heads, by the way) reveals True Wind math pretty well:

    "True wind data is provided in the $WIMWD and $WIMWV (theoretical) sentences if SOG/COG,
    heading, and magnetic variation data are available from the internal GPS and compass."

    So the regular Apparent Wind vector (angle and speed relative to bow) is first referenced to True North using boat Heading and magnetic variation. Then the SOG/COG vector, which is already true boat motion relative to True North, is simply subtracted and, voila, you have True Wind direction and speed (aka Ground Wind).

    In my early years as a navigator (decades actually) COG and SOG were damn hard to calculate, but GPS turned that situation upside down. Now I think that they are the most precise data points on many boats.

    Now a question for you and Dan: Is there any value to sailing True Wind (relative to water) except as a base line to gauge if a boat is sailing its best? I realize that this is very important to sailors and has largely driven instrument development but why should powerboaters and others care?

  • Bravo, Ben! What you just proved is that you need more than just SOG to make that calculation. Most people want to just replace STW with SOG because they think it is more accurate. I am also glad to see you use the word "vector" which is an important word within the context.

    You ask about the use of True Wind on a sail boat. I tend to use True Wind Speed at all times to keep myself updated with wind conditions and Apparent Wind Angle for performance, especially upwind. Plus I use TWD (True Wind Direction in reference to North) a lot. I see no use for Apparent Wind Speed when I am sailing. My autopilot (Simrad AP24) automatically changes from AWA to TWA when in wind-steering mode and I am sailing downwind, to prevent crash gibes. So the autopilot is also relying on the same true wind reading that I am.

    I believe this entire thread is nonsense to power boaters but both Simrad's and Furuno's wind instrument were designed for sailors.

    Johan

  • Of course it's vector math, Johan, it's just that many instruments don't have the data inputs and/or horsepower to do full vector solutions. I guess I'm getting to be an old geezer but I visualize a lot of navigation in terms of vector graphics, because that's how we used to do it. Check out this True Wind maneuvering board solution from an old American Practical Navigator: http://goo.gl/BMK52

  • What Johan wrote resonates with me.

    To Ben's question: In addition to baseline, I pay attention to TWrw for sail trim controls (back stay positions, halyard tension, etc.) and also to decide if on my next tack I can stick with my headsail selection. When cruising to decide in advance if I will reef, even if I will tack or hold my course. In 2 knots of current, 8 knots TWrw on one tack, can be 5 knots TWrw on the other ... a tacking choice that will result in cries for an engine start.

    For a powerboat? I can try to relate to my use of Breeze Pleeze when motoring, but I don't pay attention to TWrw except to think about the potential to raise the sails or how to increase apparent wind speed to cool off on a hot day. For a powerboat, that wouldn't be a consideration, eh?

  • Johan what your wrote about using wind on the sailboat resonates with me (cool feature that the autopilot uses true wind also).

    Are you sharing this Ah Ha moment where Ben brought me, or are you still in the place I was? Or somewhere in-between?

  • I am still in the same place, I have not changed. ;-)

    I think I read the Airmar manual differently to how Ben reads it. My point of view is the sailor's and I can find proof in the manual that "True wind" is the wind in reference to the water, if I look for it. The manual only says that the unit cannot provide this information unless you connect a speed sensor. It makes sense as the WeatherStation is supposed to be mounted at the masthead which is the furthest away from the paddle-wheel. The paddle-wheel could not be built into the WeatherStation, if you see what I mean.

    I would not use True Wind Over Ground on my boat even if Ben throwed it after me and paid me to use it. And it is not because I think he is wrong, it is just because it is not useful for me as a sailor.

    I don't know how accurate the WeatherStation is but would fear that too many parametres that need to be brought into a calculation will play with the accuracy if you want to go all the way to calculate true wind.

    In the case of True wind in reference to the water you only need too parametres: apparent wind and boat speed. Considering the both are vectors you are dealing with four numbers. There is only one of these that you need to calibrate and that is the boat speed (which is how this thread started).

    I would love to have a better speed sensor, like the CS4500, and perhaps also an ultrasonic wind sensor like the PB200. What I have though is a "Motion Sensor" that is a self-calibrating compass, rate gyro and GPS sensor. (http://www.seadataweb.com/Products/MotionSensor/Default.aspx) It will compensate for the errors created by the movements of the mast when you are sailing.

    Johan

  • I think I just found out that "headwind" is the proper English word for what I have called "speed wind", "boat wind" or "fartvind" (Swedish) in this thread.

    Johan

  • Johan, look at the manual again maybe? Ben has me fully believing the the PB200 was designed for that other true wind, relative to earth.

  • If I understand it correctly, the PB200 was designed to give you True Wind in reference to ground AND True wind in reference to the water - as soon as you connect a speed sensor.

    I am not going to read the manual any more careful than that as I cannot afford a WeatherStation. :-(

    I find it very important to have good sensors and have them calibrated correctly (hence this thread). I am constantly looking for better gear but it is both expensive and difficult to judge whether they will give you that little extra.

    Johan

  • You guys are getting silly. I don't think I persuaded Dan of anything. I just pointed out the facts he was denying.

    The Airmar literature always calls Ground Wind simply True Wind and a top feature of the PB200 is that it can output "True Wind Speed and Direction without the need to tack on additional sensors." Notice that they did NOT say True Wind Speed and Direction relative to ground.

    The PB200 will also output Water Wind which Airmar always calls "True Wind relative to water", presumably in deference to zealots like yourselves and reality.

    It's abundantly clear which "True Wind" Airmar considers true, and maybe they'll be the first to adopt Water Wind.

  • In just what way is any of us being "silly"? I don't understand that statement.

    Johan

  • No harm meant, Johan, (and "silly" is a light word here) but your insistence that Airmar treats Ground Wind and Water Wind equally as True Wind combined with your unwillingness to look at the manual is absurd. It will take you all of 10 minutes to learn that Airmar does not treat them equally. As I wrote above:

    Let's look at the manual
    http://www.airmartechnology.com/uploads/installguide/PB200UserManual.pdf

    Page 1:

    "In addition to the above directly measured parameters, the PB200 WeatherStation is able
    to calculate the following values as well, if the necessary data are available:
    · True wind speed and direction
    · Heading relative to true north
    · Apparent wind chill temperature
    · True wind chill temperature
    · True wind speed relative to water (with optional Airmar Smart speed sensor, not included)"

    If you search the whole PDF for "True Wind" you will see that Airmar consistently references it either as True Wind Speed/Direction OR True Wind Speed/Dir relative to the water. In other words they treat True Wind relative to ground as the primary definition. Which is entirely consistent with the fact that this is primarily a WeatherStation, not a sailing instrument.

  • Too funny! When just searching for info on autopilots steering to "true wind" I came across this forum discussion started by "b393capt" who titled it "True true wind...":

    http://www.boatbanter.com/showthread.php?t=63554

    Yup, that's Dan in 2005 writing stuff like:

    "I don't understand the reference to the paddlewheel rgnmstr. True wind direction = wind direction (true north) if the boat was anchored at a point on the water, e.g. not relative to the boats movement or water current. To achieve this (with the boat in motion), you need the apparent wind & speed, SOG (from the GPS) and ship heading (true north)
    from your flux gate (COG from GPS introduces error) to get a close approximation, and a little more accuracy can be had if you include adjustments for angle of heel error, heading error (compensate for mast & sail induced air flow), a yaw sensor on the mast, etc ... oh yea, and you need an instrument package that uses this, some like Raymarine wont
    use SOG from the GPS."

    What happened, Dan, some sort of religious conversion?

  • 1. What a really interesting find Ben. Apparently I was brain washed as I became a disciple of the Sailing Wind version of True Wind during my conversion to becoming an arrogant performance sailor (reference Johan). I wonder if it will be considered heresy for me to use the term Sailing Wind? Might there be consequences? Loss of respect in my racing community? No entrance to America Cup racing events?

    Did you see the part in my 2005 thread where I agreed with a commenter writing about terminology that True Wind should be called Wind Relevant to Water ?

    Here, I captured it below

    Another commenter wrote "As a matter of terminology I have never heard anyone use True Wind Speed to be in reference to the moving water, as opposed to a fixed geographic point. While it is true that in a zero wind and a current there will be a wind past the boat, I think that is apparent wind, not true. I don't think that the fact that the wind and water are fluid media moving in different directions makes the wind relative to the water a true wind. I always assumed (and I refuse to do research to back this up) that true wind is the wind that exists at a point if the boat wasn't there. you need a new, even more confusing acronym for that, such as WRTW (wind relevant to water)."

    Dan wrote in response “ -- Yes, right on, WRTW (wind relevant to water) is a great description of the results the ST60”

    2) I kind of like Wind Relative to Water (WRTW), better then Sailing Wind. As far as terminology goes, it sounds more technical, it keeps the TW in the acronym, it is much more likely to get accepted into Wikipedia than Sailing Wind I think.

    3) Clearly there are two definitions of true wind. However, I am still on the fence that Sailing Wind is the answer. Just because I was confused or arguably brain washed, I am not ready to jump on the Sailing Wind bandwagon yet. I want to learn more, for example what is the history of Sailing Wind being called true wind all along, and it nags on me to learn if it is heresy (reference religious conversion) to join an effort to clear up the confusion.

    What would Stan Honey say about True Wind vs. Sailing Wind ?

  • I forgot to add smiles as appropriate above. Please consider them added. Wow, what a find Ben.

  • Dan, it doesn't matter what Stan Honey thinks. He's got much bigger issues (have you seen what the AC72's are doing?) and you have all the facts in front of you anyway.

    "Sailing Wind" works -- and is in use by performance sailors like Mark Chisnell who seem to realize how flawed "True Wind" is -- but I think that Water Wind is better because if references the base point just like Ground Wind does.

    But the bigger question I have is how the heck you have been so adamant about one definition of True Wind and then equally adamant about the other. I can sort of understand the first instance, but both ways? Wow, and you missed the grey, confusing truth both times.

    PS Johan, did you read what Dan used to think about True Wind? Disconcerting, what?

  • Ben, I don't see a religious conversion where a person switches from one God to another.

    I see a sailor, like myself, who wants to learn and understand. And in order to do so discusses true wind in different internet forums. Speaking for myself, it has taken me years to come to a point where I think I understand how different winds interact and how my instruments can be useful. Sailing is an art and learning is a life-long process. So is understanding the wind. If you dig up some old posts I have posted on the internet you will probably find that there have been times when I haven't fully understood everything.

    If I re-read my posts in this thread I see a person who has come to a fairly deep understanding and a who is willing to find ways to explain this to others. I don't see a person who is willing to argue about the term True Wind. I see a person who actually writes that there can be several types of true wind and the important thing is to know the difference between them.

    I understand why people want to call the wind in reference to the ground "true wind" but I feel it is not because it is "true" but because it is "more true" than the other true wind.

    So the real problem is in the word "true". What does "true" mean? How can a mass of air in motion be "true"? True to what? The opposite to "truth" is "lie". What wind is lying?

    What I am saying is that the word "true" should be abandoned altogether. If you describe something that is in motion (in this case a wind) you refer to it as a vector, i.e. with a speed and a direction. This is however not enough as you also need to know in relation to what it is moving. And I think it is rather silly to say that a wind is moving in relation to "Truth". Or is there even a "True Truth" or "Apparent Truth".

    The same with Dead Reckoning. Who died? What did they die from? Cancer? Car accident? Let's rename it "deduced reckoning" to make it clear what it means! (I hope you understand my analogy here.)

    Johan

  • Johan, do you agree that the lines of longitude on your charts and everyone else's charts all point in a very specific direction, True North, to a very specific place, the True North Pole?

    Oh, never mind. I agree that there are two definitions of True Wind and that we boaters should give up both for the sake of clear communications with each other. I like Water Wind and Ground Wind.

    I shouldn't have used a loaded term like religious but the point I was trying to make is that the confusion about True Wind gets magnified whenever someone insists that there is only one proper definition. It becomes a "one true God" situation where a general, fact-based discussion of the subject becomes impossible.

    Precise terminology is very important. Without it, a cartographer couldn't have marked the dangers on your chart so you could avoid them. In the boating world, True Wind has become an imprecise term. That's a fact, and it's the first thing any boater should acknowledge when discussing True Wind. Let's improve our language and use precise terms instead of True Wind.

  • Ben, I agree that the longitudinal lines all point in the direction of True North.

    I accept that this direction is called True North but I don't see what is so true about it, semantically. It should be called something else.

    "True" is just as bad a choice of word as "dead" is in my example in my previous post.

    True north is just a direction. The direction is determined to be parallel with the Earth's axis. It does not make it true, it does not make it false, it does not make it red, it does not make it blue, it does not make it loud, it does not make it soft etc.

    "True" is just a bad choice of word.

    Johan

  • That's going to be a tough sell, Johan. Did you see the pictures Kris Amundson took of the equinox at the True South Pole, the Sun just going around the horizon as seen from one definitive spot? It seems like a reality all of humanity agrees to.

    http://www.flickr.com/photos/krisamundson/

  • Yes, I enjoyed Kris's pictures. I am a keen photographer myself so I know a good picture when I see one.

    I did not see the Earth's axis sticking out from the pole though. Is it hidden in the ground somehow? I can only imagine the size of the ball bearings at each pole. They must be enormous considering that the Earth continuously spins around day after day. (And yes, now I am being silly.)

    Johan

  • I like what Johan wrote. He put it very elegantly. Always learning. And I am in different circles of people in 2005 vs. 2012 and gravitate towards using their definition.

    In 2005 I had just succeeded in passing a grueling advanced navigation class, only student to pass, and the year before that a brutal coastal cruising class (5 weekends at sea on the pacific ocean), in neither situation was sail trim even discussed.

    In 2006 I owned a boat that used the terms true wind and ground wind in configuration menus and displays. I mastered the configuration. Not until this thread have I been curious how my classic e series calculates ground wind now that I have better sensors than in 2006, that had multiple distortion issues.

    In 2010-2012 I have more local racing trophies than will fit on my wall, not from effort, but being with people who know how to make boats go fast, and sail makers that talk True Wind in every sentence.

    Always learning. And it helps, when their math equations to explain it all.

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