Please excuse a newbie who is struggling to figure out exactly how these things work.
I want to keep my totally reliable old VDO wind masthead units and have found that the only NMEA 0183 sentence that the VDO wind instrument puts out that can be translated to NMEA 2000 by the Actisense NGW1 Gateway is VWR, which is relative (i.e. apparent) wind speed and direction. (I can keep the old instrument connected, and hide it out of sight when its LCD fails)
Am I right in thinking that if I keep the VDO wind instrument and connect its NMEA0183 output to the gateway the display instruments themselves will calculate the true wind speed and direction from the relative wind speed and angle data plus the inputs from the log and/or GPS? Does it work that way, or is the calculation of true wind data performed within NMEA 2000 mast head units rather than in the display instruments?
I already have a Garmin GMI 10 display but want to add B&G Tritons at both helms.
As an aside the VDO instruments in my old system all talk to one another via their own CANBUS logic bus, but I can find no information at all about linking this with NMEA 2000.
Norman,
The NMEA 2000 specification does not say who calculates the true wind. In fact in my Simrad-mostly network this calculation is done not by the IS-20 wind sensor nor any of the displays but by the AC-42 autopilot computer.
My Airmar PB200 sends out true and apparent wind directly, but that makes sense as it has a built-in compass.
I can check next week if the Triton comes up with true wind if it sees the necessary components on the network but not the true wind data, but this will take some unplugging and I don't have the time right now.
Very reasonable question, Norman! This is a somewhat confusing part of NMEA 2000 (like magnetic variation) but I'm pretty sure that the GMI 10 and Triton can calculate True Wind if they're getting Apparent angle and speed and either boat speed or SOG (and you get to choose if both "speeds" are available). They'll also display Ground Wind if they have heading data. I couldn't find the Triton manuals at B and G but did find links here, and True calculation is mentioned:
http://www.wmjmarine.com/c43513.html
What a helpful forum this is. Thank you both. I too had struggled to find online B&G manuals, and Ben's link above has solved that problem. I did put my query to B&G and the answer that I have from them indicates that they have not tried what I am proposing and cannot confirm that it would work, though they did say that NMEA0183 data such as GPS data fed though an 0183/2000 gateway does work.
Kees, if you can make the check that you suggested, I think that will solve the issue, and I will go ahead and buy the Actisense gateway.
Norman,
I just checked and I can confirm that the B&G Triton will show true wind with only a heading and wind sensor in the network.
Thank you very much. I am just about to buy the rest of the NMEA 2000 kit and will probably buy a complete set of instruments including a mast head unit because that is the cheapest way to go, but I will also get the Actisense Gateway and install that, just keeping the new NMEA2000 MHU wrapped up safely for when it is needed.
Really ?? True wind with only a heading and wind sensor? How does it do it without a speed thru water sensor?
See this reference:
https://www.panbo.com/archives/2009/10/airmar_cs4500_part_ii_reliable_true_wind.html
Aargh,
Sorry of course I meant speed and wind sensors, not heading and wind.
"My Airmar PB200 sends out true and apparent wind directly, but that makes sense as it has a built-in compass."
Just so I can consolidate this info, then the PB200 would be getting STW from the n2k network? Does the PB200 supply ground wind as well and is it true or magnetic?
Thanks.
I checked again and it looks as if my PB200 doesn't send out "true-referenced-to-boat" at all. it sends out apparent wind and ground wind. It doesn't seem to use the available speed-through-water on the network.
I analysed a log with the proper full set of sensors (compass, wind, GPS) and non-null boat speed the reported data is:
PB200 apparent wind every 500ms:
130306 Wind Data: 6E 34 01 D7 E3 FA FF FF
130306 Wind Data: SID = 110; Wind Speed = 3.08 m/s; Wind Angle = 334.2 deg; Reference = Apparent
About 300 ms after the apparent wind it sends out ground wind:
130306 Wind Data: 6D 9F 00 18 C8 F8 FF FF
130306 Wind Data: SID = 109; Wind Speed = 1.59 m/s; Wind Angle = 293.5 deg; Reference = True (ground referenced to North)
My IS20 wind wand sends apparent wind every 100 ms (10 / s):
130306 Wind Data: FF 5E 01 B7 CE FA FF FF
130306 Wind Data: Wind Speed = 3.50 m/s; Wind Angle = 303.2 deg; Reference = Apparent
My AC42 autopilot computer receives heading, speed through water and the apparent wind and then sends out true wind boat referenced every 200ms:
130306 Wind Data: FF 24 01 FA B1 FB FF FF
130306 Wind Data: Wind Speed = 2.92 m/s; Wind Angle = 261.1 deg; Reference = True (boat referenced)
And every 500ms it sends out ground wind:
130306 Wind Data: FF 24 01 D8 BB F8 FF FF
130306 Wind Data: Wind Speed = 2.92 m/s; Wind Angle = 275.5 deg; Reference = True (ground referenced to North)
The above data is all from about the same time, if you want to recalculate what they are doing here are GPS, heading and boat paddle wheel sensor data:
(GPS data from PB200:)
129026 COG & SOG, Rapid Update: 12 FC 22 0C F6 00 FF FF
129026 COG & SOG, Rapid Update: SID = 18; COG Reference = True; COG = 17.8 deg; SOG = 2.46 m/s
(Heading from PB200:)
127250 Vessel Heading: CF 2E 08 00 00 00 00 FD
127250 Vessel Heading: SID = 207; Heading = 12.0 deg; Deviation = 0.0 deg; Variation = 0.0 deg; Reference = Magnetic
(Heading from RC42:)
127250 Vessel Heading: FF BE 09 FF 7F FF 7F FD
127250 Vessel Heading: Heading = 14.3 deg; Reference = Magnetic
(Speed from Airmar DST200:)
128259 Speed: 1C D5 00 FF FF FF FF FF
128529 Speed: SID = 28; Speed Water Referenced = 2.13 m/s
So far so Good!
I have installed & connected the NMEA2000 network and the Actisense Gateway, and the new instruments are displaying Apparent wind speed & direction. I cannot yet check True windspeed & direction because the boat is on the hard and I cannot spin the log paddlewheel and see the instruments at the same time, but I have no reason to believe that it will not work. I even had a real victory with the old VDO wind instrument which had a very worn case, screen and keys, as I was able to dismantle it and put the works into a much better case with good keys.
IT WORKS!
Once I was able to test it, with someone spinning the log impeller it was clear that it is all OK.
I know this is an old thread but I'm a little confused about something.
How is it that you are able to get TRUE wind speed using the speed log? Wouldn't you need speed over ground not speed through water in order to get true wind speed? Any calculations performed using speed through water would not take into account currents.
It confuses lots of people, Chris! The problem is that racing sailors appropriated "True Wind" when they really mean True Wind relative to the water. It's an important value because then you can measure what your boat's optimal performance at different wind speeds and angles regardless of the speed changes current produces.
What meteorologists and many of the rest of us call True Wind is called Ground Wind is sailor world. This nomenclature mess has been discussed a lot on the blog, like here:
https://www.panbo.com/archives/2013/03/the_equinox_celestial_mechanics_pesky_true_wind.html
My system as described above has worked very well. At present true wind is derived from water speed as well as apparent wind speed and direction, but I can change it to use SOG. As I sail in non tidal waters where there are only gentle currents I will try it, as water speed measurement from the paddlewheel tends to under-read at low speeds and over-read once speed rises above 6 knots.
Thanks for the clarification. Makes sense now.
Hi everybody,
Does anyone know if B&G Triton can accept speed and heading data from my NMEA 2000 GARMIN GPS (ground speed) in order to calculate true wind? Thank you in advance.
That shouldn't be a problem, Christos, but be aware that "True Wind" is a vague concept. For most sailors, especially racers, it's simply Apparent Wind Speed and Direction minus boat Speed Thru the Water relative to your bow. The SOG and COG (not Heading) that GPS can measure have nothing to do with it (though many current instruments like the Triton will let you use SOG instead of STW).
More here and elsewhere on Panbo:
https://www.panbo.com/archives/2013/03/the_equinox_celestial_mechanics_pesky_true_wind.html
Christos, Ben is right, and I can confirm that there is no problem with hardware compatability over different makes as I have a Garmin NMEA2000 GPS on my system with Triton instruments, an Airmar log/depth, and apparent wind data actually supplied from a very old VDO instrument via an Actisense NMEA0183 to 2000 gateway. I normally have true wind calculated from the log, but have tried it using COG & SOG, and it works.
Thank you Ben, very nice article. I want to use SOG from GPS and AWD from Triton, as I will not have a speed meter sensor until I dry-dock my boat.
Thanks again.
Ben, I replied to thank you the next day, but somehow something went wrong. Thanks anyway, nice article. When I install Triton, I will post the results.
I installed it an it works fine. N2k is the definition of plug-n-play! I can see any info I want on both instruments with very little customization. I hope that the manifacturers will stick to this protocol.