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gadgetPool.de :: View topic - SeaTalk-NNMEA-Bridge : True Wind direction SOG/STW
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SeaTalk-NNMEA-Bridge : True Wind direction SOG/STW

 
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FWallenwein
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PostPosted: Thu May 04, 2006 10:13 am    Post subject: SeaTalk-NNMEA-Bridge : True Wind direction SOG/STW Reply with quote

Calculating true wind direction and true wind speed from apparent wind direction/speed and boat speed.


The wind instruments on the boat can - of course - only meassure apparent wind direction and apparent wind speed.

To calculate true wind direction/speed, the instrument needs to know the boat speed.

Our wind instruments use STW ( speed through water ) for this calcualtion.

This is fine, as long as you have a STW transducer and instrument,
and as long as you want to know true wind direction/speed relative to water.

Your Instrument will show you true wind speed - the speed the wind has, when your boat is not moving through the water. So, when you turn off your engine, take down all the sails - than youl'll fell exactly the windspeed, that you instrument showed you as "true windspeed".

Great - so far.
But what if we are sailing in tidal waters or even in a river ?
And what if we would like to know the "true windspeed/direction" as speed/direction relative to the ground, relative to land or when we are anchoring ? Sometimes this is called ground wind

If we want to see that ground wind we have to take SOG ( speed over ground ) instead of STW to calculate wind speed and direction.

There are some wind instrument types where you can select if you want to use STW or SOG for the calcualtions.

One user reported, that a ST60 and ST40 Wind instument can not deal with speed-over-ground data. It always wants to "see" speed through water.

If you only have a GPS and a ST60-Wind than you don't have speed-through-water but only speed-over-ground.

I made a special option, where NMEA input speed-over-ground is sent to SeaTalk output as speed-through-water.

The ST60-Wind now thinks we have speed-through-water and can calculate true windspeed and true heading.
It actually gets the SOG values, but it thinks it had STW and calculates true speed/direction with this values.

So what you get is true windspeed/winddirection not relative to water but realtive to ground.

When you're sailing in strong currents or on rivers this function allows you to get "real" true wind direction from your ST60/St40 wind instrument.

This functions has been tested on two boats.

Switch on STW=SOG : $SNBSE,14,0
Switch off STW=SOG : $SNBSE,14,1


Last edited by FWallenwein on Tue Jun 03, 2014 9:19 pm; edited 1 time in total
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FWallenwein
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PostPosted: Mon Mar 19, 2012 3:42 pm    Post subject: Reply with quote

Very Happy Welcome !

Meanwhile we have used this function on several boats.
Mainly it is used by boaters who have a GPS but no water-speed transducer.
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ribw
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PostPosted: Wed Apr 30, 2014 11:56 am    Post subject: Artificial Boat Speed OK but why 0kn? Reply with quote

I installed the Converter over the winter and my ST60Wind indicated 'True' wind - previously it would automatically revert to 'App'. I moved the boat for the first time yesterday. SOG is derived from a Garmin 128. My slave ST60 Speed (x2) showed SOG converted from the Garmin128 but 'Boat Kts' never showed anything other than 0.0.

So the converter is seeing the correct SOG input and converting it to ST.
The converter is producing 'Boat Speed' because it is fooloing the ST60 wind.

Before I tie my brain in knots (pse forgive pun), has anyone ant thoughts as to why the value of SOG isn't being converted?

Regards
Bob
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FWallenwein
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PostPosted: Wed Apr 30, 2014 2:03 pm    Post subject: Re: Artificial Boat Speed OK but why 0kn? Reply with quote

ribw wrote:
My slave ST60 Speed (x2) showed SOG converted from the Garmin128 but 'Boat Kts' never showed anything other than 0.0.


Hi Bob,
not sure I fully understand.
    That second ST60 Speed, does it get SOG from the Garmin ? Does it habe an NMEA In-Port or is it getting its data from SeaTalk ?


Bets regards
Frank
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FWallenwein
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PostPosted: Wed Apr 30, 2014 2:26 pm    Post subject: Reply with quote

Hi again,

I asume there is no transducer connected to the second ST60 ? Right.
You could check if its in "Repeater mode".
- Press Speed & Trip Key for approx 4 seconds.
- Display shows Software Version.
- Press "Speed"
- Instrument shows "Repeater" od "Master"

Hole Speed & Trip for approx 2 seconds to go back to normal operation mode.

Frank
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ribw
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PostPosted: Wed Apr 30, 2014 3:29 pm    Post subject: Reply with quote

Hello Frank - your speedy response is much appreciated!

I had disconnected the transducer (paddlewheel) to the original 'master' ST60 of the pair, but I made no configuration change to direct the ex-master to be a slave. I was led to believe that disconnecting the paddle wheel automatically made the unit a slave - I will double check this.

The second ST60 speed has always been a slave.

There is no NMEA connection to either of the ST60speed. They are connected together and to the converter using ST only

And yes, the only source of SOG was the Garmin.

I will check the status of the ex-master ST60speed next time I am on board (She went in to the boatyard for at least two weeks yesterday).

In case I wasn't clear in my original posting, The ST60wind now holds in true mode but must also be receiving Boat Speed = 0.0kts because direction and wind speed do not alter when switching between True & App.
Thanks for your advice.
Best Regards
Bob
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FWallenwein
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PostPosted: Wed Apr 30, 2014 5:13 pm    Post subject: Reply with quote

All right -

what I understood.
You have :

- A Garmin GPS sending data to the SeaTalk NMEA Bridge
- The SeaTalk side of the Bridge is connected to the SeaTalk Bus
- On this bus you have ST60 Speed, ST60 Speed, ST60 Wind
- Both ST60 Speed do not have a transducer attached.

On the SeaTalk Nmea Bridge, you have set $SNBSE,14,0.
This enables sending SOG the SeaTalk as SOG and STW.

Well - this should work....
I have pretty much the same configuration here
( Garmin GPS, Bridge, ST40 Wind, ST80 Masterview )
and it works.



SOG display is correct
STW is shown as 0

I wonder where this STW 0.0 comes from.
If one of the ST60 Speed would still send its STW, than your ST60 Wind should show "True" even without the bridge.
But you said, without the bridge, the ST60 Wind switches back to 'App'.
Strange.

I also believe that disconnection the transducer does set the device to "slave mode". But I'm not sure.

If it does not, it would explain the 0.0 STW:
The ST60 Speed would send 0.0 - because the transducer sends 'nothing'.
The Bridge would see 'some other device is already sending STW data', and this would stop the bridge from sending its own STW data.

Looking forward to hear the results of your check on the boat.

Best regards
Frank
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ribw
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PostPosted: Wed Apr 30, 2014 8:02 pm    Post subject: Reply with quote

Thanks Frank.

Yes you understand correctly about the configuration.

I am very grateful for your thoughts. I will dig deeper in the next couple of weeks and do some more physical disconnects/connects when I have the boat back on the water - hopefully 2 to 3 weeks time.

At least, I am now able to see SOG on my ST60s - a great step forward! Getting the ST60 to give a reasonable 'True' wind will be the 'icing on the cake'.

I'll update you when I learn more.

Best Regards
Bob
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ribw
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PostPosted: Tue Jun 03, 2014 5:21 pm    Post subject: Reply with quote

ribw wrote:
Thanks Frank.

Getting the ST60 to give a reasonable 'True' wind will be the 'icing on the cake'.

I'll update you when I learn more.
Bob


Frank,
I had left the two wires which sense water temperature connected to the saloon display. Reading up on the device, I ffind that these two wires dictate that the display is designated as the 'master'.
After I disconnected the pair and restarted the instruments, the 'Boat Speed' correctly displayed SOG and the true wind speed was indicating as it should. My cake has been 'iced' .
Thanks very much for your help
Regards
Bob
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FWallenwein
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PostPosted: Tue Jun 03, 2014 6:29 pm    Post subject: Reply with quote

Hi Bob,

thank you for your update.
Well - learned something again.
I had no idea, that it's the water temperature sensor, that switches between master and slave.
This is valuable information to other users as well.

Thank's again
Regards
Frank
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emmegi
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PostPosted: Wed Jan 25, 2017 5:34 pm    Post subject: SOG ST60 tridata Reply with quote

Hi Frank,
I want use the bridge to take the SOG from GPS and send it as STW to ST60 Tridata.
From your post I've understood that in this case the ST60 must be set as slave, but, it's a tridata so I need it for the depth, Do you know if it can be slave only for the speed but not for depth?

Thanks
mg
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FWallenwein
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PostPosted: Wed Jan 25, 2017 7:37 pm    Post subject: Reply with quote

Honestly - I have no idea.
I guess I simply would try to leave the depth transducer connected, disconnect the speed transducer and see what it shows when you send STW from the bridge.

Not sure if it works though.

Cheers
Frank
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