AutoPilot, Safe course line, Boat angle & Radar

[baz]

I use my Auto Pilot quite frequently and have noticed I have to be careful interpreting the Radar overlay when looking for other boats/objects displayed on the Navigation chart by orange blips with respect to my plotted safe course track line.

Quite often my boat shape displayed on the chart is at an angle to the safe course track line -- see picture below (for some unknown reason it can take a few moments to display). In this example I was fighting a strong headwind which was blowing on my port bow somewhat... not sure what the tide/current was doing. I'm assuming it's not unusual for the boat to 'crab' along the safe course track much like an aircraft would do when landing with a strong cross wind.

With Radar overlaid on the chart the various boats/objects nearby are displayed as orange blips of various sizes -- small and large depending on the boat/object size.

I've noticed that when looking for the boat or object that the Radar has picked up with respect to the safe course track line does not correspond to my boat's heading. When this happens my boat shape displayed on the chart is at an angle to the safe course track line. If I use the boat shape's angle and look for where the orange blips are I find and can see what the Radar is picking up.

My question to others here is -- is the boat's angle on the chart an accurate representation of my boat's heading with respect to the safe course track line. According to the Radar it certainly appears to be so. I say this as when the boat's shape is perfectly aligned with the safe course track line the Radar's orange blips accurately show where the other boats/objects are.

If I'm not making myself clear, please post back for further explanation of this issue. I want to satisfy myself I'm correctly interpreting the Radar displayed objects with respect to my boat's heading as we do get fog conditions in my area.

 

[Levitation]

My take on this - based on my airplane radar use - no significant time with boat radar usage...
The radar does not know what your CMG is...
The angle to a radar return is relative to the boat's electric compass heading, not the ground track...

An extreme case would be a 6 knot sailboat's radar shows a small island straight ahead 10 miles... But an extreme tide is pushing the boat directly sideways at ten knots... The boat will never reach the island... You need to use a paper plotter to track radar returns for possible intersections...

 

[Shared Dream II]

From the picture provided, it would appear that your system is out of calibration. Note that the radar painting of the shoreline is off by the same amount that your boat heading deviates from the aoutopilot course line. Check to see if the GPS heading on the charplotter is the same as the heading that is displayed by the autopilot on the GHP 10 display. If they have a different reading that is relatively constant, you may need to recalibrate the autopilot.

 

[baz]

From the picture provided, it would appear that your system is out of calibration. Note that the radar painting of the shoreline is off by the same amount that your boat heading deviates from the aoutopilot course line. Check to see if the GPS heading on the charplotter is the same as the heading that is displayed by the autopilot on the GHP 10 display. If they have a different reading that is relatively constant, you may need to recalibrate the autopilot.

That's good advice... will do. Thanks. 🙂

Is this re-calibration something a layman can do (i.e., me) or will it be necessary to secure a skilled Garmin technician for the task ? Maybe I'll call Andrew to get his inputs on this aspect.

 

[baz]

The Garmin 5212 chart plotter's GPS heading and the AutoPilot's heading are in agreement...

 

[Stella Maris]

Barry,
I may be wrong but, I think your instruments are off by 60 degrees...... 342 degrees is not the same as 042 degrees.....

 

[GulfSailor]

I may be wrong and just adding to the confusion, but it appears to me the the plotter is displaying the boat's heading generated from the compass input, and the track or COG generated by the GPS input.

In other words the boat is following the correct path, but as you're fighting either current or wind or both, the boat is crabbing and the bow isn't facing the direction of travel.

 

[baz]

Barry,
I may be wrong but, I think your instruments are off by 60 degrees...... 342 degrees is not the same as 042 degrees.....

Yea -- I was/am a little confused with the 342 vs. 042. So I will be checking this out some more. The photo was taken with boat docked and under cover by large metal roof which may be obstructing satellite for GPS.

 

[baz]

GulfSailor:

This is my interpretation also. On my return journey along the same course the boat icon was perfectly aligned with the safe course track as there was little wind which was in same direction as my course and tide was in my favor.

 

[Shared Dream II]

Barry
The calibration is something you can do. You will need to get to the sea trial wizard, which is what the factory does when they sea trial your boat. Andrew can help with how to get to the wizard. You will also need a relatively calm wind and sea day.

 

[baz]

Thanks Shared Dream II. Will do with a calm wind & seas. Thanks... 🙂

 

[baz]

I found this snippet (compass info highlighted in red)... GHP10MarineAutopilotSystem_InstallationInstructions.pdf

Completing the Sea trial Wizard:

Drive to calm, open water and, if the Sea Trial Wizard does not start automatically, select Menu > Setup > Dealer Autopilot Configuration > Wizards > Sea trial Wizard. The Sea Trial Wizard welcome screen appears on the GHC 10. Select Begin to start the wizard.

Configuring the planing RPM:

1. Follow the directions on the GHC 10.

2. Note the RPM reading from the tachometer on the dashboard of your boat at the point your boat transitions from displacement to planing speed.

3. If the tachometer value does not match the value on the GHC 10, use the arrows to adjust the value.

4. When you are finished, select Done.
NOTE: If you have a displacement-hull boat, there will not be a transition point for you to set. Instead, adjust the Planing RPM to the highest possible value (6,000 RPM).


Calibrating the compass:

1. Before you begin the compass calibration procedure, drive your boat in a slow, straight line and wait for the wake generated by the planing RPM configuration procedure to pass.

2. Select Begin.

3. When instructed, turn the boat slowly clockwise, taking care to make as steady and flat a turn as possible. Turn slowly so that the boat DOES NOT list.
NOTE: If you have a dual-engine boat, slowly run the port engine forward and the starboard engine in reverse to pivot on a stationary position.

4. After you successfully complete the calibration, and the GHC 10 displays a completion message, select Done. If the calibration fails, select Retry to begin the process again.

 

[baz]

Barry,
I may be wrong but, I think your instruments are off by 60 degrees...... 342 degrees is not the same as 042 degrees.....

Yea -- I was/am a little confused with the 342 vs. 042. So I will be checking this out some more. The photo was taken with boat docked and under cover by large metal roof which may be obstructing satellite for GPS.

So checked this out today... Took boat out for a short run and selected the Auto Pilot to hold a heading of 200ºM. The Chart plotter showed 201ºM and sometimes 202ºM.

So the issue was related to having the boat stationary/docked, under cover. At this point I'm assuming Auto Pilot's compass is AOK.

However, there was one thing that seemed strange to me on this run... When I motored south without auto pilot engaged the course GPS headings matched up very well... but when I turned the boat to a northerly direction the Chart plotter's heading was as much as 20ºM off from the Auto Pilot's heading display. I kept the boat moving northerly but the chart plotter continued to be way off. I turned south again and both matched up very quickly. Very weird.

I played with the Auto Pilot's save course and found my boat's icon on the chart plotter was perfectly aligned with the safe course track line. This was so traveling to the south and to the north. There was little to no wind, very calm seas and it was slack tide conditions.

Does anyone have an explanation when I was traveling north without Auto pilot engaged why the chart plotter would display a heading as much as 20ºM off from what the auto pilot's displayed.

 

[baz]

RE: GHP 10's Wizards... I followed the Garmin's instructions using their "GHP 10 Marine Autopilot System Installation Instructions" guide and found a few things missing that one has to do in order to get at the Wizards...

To get the Wizard display to show one must

1. Not have engine running Garmin does not say to do this.
2. Power off the GHP 10
3. Press the right most two buttons (center one and right most one) while also pressing the power button
4. Wait a short while until the Heading screen appears
5. Now select Menu->Setup
6. If the option for Dealer Autopilot Configuration is shown then you did the above correctly

When running the Dockside Wizard configuration and getting to the RPM Source selecting the NMEA 2000 cannot be done UNLESS you have the engine running. This is not mentioned in the Garmin's instructions.

BTW... I changed the Lock to Lock option from 4.0 to 4.1 for my R-25. I know that my wheel turns a tad more than 4 full turns.

 

[walldog]

Barry,
I may be wrong but, I think your instruments are off by 60 degrees...... 342 degrees is not the same as 042 degrees.....

Yea -- I was/am a little confused with the 342 vs. 042. So I will be checking this out some more. The photo was taken with boat docked and under cover by large metal roof which may be obstructing satellite for GPS.

So checked this out today... Took boat out for a short run and selected the Auto Pilot to hold a heading of 200ºM. The Chart plotter showed 201ºM and sometimes 202ºM.

So the issue was related to having the boat stationary/docked, under cover. At this point I'm assuming Auto Pilot's compass is AOK.

However, there was one thing that seemed strange to me on this run... When I motored south without auto pilot engaged the course GPS headings matched up very well... but when I turned the boat to a northerly direction the Chart plotter's heading was as much as 20ºM off from the Auto Pilot's heading display. I kept the boat moving northerly but the chart plotter continued to be way off. I turned south again and both matched up very quickly. Very weird.

I played with the Auto Pilot's save course and found my boat's icon on the chart plotter was perfectly aligned with the safe course track line. This was so traveling to the south and to the north. There was little to no wind, very calm seas and it was slack tide conditions.

Does anyone have an explanation when I was traveling north without Auto pilot engaged why the chart plotter would display a heading as much as 20ºM off from what the auto pilot's displayed.

Barry, check and make sure that you do not have any metal items stored near or against the chartplotter's compass. On our boat it is located in the cave. I built shelves around it and we found that can goods have an interesting effect on the heading of the chart. Now we make sure that only cereal boxes are near this sender.

 

[baz]

Herb: I will look for where the chart plotter's compass is. At this time I don't have a clue where it is.

I do know where the auto pilot's CCU is... It's located in the bow storage hold under the starboard bow berth's cushion.

Maybe other R25 owners can post back where the chart plotter's compass is likely to be located.

 

[baz]

Herb:

The Chart Plotter does not have a compass. It gets its heading info from the Satellite(s) ONLY when you start to move the boat. The Auto Pilot's compass is in and under the bow's berth starboard locker, close to the center line. It has no metal object close to it. Its compass should be accurate with the boat stationary.

Ref: My OP... The aspect of the Chart Plotter showing a different heading to that displayed on the GHP 10 Auto Pilot's heading screen with the boat docked (and not moving) is therefore due to the way the Chart Plotter obtains its heading info -- it's simply inaccurate unless the boat is moving.

As an aside... I talked with Andrew this morning about traveling southerly with Auto Pilot and Chart Plotter having essentially identical heading values vs. traveling northerly and there being as much as 10ºM to 20ºM discrepancy between the Auto Pilot and Chart Plotter's heading numbers. Andrew indicated that this should be expected, and if I recall our conversation correctly, the Auto Pilot is the more accurate heading info. I'm still a little confused why the Chart Plotter should be off mind you as it's getting its info from the Satellites just as it did when traveling in a southerly direction. Maybe others can explain why this discrepancy occurs... thanks.

 

[walldog]

OK the Auto Pilot's Compass causes a weird display on my chartplotter when can goods were stacked around and near it. I was getting vertigo watching it and trying to resolve what I was seeing out of the windshield with the views on the chartplotter. Doing a figure 8 corrected it for a brief time and then it reverted to the off kilter display. Moving the can goods away from it corrected the problem. Just saying.