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Hi Folks,

Just wanted to correct something that I had read, or been told, a couple of times.
I was told that you could not have radar overlay (over chartplotter map/gps) without buying some type of electronic compass, gyro compass, etc (or having one that comes with an autopilot). I was also told, when buying the 18" Raydome, that the GPS required the boat to be travelling at least 3 kts to give heading direction.

Anyway, connected the radar to my Raymarine C80 multifunction plotter and it works great, without the additional compass, etc.
Note: I am certain that it would work even better with one, as the radar targets would be centered more precisely over the islands, etc, if the boats heading was more quickly updated to the plotter. However, for my intended use, it works great as is. If I change headings quickly, the radar overlay is a bit off of the map, fo a couple of seconds, and then it is fine again. I generally sail in an area with lots of islands, and the radar overlay shows a pink radar cloud over each island on the plotter. Of course, other pink marks, where no islands are marked on the map, are possible boats, etc.

I found I did have to adjust the gain or tune, to filter out some false targets, from waves (winds 15 -20kts), but was still able to see the real targets. Of course, I need to read / learn alot more about these functions in order to get the most out of it. Auto mode worked most of the time, but did pick up to many false targets at times.

I can't comment, or compare my new radar to the digital or HD radar options out there, as my 1 year old plotter is sadly not capable of connecting to them (not happy with Raymarine or dealer for not telling me this at time of purchase).
Although the newer versions of radar may be superior, this one certainly seems to do what I need. You can of course, split the screens as well, so you can see the chart on one side, and the radar on the other, but to me the overlay screen is the cat's a$$!

Although we did travel more 4-6 kts most of the time, while sailing, the plotter / radar overlay also worked fine when trolling / fishing at 1-2kts.
 

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You are correct in that the overlay works fine without a heading sensor. The C80 assumes that the direction you are heading is the head up direction. This can make the display a little off, and a little slow to correct for rapid changes. You will find that if you add a sensor or an autopilot to the system, the head up direction will correct quicker.
 

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Furuno Radar/Chartplotter

Interesting that the Raymarine unit allows for overlay without the heading sensor whereas my Furuno unit installed 2 years ago does not.
 

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Senior Mumble
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I have the C80 and enjoy the overlay display. Having the S1 Wheelpilot, I have an electronic compass, but haven't found that resolves all problems. When returning from a fireworks display last Saturday night, I was using the radar overlay function and the chart and radar did not match up. The radar was in heads-up mode (I was going basically North) while the chart was oriented -90 degrees. I had radar sync set to "on". When I went to a side by side display mode, the chart was still off by 90 degrees and showed me backing out of Hempstead Harbor! If I had been unsure of my position (and this did happen at night!), it would have been dangerous. It showed me heading into a breakwater when I was heading away from it. I also noticed my autopilot had my course off by 180 degrees. I turned off both the autopilot and the C80. I turned the C80 on first, then the autopilot. After doing this, everything got back to normal. I have no idea what caused this. Raymarine is so far mute on the issue.
 

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You'll find all those gadgets more useful on heavy seas, with a lot of move, or if you installed your antena too high. GPS updates, although slow and requiring some boat speed, will provide the heading info you need. The Gyro (if your autopilot have one) will provide boat acceleration info, so your image will look steadier. But that's all, I had it in both ways, and found it more accurate/faster just under severe sea conditions.The remaining 90% of time, I think gyro didn't add too much value for the charting (ok, improved the AP a lot !!!), and even MARPA shows target info with same errors I had before. I don't use overlay too much as I think the screen gets too poluted, and prefer the black background for my old eyes ....
 

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Telstar 28
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One reason I think chart overlay is pretty good for newbies is that it gives you a way to tell what you're looking at more easily...Learning to interpret the radar image is a bit difficult at first for a lot of people. Being able to see the radar image and the underlying chart helps show how ATONs, land, etc will be represented and makes interpreting the radar image easier for the new user.
 
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