Correcting Wind and STW for vessel motion?

[rgleason]

The wind indicator is on a long arm (mast height + wand) waving around changing the wind data vectors and magnitude. This data is used for sailing to the wind and thus it can dramatically affect an autopilot.

I am told that the B&G H5000 Computer corrects wind with vessel motion data (pitch and yaw). It appears (not confirmed) that the newer B&G NAC and the Raymarine EV may only be using the newer more accurate compasses for heading information only and that "pitch and yaw" and the PGN 12725 are not being used to compensate (wind speed and direction, and speed through the water (STW) for vessel motion.

I can really understand how bad yaw in waves would screw up wind data (same for STW to a lesser degree). Pitch is not quite as much of a factor, but it would still affect the vectors and magnitude for both instruments.

I realize that there is a latency or concurrency problem in correcting wind (and STW) because the separate ships compass sensor sends data at a certain interval and the wind instrument sends it at a different time. What is needed is a wind instrument with an accurate compass that has pitch and yaw, and that data is processed in the wind instrument itself instantaneously so that the wind data being sent is corrected for vessel motion (same for STW).

Steve Adler has been very helpful in various threads, trying explain sort this question out, as have others. I thought it would be helpful to have a discussion in this forum.

1. Is it possible to use a separate 20mhz Precision Compass to correct wind data from a separate instrument? (IE is latency or delay an issue?)
2. If it is possible to make this correction using compass (pitch and yaw) data from a separate instrument than the wind instrument, how would the data be handled in a Nmea2000 or Nmea0183 (probably too slow) network? There would be different versions of wind data being sent around!
3. Does anyone know more about the B&G Triton2/NAC and Raymarine EVO autopilot computers with respect to this issue?
4. How does pypilot address correction of wind and STW for vessel motion?
5. How would you do this?
6. How does an accelerometer instrument differ from compass pitch and yaw?
7. Is an accelerometer a better way to make corrections to wind and STW for Vessel motion?

[Dockhead]

There's a guy on here who posts as "Christer" who is a profound expert on these questions. I hope he'll show up and give an opinion.


I know only a little but will share what I know:


1. The conventional method of dealing with this is DAMPING.

2. The H5000 corrects wind data for boat motion using the H5000 motion sensor, which gives RATES, not the different PGN for attitude. That's also an answer to your question no. 6.
3. The latency in wind measurements is a crucial question and NMEA0183 or pulse, wired directly to the H5000, is required for really good performance. N2K has a lot more latency depending on the bus load. I am debating trading in my SCX20, which is N2K, for an SCX21, which is 0183 and can be wired directly to the computer.
4. In order to use corrected wind data on an N2K network, you need for the device making the correction to be set as the source. The H5000 can correct data provided over N2K; you just set the H5000 as the source if you want the corrected data rather than the raw output from the sensor.
5. N2K speed logs work poorly in my experience. I have had two versions of the exact same ultrasonic speed log -- the CS4500 (pulse) and the UST850 (N2K). The CS4500 was vastly superior.

6. I don't believe any of the pilot computers can do these corrections -- you can't set them as a source for Apparent Wind.


Hope that's helpful. I will be following this discussion.