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Old 20-03-2011, 09:58   #1
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Heading Sensor for MARPA

Hey Folks -

Does the remote compass (is that what's called a fluxgate compass?) for my wheel pilot (Raymarine X-series) have the ability to serve as a heading sensor for MARPA / Radar overlay???

This MARPA looks like great stuff, but a $700 heading sensor just ain't in the budget. If not the remote compass -- is there any other way to obtain MARPA functionality on the cheap(er)?

TIA
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Old 20-03-2011, 10:05   #2
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Re: Heading Sensor for MARPA

My Raymarine E 80 set up does it automatically. However, I am not impressed with the way the MARPA works on my system. It takes a lot of time to get what appears to be a reliable track.
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Old 20-03-2011, 11:33   #3
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Re: Heading Sensor for MARPA

I have a Garmin 4208, so maybe it is different, but I beleive I need some sort of external "heading sensor". Do you know if the E80 is just using GPS or whether it is using your autopilot's compass? How does the chart overlay work -- is it adequate?
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Old 20-03-2011, 11:45   #4
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Re: Heading Sensor for MARPA

Overlay is good. I think it is using GPS.
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Old 20-03-2011, 12:01   #5
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Re: Heading Sensor for MARPA

If the E80 has a separate 2 wire Heading Sensor output as my Comnav does you simply take it to an unused receive input on the Garmin. No settings it sees it and just works.
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Old 20-03-2011, 12:03   #6
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Re: Heading Sensor for MARPA

Mambo, The raymarine heading sensor , ie the fluxgate for the autopilot, will suffice for Marpa, it will not give a great stabilised picture, but its better then nothing.

Dave
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Old 20-03-2011, 12:10   #7
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Re: Heading Sensor for MARPA

Thanks Dave.

That's the threshold question I had (whether the fluxgate was a heading sensor of sorts) -- and the answer I was hoping for! I'll hook it up and go from there. I am most interested in using the MARPA parimeter alarm anyway so the precise target heading shouldn't be that crucial to that function. Thanks again.
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Old 20-03-2011, 14:42   #8
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You'll find the marpa lock is a problem as is the constant vector recalculations. I always end up turning it off in any conditions where I really need it.

I always wondered if I could feed cog into a mux and change it to heading and use it for marpa. While the accuracy might be a bit suspect for a small boat the damping associated with Cog calculations actually might help MARPA hmmmmm
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Old 22-03-2011, 21:32   #9
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I have much the same question. Do I need both the smart heading sensor and the fluxgate compass or just the compass?
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Old 23-03-2011, 04:00   #10
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Re: Heading Sensor for MARPA

Important issue is that its a fast heading sensor providing updates several times a second. My B & G heading sensor connected via NMEA @ 4800 baud (updates about twice in three seconds) to my Raymarine C80 worked, but gave very shaky data updates when using MARPA.

I would recommend therefore using Raymarine's own fast heading sensor. You only need one source so that should suffice for all other heading needs.
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Old 23-03-2011, 05:37   #11
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Re: Heading Sensor for MARPA

MARPA on the Raymarine E Series setup requires a heading sensor. The fluxgate is that sensor. If you are using the X series autopilot, the heading is stabilized by a laser gyro (inside the autopilot, not the fluxgate). I believe this also to be the case on the S3G systems. The more stable the heading source, the more accurate it can be. The narrower the radar beam, ditto.

However, the results you will get from MARPA require that you understand some of its limitations. When we used to plot targets on the radar screen with grease pencils, we used to put a cross over the target every three minutes. After six minutes we would draw a line joining the crosses and figure out if we were far enough at CPA. MARPA on this system tries to give you the answer much quicker. It takes into account every time the radar beam hits the target and the rate of change. This time is just simply too short, at least in the beginning, so you have to wait quite a bit to get a fairly decent vector. Feeding it anything else, like course, would be using incorrect information. I'm not sure you could anyway.

I hope I'm not preaching to the converted here....sorry if I do.
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Old 23-03-2011, 10:41   #12
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Re: Heading Sensor for MARPA

I also have a 4208 and use my fluxgate compass as a heading indicator for MARPA. We've been very happy with it, especially leaving San Francisco Bay when the first time we saw the Golden Gate Bridge was when we were directly underneath it.

MARPA is not super accurate right now because we need to re-calibrate our compass. I'm not sure if that has to do with all the changes in magnetic variation it's seen since we brought it back from Mexico. Makes for an inaccurate CPA.

I will say that if there's just one target we're concerned about we usually just drop a bearing/range marker and watch that. Then I don't have to wonder if the software is working correctly.
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Old 23-03-2011, 15:35   #13
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Ok,now I'm confused, can anyone tell what hardware I need to add MARPA to my e80 and Raymarine radar?
Thanks
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Old 23-03-2011, 19:08   #14
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Re: Heading Sensor for MARPA

Quote:
Originally Posted by bazzer View Post
Ok,now I'm confused, can anyone tell what hardware I need to add MARPA to my e80 and Raymarine radar?
Thanks
You need a fluxgate, but this is normally connected to the autopilot, which in turn provides gyro stabilization.

Cheers!
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Old 23-03-2011, 19:13   #15
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I don't have a Raymarine autopilot, have a very old, but working alpha system. I do have a fluxgate that i purchased used. But I obviously need some other hardware to connect it to my E80 system to make Marpa work
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