"Kees Verruijt" wrote in message
...
Who Me wrote:
I am trying to get True Wind from my ST40 Wind instrument.

I am using a Raymarine E85001 SeaTalk/NMEA converter box to take the
NMEA 0183 output from my Garmin GPSMAP175 GPS and send it to the ST40
Wind.

Connecting a PC to the RS232 terminals of the E85001 shows that both
instruments are talking to the E85001, but the ST40 Wind still does not
compute true wind. The GPS is sending NMEA sentences VTG and RMC which
both have boat speed information in them, so I don't understand why the
ST40 won't use it. I've tried choosing different NMEA output settings
on the GPS, and the sentences change slightly, but the ST40 still
ignores the boat speed info.

The ST40 computes true wind angle/speed when it knows speed thru water,
not when it knows speed over ground.

The solution is simple (but probably not what you want to hear): install
an STx0 speed/log instrument.

-- Kees

Kees is right, the wind instrument needs speed through the water. However,
speed over the ground would actually give you a more accurate true wind
speed/angle, as current does not affect it. There are 2 other alternatives:
1. The Navman wind instrument accepts GPS SOG for true wind calculation.
2. With a (standard) Brookhouse NMEA multiplexer, you can "convert" the GPS
speed data to (faked) speed through the water (VHW sentence), with a simple
script that is loaded into the multiplexer. Feed the mux output into your
E85001 and your wind instrument is happy.
Option 2 is the cheapest and gives you a lot of other functions as well,
which may be useful for future use. I'm biased, of course :-).
Wout

Wout B wrote:

Kees is right, the wind instrument needs speed through the water. However,
speed over the ground would actually give you a more accurate true wind
speed/angle, as current does not affect it. There are 2 other alternatives:

Thanks, that is my opinion as well. The only introduced error using SOG
is when the boat's movement has a sideways component, since the
wind instrument will assume that all the boat's motion is forward, and
calculate a slightly wrong true wind speed & direction. I think this is
likely to be a smaller error (certainly in the areas I sail) than that
introduced by currents, and it can only be removed with a complex vector
subtraction - I wonder if anybody bothers to do this?

1. The Navman wind instrument accepts GPS SOG for true wind calculation.

One wind instrument is enough, thanks, especially since it talks nicely
to my AutoHelm :-)

2. With a (standard) Brookhouse NMEA multiplexer, you can "convert" the GPS
speed data to (faked) speed through the water (VHW sentence), with a simple
script that is loaded into the multiplexer. Feed the mux output into your
E85001 and your wind instrument is happy.

This is more interesting. At first I thought it would remove the need
for the E85001, but it doesn't appear to output SeaTalk, so I haven't
completely wasted my money on the E85001 :-)

I checked out your website, but didn't see any instructions regarding
the "simple script" you mention. Can I assume that this kind of
information would come with the unit if I order one? I am thinking of
the one with USB connection as well.

Option 2 is the cheapest and gives you a lot of other functions as well,
which may be useful for future use. I'm biased, of course :-).

Thank you, and thanks for being honest about your bias. Buying such a
unit will save me having to do it myself (if I could even remember how
to program a microcontroller - it's been many years!) :-)

Who.

"Who Me" wrote in message
...
Wout B wrote:

Kees is right, the wind instrument needs speed through the water.
However,
speed over the ground would actually give you a more accurate true wind
speed/angle, as current does not affect it. There are 2 other
alternatives:

Thanks, that is my opinion as well. The only introduced error using SOG
is when the boat's movement has a sideways component, since the
wind instrument will assume that all the boat's motion is forward, and
calculate a slightly wrong true wind speed & direction. I think this is
likely to be a smaller error (certainly in the areas I sail) than that
introduced by currents, and it can only be removed with a complex vector
subtraction - I wonder if anybody bothers to do this?

1. The Navman wind instrument accepts GPS SOG for true wind calculation.

One wind instrument is enough, thanks, especially since it talks nicely
to my AutoHelm :-)

2. With a (standard) Brookhouse NMEA multiplexer, you can "convert" the
GPS
speed data to (faked) speed through the water (VHW sentence), with a
simple
script that is loaded into the multiplexer. Feed the mux output into
your
E85001 and your wind instrument is happy.

This is more interesting. At first I thought it would remove the need
for the E85001, but it doesn't appear to output SeaTalk, so I haven't
completely wasted my money on the E85001 :-)

Nono


I checked out your website, but didn't see any instructions regarding
the "simple script" you mention. Can I assume that this kind of
information would come with the unit if I order one? I am thinking of
the one with USB connection as well.

Who(ever),
It is there, under "Click here for more information" where the
filtering/editing function is described. Here is the link anyway:
http://brookhouseonline.com/pdf%20fi...%20Editing.pdf

Following is the script that "converts" the RMC sentence from the GPS into a
VHW sentence:

*S,2,GPRMC,VWVHW
*D,2,GPRMC,1
*D,2,GPRMC,2
*D,2,GPRMC,3
*D,2,GPRMC,4
*R,2,GPRMC,5
*R,2,GPRMC,6
*I,2,GPRMC,8,N
*D,2,GPRMC,8
*D,2,GPRMC,9
*R,2,GPRMC,10
*R,2,GPRMC,11
*E

You (and anyone else interested) can copy and paste it into Notebook, save
it and upload the .txt file to the multiplexer, after you got one :-)

Here is the result:
Original GPS sentence:

$GPRMC,145306.79,A,0214.64149,S,13726.27309,E,5.0, 315.0,080405,5.0,W*55

Becomes (produced by mux):

$VWVHW,,,,,5.0,N,,*2D

So 5.0 knots speed over the ground has become 5.0 knots speed through the
water.
With this, who wants (an always fouling) speed instrument anymore?

Now, if you also want to send the mux output to a laptop, AP or repeater
instrument, of course you don't want to lose the original RMC sentence. The
above script converts the RMC received via channel 2. If you connect your
GPS to e.g. channel 1 and 2, the RMC on channel 1 remains unaltered. Use the
*W directive in the script to suppress any double sentences.

I hope this helps.
Wout


Option 2 is the cheapest and gives you a lot of other functions as well,
which may be useful for future use. I'm biased, of course :-).

Thank you, and thanks for being honest about your bias. Buying such a
unit will save me having to do it myself (if I could even remember how
to program a microcontroller - it's been many years!) :-)

Who.

Wout B wrote:

I checked out your website, but didn't see any instructions regarding
the "simple script" you mention. Can I assume that this kind of
information would come with the unit if I order one? I am thinking of
the one with USB connection as well.


Who(ever),
It is there, under "Click here for more information" where the
filtering/editing function is described. Here is the link anyway:
http://brookhouseonline.com/pdf%20fi...%20Editing.pdf

Thanks for the link - my mistake :-)


Following is the script that "converts" the RMC sentence from the GPS into a
VHW sentence:

*S,2,GPRMC,VWVHW
*D,2,GPRMC,1
*D,2,GPRMC,2
*D,2,GPRMC,3
*D,2,GPRMC,4
*R,2,GPRMC,5
*R,2,GPRMC,6
*I,2,GPRMC,8,N
*D,2,GPRMC,8
*D,2,GPRMC,9
*R,2,GPRMC,10
*R,2,GPRMC,11
*E

You (and anyone else interested) can copy and paste it into Notebook, save
it and upload the .txt file to the multiplexer, after you got one :-)

Thank you, order placed via Paypal :-) I think we get airmail delivered
to Australia, but maybe the planes only arrive once per week . . .


Here is the result:
Original GPS sentence:

$GPRMC,145306.79,A,0214.64149,S,13726.27309,E,5.0, 315.0,080405,5.0,W*55

Becomes (produced by mux):

$VWVHW,,,,,5.0,N,,*2D

So 5.0 knots speed over the ground has become 5.0 knots speed through the
water.
With this, who wants (an always fouling) speed instrument anymore?

Very nice.


Now, if you also want to send the mux output to a laptop, AP or repeater
instrument, of course you don't want to lose the original RMC sentence. The
above script converts the RMC received via channel 2. If you connect your
GPS to e.g. channel 1 and 2, the RMC on channel 1 remains unaltered. Use the
*W directive in the script to suppress any double sentences.

Very clever, thanks.


I hope this helps.

I'm sure it will.

Thanks again,

Who.