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Old 29-05-2011, 07:35   #1
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Nav System Question for Electronics Whizzes

I have had a problem with displayed heading data since I bought my boat two years ago. I have an older Raymarine nav system with RL80CRC+ and RL70RC+ MFD's, and the other usual Raymarine stuff of that era. Heading data comes from a Raymarine fluxgate compass, and the data is obviously good since it is accurately dislayed on the Ray ST7000+ pilot head, and the autopilot works very well.

The fluxgate is connected to the S3 autopilot corepack, and heading data is sent from there to the RL80CRC+ via Seatalk. I have not replaced that cable, but I have retrimmed the ends and reset them.

I have recently been given advice by a marine electronics guy in Cowes that I should simply connect the corepack to the RL80CRC+ via NMEA083. Sure enough, the corepack has NMEA output terminals, and sure enough -- I have a free pair of NMEA input terminals via the RL80CRC+'s power cable. This guy -- against his own interest, as I was offering to pay him to investigate the problem -- told me to just hook it up. He said NMEA heading data has a much higher refresh rate than Seatalk, and that the system would automatically prefer NMEA heading data to Seatalk heading data, and that since I obviously have good heading data in the system, this should solve my problem.

It sounds absolutely logical to me -- anybody have any thoughts before I dive in?
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Old 29-05-2011, 09:17   #2
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Re: Nav System Question for Electronics Whizzes

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He said NMEA heading data has a much higher refresh rate than Seatalk, and that the system would automatically prefer NMEA heading data to Seatalk heading data, and that since I obviously have good heading data in the system, this should solve my problem.
wromg way round, seatalk is faster then nema0183, also the full waypoint names can be transmitted over seatalk, but only 8 chars on nmea ( from memory I beleive).

The other thing is that The Nmea ouput from the corepack is very limited in the data it sends, Ray never intended the corepack to be a seatalk/nmea convertor.

BTW you never mentioned what precisly is the heading data issue.

DAve
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Old 29-05-2011, 10:22   #3
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Re: Nav System Question for Electronics Whizzes

I have a similar set up.
The Raymarine handbook states that the heading data should be sent via NMEA not seatalk, particularly if MARPA is fitted. Speed data transfer is given as the reason.
I assumed since NMEA and seatalk are similar the 2 way seatalk is slower than NMEA, but I have never seen anything other than the handbook to back this up.
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Old 29-05-2011, 10:49   #4
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Re: Nav System Question for Electronics Whizzes

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Originally Posted by goboatingnow View Post
wromg way round, seatalk is faster then nema0183, also the full waypoint names can be transmitted over seatalk, but only 8 chars on nmea ( from memory I beleive).

The other thing is that The Nmea ouput from the corepack is very limited in the data it sends, Ray never intended the corepack to be a seatalk/nmea convertor.

BTW you never mentioned what precisly is the heading data issue.

DAve
Hi Dave: The issue is that the heading data which gets into the chart plotters is corrupted somehow -- sometimes shows the boat headed the right way, but often 30, 60, 90 or even 180 degrees off. It makes MARPA unusable, also radar overlay on the chart. Most irritatingly, the plotter doesn't hold the boat position in the center of the chart -- it will pull back to show more in the direction it thinks the boat is headed. So I end up with a screwed up chart view, to add insult to injury.

I don't need anything out of the corepack but heading. The network gets everything else through different channels. In other words, the only sensor which is connected to the network through the corepack is the fluxgate.
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Old 29-05-2011, 10:50   #5
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Re: Nav System Question for Electronics Whizzes

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Originally Posted by noelex 77 View Post
I have a similar set up.
The Raymarine handbook states that the heading data should be sent via NMEA not seatalk, particularly if MARPA is fitted. Speed data transfer is given as the reason.
I assumed since NMEA and seatalk are similar the 2 way seatalk is slower than NMEA, but I have never seen anything other than the handbook to back this up.
That is entirely consistent with what the guy in Cowes told me!!! I think I'll go for it.
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Old 29-05-2011, 10:53   #6
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Re: Nav System Question for Electronics Whizzes

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That is entirely consistent with what the guy in Cowes told me!!! I think I'll go for it.
Its very easy to do. The RL70 has 2 nmea inputs.
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Old 29-05-2011, 10:57   #7
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Re: Nav System Question for Electronics Whizzes

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Its very easy to do. The RL70 has 2 nmea inputs.
Yes, I already found them! They are bundled with the power cord, and one pair is free!
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Old 29-05-2011, 11:11   #8
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Re: Nav System Question for Electronics Whizzes

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The Raymarine handbook states that the heading data should be sent via NMEA not seatalk, particularly if MARPA is fitted.
Yes but thats the reccomended as the INPUT to the autopilot. This advice is becuase the NMEA input is "dedicated" to the heading data, whereas seatalk is always shared.

But thyats not your problem, yours is the relaying of the heading data to the display. I wonder it is software compatibility issues.

As you said , the heading display on the pilot is "good".

As you say seperately putting the heading data into the RL units ,via NMEA might be useful. BUT you will need to disable the seatalk connection as in general Ray kit prioritises info from the sea talk connection

But what I'd do is feed the heading data into the autopilot via NMEA, not seatalk and then leave the seatalk connection between the RL and the Autopilot.

Dave
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Old 29-05-2011, 11:20   #9
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Re: Nav System Question for Electronics Whizzes

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Yes but thats the reccomended as the INPUT to the autopilot.
No its the input to the RL70. The handbook cautions this should be via NMEA not Seatalk
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Old 29-05-2011, 11:35   #10
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Re: Nav System Question for Electronics Whizzes

yes, but if the fast heading sensor is also connected to the autopilot, I beleive you will have to disconnect the seatalk connection between them. But try it and see.

Most of the RL stuff was written well before autopilot gyros.

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Old 29-05-2011, 11:44   #11
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Re: Nav System Question for Electronics Whizzes

oops, I see I read the original wrong, Absolutly the heading sensor for MARPA use can "ONLY" be input via NMEA. Secondly the heading data that the autopilot needs should then be fed using seatalk from the RL70 to the Autopilot. There shouldnt be a seperate HDG into the autopilot , if there is you may have a problem, as teh RL prioritises seatalk, over HDG.

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Old 29-05-2011, 11:46   #12
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Re: Nav System Question for Electronics Whizzes

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Originally Posted by goboatingnow View Post
yes, but if the fast heading sensor is also connected to the autopilot, I beleive you will have to disconnect the seatalk connection between them. But try it and see.

Most of the RL stuff was written well before autopilot gyros.

Dave
I have a gyro corepack and the heading data is sent to the RL70 via NMEA. Seatalk is also conected. There are sofware setting to prevent any data conflict. So it works fine without disconecting seatalk.
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