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Heading Sensor with Garmin Chartplotter and Radar

Old 09-29-2020, 02:14 PM
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Default Heading Sensor with Garmin Chartplotter and Radar

I ordered a boat with Garmin 942xs chartplotter and Fantom 18 radar. Salesman never mentioned needing a heading sensor.

I found a page on Garmin's website where they recommend adding a Heading Sensor when using a Garmin Chartplotter: Heading Sensor Recommendation. My question: Has anyone tried using a Garmin Chartplotter without adding a Heading Sensor and found the displayed heading accuracy acceptable? It seems to me that if a heading sensor was that critical a requirement it would be included with the chartplotter. Garmin's recommendation makes it sound like once you are moving, the chartplotter uses COG, which I hope is relatively accurate. Just trying to determine how important having a heading sensor is for the chartplotter to display accurate information when I'm moving.

Regarding the radar, I realize that you don't have MARPA without a heading sensor. I'm not all that sure what exactly MARPA is, and how important that feature is. I'm more concerned about having accurate direction/heading information displayed on the chartplotter when I'm moving.
Old 09-29-2020, 04:05 PM
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As long as you are moving it will be fine. Once you are stopped the satellites don’t know which way you are facing so your plotter will be off. The radar will still show targets wherever they are accurately
Old 09-29-2020, 04:09 PM
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I have a 942 and bought a Garmin Steady Cast heading sensor. There is another thread on here with many people having poor performance from them but mine has been working great all summer. It is a low cost model compared to others so I took a chance. Most issues seem to be from bad mounting locations to me. COG is very accurate and as long as you are moving is all you need. Without a heading sensor your chart or boat heading depending on your chart orientation spins around while not moving making it hard to know where the wrecks or reefs are in relationship to your position. Money well spent in my opinion.
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Old 09-29-2020, 05:27 PM
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Originally Posted by h_bar View Post
I ordered a boat with Garmin 942xs chartplotter and Fantom 18 radar. Salesman never mentioned needing a heading sensor.

I found a page on Garmin's website where they recommend adding a Heading Sensor when using a Garmin Chartplotter: Heading Sensor Recommendation. My question: Has anyone tried using a Garmin Chartplotter without adding a Heading Sensor and found the displayed heading accuracy acceptable? It seems to me that if a heading sensor was that critical a requirement it would be included with the chartplotter. Garmin's recommendation makes it sound like once you are moving, the chartplotter uses COG, which I hope is relatively accurate. Just trying to determine how important having a heading sensor is for the chartplotter to display accurate information when I'm moving.

Regarding the radar, I realize that you don't have MARPA without a heading sensor. I'm not all that sure what exactly MARPA is, and how important that feature is. I'm more concerned about having accurate direction/heading information displayed on the chartplotter when I'm moving.

MARPA:

Mini-automatic radar plotting aid (or MARPA) is a maritime radar feature for target tracking and collision avoidance. Targets must be manually selected, but are then tracked automatically, including range, bearing, target speed, target direction (course), CPA (closest point of approach), and TCPA (time of closest point of approach), safe or dangerous indication, and proximity alarm.
MARPA is a more basic form of ARPA (automatic radar plotting aid).



Heading sensor...

The Garmin Steady Cast is inexpensive...and improves bow orientation on the plotter to help match ones heading
Old 09-29-2020, 05:43 PM
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You should check with Garmin if the Fantom Doppler processing is working without a heading sensor.
Old 09-29-2020, 05:54 PM
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Originally Posted by Dirt Sailor View Post
I have a 942 and bought a Garmin Steady Cast heading sensor. There is another thread on here with many people having poor performance from them but mine has been working great all summer. It is a low cost model compared to others so I took a chance. Most issues seem to be from bad mounting locations to me. COG is very accurate and as long as you are moving is all you need. Without a heading sensor your chart or boat heading depending on your chart orientation spins around while not moving making it hard to know where the wrecks or reefs are in relationship to your position. Money well spent in my opinion.
Yes it is inexpensive. I did see that thread about problems with the Steady Cast, and was concerned I'd be wasting my money. I guess I'll give it a try.
Old 09-29-2020, 05:54 PM
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5 minutes after adding my MFD, I went online and ordered a SteadyCast heading sensor. So yes, I guess you could say I tried running without one. I wouldn't recommend it. When you are stopped, you'll see the chart (and Radar) oriented in some random direction having nothing to do with where your bow is pointed. I'm actually surprised they even sell Radars without heading sensors. The SteadyCast has worked flawlessly for me, btw.
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Old 09-29-2020, 06:25 PM
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If you dont use a heading sensor, Garmin uses COG. Wind current etc can affect your direction regardless of where you are heading, if you are moving perfectly without influence from wind, current, waves, etc. then there would be no need. However that is not the case when boating.

Below is an example of the difference between heading and COG. The green line is my heading line and the dotted red line is my coarse over ground. You can see that they do not line up and the difference is the further you go out. This is how far off my overlay would be if it were to use COG instead of heading.


Old 09-29-2020, 06:30 PM
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Originally Posted by iFishMD View Post
...Below is an example of the difference between heading and COG. The green line is my heading line and the dotted red line is my coarse over ground. You can see that they do not line up and the difference is the further you go out. This is how far off my overlay would be if it were to use COG instead of heading.
It appears you are virtually sitting still (0.1 kn). I agree when still or drifting COG will be wrong.
Old 09-29-2020, 06:42 PM
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Originally Posted by h_bar View Post
It appears you are virtually sitting still (0.1 kn). I agree when still or drifting COG will be wrong.
while the photo above is at 1.2kn. Current and wind has an influence even at speed and will make the overlay inaccurate. Unless you are running with no wind or current influence then a heading sensor is highly beneficial for radar overlay


Old 09-29-2020, 06:48 PM
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When I see all the questions at THT about heading sensors I'm wondering why people don't have autopilots which can provide heading. An autopilot would be higher on the priority list than a radar for me, but maybe they don't have any experience with autopilots. If they had I'm sure they would have installed an autopilot.
Old 09-29-2020, 06:51 PM
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Originally Posted by iFishMD View Post
...Current and wind has an influence even at speed and will make the overlay inaccurate. Unless you are running with no wind or current influence then a heading sensor is highly beneficial for radar overlay
I'm sold. Not that expensive. Having said that, it was my understanding COG without a heading sensor comes from GPS. How does wind and current affect GPS? Satellites know where you've been irrespective of wind and current, and plotter uses those points to determine direction. But i may be wrong.
Old 09-29-2020, 06:53 PM
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Originally Posted by abbor View Post
When I see all the questions at THT about heading sensors I'm wondering why people don't have autopilots which can provide heading. An autopilot would be higher on the priority list than a radar for me, but maybe they don't have any experience with autopilots. If they had I'm sure they would have installed an autopilot.
Autopilots usually come with heading sensors

Autopilot = convenience
Radar = Safety tool
Old 09-29-2020, 06:55 PM
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Originally Posted by iFishMD View Post
Autopilots usually come with heading sensors

Autopilot = convenience
Radar = Safety tool
Autopilot = thousands of $$
Heading Sensor = $150
Old 09-29-2020, 06:57 PM
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I wouldn't need a safety tool if I would hardly leave the sorroundings of the harbour, and that would have been the situation for me without an autopilot.
Old 09-29-2020, 06:57 PM
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Originally Posted by h_bar View Post
I'm sold. Not that expensive. Having said that, it was my understanding COG without a heading sensor comes from GPS. How does wind and current affect GPS? Satellites know where you've been irrespective of wind and current, and plotter uses those points to determine direction. But i may be wrong.
When you are running in seas with wind and current. the boat is not necessarily heading (pointing) in the direction it is going. (doglegging) Therefore you are facing (heading) a few degrees off from the direction you are running (coarse) . The further out you go the less accurate your overlay will be. It is why ALL other brands except Garmin require a heading sensor for overlay and other higher end functions and do not just use COG.
Old 09-29-2020, 07:00 PM
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Originally Posted by iFishMD View Post
When you are running in seas with wind and current. the boat is not necessarily heading (pointing) in the direction it is going. (doglegging) Therefore you are facing (heading) a few degrees off from where you are running. The further out you go the less accurate your overlay will be. It is why ALL other brands except Garmin require a heading sensor for overlay and other higher end functions and do not just use COG.
Agreed. COG (GPS) calculates actual direction of travel, irregardless of how boat is pointing.
Old 09-29-2020, 07:07 PM
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Originally Posted by h_bar View Post
Agreed. COG (GPS) calculates actual direction of travel, irregardless of how boat is pointing.
Now given that radar is fixed to where the boat is pointing (heading). When you lay it over a chart that is showing COG, the overlay will be off based on the difference in that cog and heading making the overlay inaccurate.
Old 09-29-2020, 07:21 PM
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Originally Posted by iFishMD View Post
Now given that radar is fixed to where the boat is pointing (heading). When you lay it over a chart that is showing COG, the overlay will be off based on the difference in that cog and heading making the overlay inaccurate.
OK. We agree. When COG and heading of boat is different then radar overlay will be inaccurate on chartplotter display. Heading Sensor fixes this.
Old 09-29-2020, 09:34 PM
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Without a heading sensor you can run a separate screen (split) of the Radar. Just run it in head up mode. The lubber line always stay up or never moves. All targets would be relative to the bow. That’s the only way a lot of people run. I prefer N up which does require a sensor.
I don’t have Garmin but all the plotters I’ve ever run if you leave the charting in N up mode it won’t move the charting all over the place. Your boat icon could be pointing wrong when drifting as the gps will compute the drift direction as course. Anyway it works.
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