True vs Apparent Wind Speed

SV_Atlas

Hello!

We have recently installed Saillogger on SignalK and are enjoying having a good tracker for our family back home.

I've noticed that the wind speed is Apparent, while wind direction is True. I would like to have the wind speed as True but when I make the change "environment.wind.speedTrue" I no longer have any wind data on our tracking page. If I change it back to "environment.wind.speedApparent" then the wind data reappears.

I have installed Derived Data but that has not solved the problem.

My only thought is that it appears Derived Data needs to have some sort of boat speed for it to derive the true wind speed. Is this correct? If so, I believe, then, that if we are anchor and the wind speed is set to True, then it will display a value of 0 until we move again.

Can you confirm if this is correct?

If so, may I suggest that there is both an Apparent and True Wind speed?

Thank you very much for building what appears to be a really great product.

admin

Hi there,

For true wind speed and direction, you should toggle the following option on in the derived-data plugin:

True Wind Angle, Direction and Speed

In order to calculate true wind values, the following are required:

navigation.headingTrue
navigation.speedThroughWater
environment.wind.speedApparent
environment.wind.angleApparent

speedThroughWater should be coming from your speedometer, and when anchored, it will be zero, so no problems there. speedApparent and angleApparent come through wind instrument and should be fine too.

headingTrue is the tricky one, it normally comes through the heading sensor which is normally linked to autopilot but depending on your instruments, it may be sourced from elsewhere too. If you don't have all of these, derived-data will not be able to calculate the true wind readings.

You can see which ones are available in the data browser.

Good luck and happy Saillogging!

SV_Atlas

Done! Thank you very much. That was an easy fix and simply required power to my course computer.

SV_Atlas

This post is deleted!

ilederey

Hello

I'm trying to have the real wind and true wind direction data but I don't know how to do it!!!

I installed the derived data plugin but after?.

Thank you for your help

admin

Hi @ilederey , there are two distinct things here.

Having true wind in Signal K. This will depend on a few things, your instruments might already be putting it out into NMEA, if so, it should automatically propagate to Signal K. You can see this in Signal K data browser as environment.wind.directionTrue. If your instruments don't automatically provide it, then you can use derived-data plugin. Install the plugin and toggle on True Wind Direction and True Wind Angle under Wind section. Note that these will require navigation.headingTrue among other things. Check if you have that available, if not you can calculate it from navigation.headingMagnetic but it will require a heading sensor (likely an autopilot) and navigation.magneticVariation, which derived-data can provide.
Regardless of the source, once you have environment.wind.directionTrue in Signal K, you can then add a custom monitoring section in Saillogger to monitor it. Details of it is covered in this tutorial.

Good luck!

ilederey

Thank you for your answer

My Garmin system only gives me the apparent wind!
So I installed the dérived-data plugin but how to activate True Wind Direction and True Wind Angle under Wind section? Nothing has changed the plugin!

Thanks

admin

You need to do it in plugin configuration, normally accessible at http://venus.local:3000/admin/#/serverConfiguration/plugins/derived-data when you are on the same network with Cerbo.

ilederey

OK thank you it's work perfectly !!! Very nice ...

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True vs Apparent Wind Speed