Seatalk - True Wind Speed & True Wind Angle

Discussion and support for the Nmea2Wifi multiplexer - a 2-input Nmea 0183 wifi multiplexer.
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HappyAfloat
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Joined: Mon Jan 13, 2020 8:40 pm

Seatalk - True Wind Speed & True Wind Angle

Post by HappyAfloat » Tue Jan 14, 2020 4:05 pm

Hello Luis,

Thank you for a great product.

Is it possible to calculate and output nmea true wind speed and angle from seatalk input?

Luis Sa
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Posts: 535
Joined: Thu May 04, 2017 4:12 am

Re: Seatalk - True Wind Speed & True Wind Angle

Post by Luis Sa » Tue Jan 14, 2020 5:34 pm

Hello,

Thank you for your post. I have recently wrote here in the forum a complete revision of the SeaTalk1 to Nmea0183 conversion comparing the behaviour between the Multiplexer and the Raymarine E85001 bridge. Here is what I found about wind information.

You ask about True Speed and True Angle. As far as I know the primary sensors for wind data only produce apparent data. In order to produce true data you need to know the speed and the heading of the boat. So True Wind Speed, for example, is evaluated using Speed Through Water (Surface Speed) or SOG (Speed On Ground - from GPS). It is for the device that presents information to the user to evaluate this. In my ST70 instruments that I carry in my boat I can choose if the true wind speed is calculated using the value supplied by the Airmar triducer (paddle wheel to get the speed) or the GPS speed. I found by experience that in spite of having a setting to choose between the two supplementary data, mu Raymarine instruments only like Water Speed to evaluate the the True Wind Speed. In fact when I got my paddle wheel stopped with fouling, I changed the setting to use GPS speed instead. Although the instrument accepted the setting, True Wind Speed was identical to Apparent Wind Speed. So, when the paddle gets fouled, the only thing I can do is to clean it so that it moves again.

So the answer to your question is no!

Regards, Luis

HappyAfloat
Posts: 2
Joined: Mon Jan 13, 2020 8:40 pm

Re: Seatalk - True Wind Speed & True Wind Angle

Post by HappyAfloat » Tue Jan 14, 2020 6:54 pm

Hello Luis,

Further info.

I am using the nke display app to provide a repeater at the chart table. The app displays the apparent wind angle and speed fine but not the true wind or angle. I think the app is expecting a nmea WMV sentence with the 't'rue option.

I assume that at the point your code converts the seatalk relative wind speed and angle it would be possible to generate the true wind speed and angle?

Luis Sa
Site Admin
Posts: 535
Joined: Thu May 04, 2017 4:12 am

Re: Seatalk - True Wind Speed & True Wind Angle

Post by Luis Sa » Tue Jan 14, 2020 9:17 pm

Hello,

You refer to MWV. Yes it would be possible but the multiplexer sends out the apparent data, heading and water speed when the the corresponding Seatalk1 datagrams arrive. It is for the receiving device to combine that data. I am afraid that the multiplexer processing capacity can be compromised if I transpose those functions to the multiplexer. Nevertheless I could experiment this possibility but only next February.

Regards Luis

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