Raymarine ST40 Wind not listening to Garmin GPS :-(

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.
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"Kees Verruijt" <kees DeleteThis @scanner391.net> wrote in message
news:425543f0$0$149$e4fe514c@news.xs4all.nl...
> 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
 >> Stay informed about: Raymarine ST40 Wind not listening to Garmin GPS :-( 

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.
 >> Stay informed about: Raymarine ST40 Wind not listening to Garmin GPS :-( 

That appears to be the case. I have the same bridge set-up except with ST-50
Wind. When I was designing it, I became concerned about data sentence
conflicts with Seatalk, converted Seatalk and NMEA all running on the same
buss. And, like you, I was curious about whether it was possible to use GPS
SOG rather than boat speed. One chap who seemed to know a lot about this
indicated that in case of conflict, Seatalk prevails. So it seems that if
boat speed is available in Seatalk, your instrument will ignore other data.
Additionally, as far as I know, Seatalk format speed is the required input
for that instrument. So short of some programming to fake it (convert NMEA
to Seatalk), I don't think there's a workaround. I wasn't willing to go that
route, and it had the shortcomings descibed in other posts.
Len


> 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.
..
 >> Stay informed about: Raymarine ST40 Wind not listening to Garmin GPS :-(