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 is talking happily to my ST1000+ AutoHelm, and the AutoHelm is
also receiving track data from the GPS (directly, not through the
E85001), so it seems only the ST40 Wind doesn't want to play ball :-(

I've tried contacting Raymarine but it's been nearly two weeks now, and
they still haven't replied to my query, though I live in hope.

Anyone got any ideas what might be going on?

Who.

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 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

Kees Verruijt wrote:


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

I did fear this was the case. Why do they make the distinction? Surely
if one is not available, but the other is, it could use boat speed over
ground to make the same computation.


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

You're right, I didn't want to hear this, as I know no way of making my
GPS output speed over water, rather than speed over ground, and non GPS
based speed/log information is affected by tidal flows, etc.


-- Kees

Thanks for you reply.

Who.

"Who Me" wrote in message
...
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 is talking happily to my ST1000+ AutoHelm, and the AutoHelm is
also receiving track data from the GPS (directly, not through the E85001),
so it seems only the ST40 Wind doesn't want to play ball :-(

I've tried contacting Raymarine but it's been nearly two weeks now, and
they still haven't replied to my query, though I live in hope.

Anyone got any ideas what might be going on?

Who.

I've tried contacting Raymarine but it's been nearly two weeks now, and
they still haven't replied to my query, though I live in hope.

Did you send a note to technical assistance from their web page? I sent
them a note yesterday asking if GPS waypoint data would be picked up by
Seatalk and then tranlsated back to NMEA format by the E85001 and they
phoned me today with an answer. (unfortunately the answer is no and therefor
I must run a separate wire from my GPS to my radar). I was put in touch
with

Winston Savage
Technical Support Specialist
Rayamrine Inc.
http://www.raymarine.com

at

Gordon Wedman wrote:


I've tried contacting Raymarine but it's been nearly two weeks now, and

they still haven't replied to my query, though I live in hope.

Did you send a note to technical assistance from their web page? I sent

Yes, using their online form. It sent me an email, and the question is
still there on their website where I can update it, add files, etc.
They promised to get back to me within three business days but apart
from the initial email, I've heard nothing.

them a note yesterday asking if GPS waypoint data would be picked up by
Seatalk and then tranlsated back to NMEA format by the E85001 and they
phoned me today with an answer. (unfortunately the answer is no and therefor

I'm in Australia so I don't really expect them to ring me :-) We do
have email down here though, so I was hoping to hear something from them
that way, even if the answer is no.

Unfortunately, I think I've received my answer from the other posters in
here - I need to go outside the Raymarine stable to solve the problem by
changing boat speed over ground into boat speed over water :-( I should
have bought a different NMEA - Seatalk bridge that could do the data
manipulation for me instead of the E85001.


Winston Savage
Technical Support Specialist
Rayamrine Inc.
http://www.raymarine.com

at


Thanks for that. If I need more help, I may use it.

Who.

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.

On Fri, 08 Apr 2005 07:17:11 +1000, Who Me
wrote:

Kees Verruijt wrote:


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

I did fear this was the case. Why do they make the distinction? Surely
if one is not available, but the other is, it could use boat speed over
ground to make the same computation.


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

You're right, I didn't want to hear this, as I know no way of making my
GPS output speed over water, rather than speed over ground, and non GPS
based speed/log information is affected by tidal flows, etc.

The usual reason for the true wind calculation is to let you know
where the wind will be after the next mark rounding. You want the true
wind relative to the water for this purpose, and that is why the
instruments use the signals they do.

You could certainly retag the gps word to simulate a log, but the
result is only equivalent when there is no current.

The calculation is extremely sensitive to wind speed and boat speed
calibration, which is difficult to do well enough to make sensible
results where I live (NYC). There is never a total slack long enough.



Rodney Myrvaagnes NYC J36 Gjo/a


"Nuke the gay whales for Jesus" -- anon T-shirt