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Garmin GHC 20 and shadow drive

Old 11-23-2017, 03:48 AM
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Default Garmin GHC 20 and shadow drive

Ok... i just had a garmin ghc 20 autopilot installed in my 2017 Everglades 295cc with Seastar Optimus steer-by-wire and twin Yam 300’s. I was playing around with the autopilot for the first time yesterday and already have some questions.

1. Does the system ‘learn’ the boat as it goes? At first when engaging the AP it seemed to make a crazy turn and then correct.

2. When taking over the helm to turn around an obstacle (buoy) while AP is engaged on a route, the Shadowdrive allows you to do this apparently. However, after letting go of the wheel after avoiding said obstacle, does the AP automatically take back over and get you back on the course/route you were following? My AP appeared to go into ‘heading hold’ after making a course adjustment and not resume the route that was being followed prior to course adjustment. How do I get it to resume the route after the brief course adjustment?

3. My AP compass is a few degrees off from my garmin 7616 compass reading. And my 7616 compass reading is almost 10deg off from my Ritchie compass mounted on top of my helm station. Recommendations?

Thanks!
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Old 11-23-2017, 04:37 AM
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1. can't speak to that

2. my perception is that, once in Shadow Drive, there is some small tolerance of time whereby manually returning to the intended course will automatically re-engage the AP to "Follow route" - the "magenta line"

sometimes - not always - I will get a prompt on the MFD - something like "do you want to return to Follow Route"

but sometimes, swing too far off, or stay in Shadow long enough, seems there is no prompt, the AP simply goes into "Heading Hold"

in which case, the only way I know to get it back into "follow route" mode is with the Menu button on the GHC - manually select "Engage route"

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3. "Calibrating the compass" - the heading sensor of the AP - is part of the setup procedure and can be repeated if necessary.
The Ritchie is of course showing Magnetic North
the GHC and your MFD can display in either Magnetic (M) or True (T) - which do you have set?
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Old 11-23-2017, 04:47 AM
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Default Compass

I know my everglades dealer, who did the AP install, set the AP to true north. I’m not sure about my MFD’s. I bet they (twin 7616’s) are true north as well. Recommendations?
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Old 11-23-2017, 06:46 AM
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Its completely your preference to how its configured -

personally, I have Magnetic on everything, so they "match" -
Although checking just now, I see there is ~5 degree difference between the AP's heading sensor and my "real" compass
frankly, I have no idea which is "right" -
its close enough that I don't notice when using them
and I'm completely satisfied with the performance

Keep in mind:
- your Ritchie may be "off"
- the MFD does not have a "compass" - for showing the boat's heading,
you select whether it uses the AP's heading sensor, or calculates "GPS heading" -
the latter is derived from your boat's change in position, so is only accurate when the boat is moving, AND pointed in the same direction that it is moving
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Old 11-23-2017, 07:08 AM
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Default Magnetic

I just checked... i have everything set to magnetic north. The AP and MFD are showing the same heading... but both are off by 14 degrees from my Ritchie Compass. Any way to calibrate the Garmin’s To the Ritchie so they are the same?
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Old 11-23-2017, 10:53 AM
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1 no. You must calibrate it during seatrail. It will do an auto learn and zigzag back and forth.

2. No. It will set on new heading.

The "heading" reading. Will be the same on both. You are probably looking at heading in gch20 and cog on the plotter. Which are different things.

If your heading and cog are within 3 degrees. Then it's probably the mag compass that is wrong.
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