Autopilot always deviates to starboard side of the route [SOLVED - heading offset]

[crck0848]

Can anybody suggest why my autopilot consistently tracks 10-15 yards to the starboard side of my route? In all other aspects, the system performs great, but it always runs to the right of where it should be.

[EDIT: PROBLEM SOLVED. This issue was happening because the SCX20 satellite compass was not correctly aligned with the ship centerline. In other words, the SCX20 was mounted with a heading offset of 2.5 degrees and I did not compensate for it. I fixed the problem by adding a heading offset in the SCX20 setup page. Now the autopilot tracks straight and true. Skip to the end of this thread for details on how I calibrated heading.]


(I also replied to an older thread here: https://furunousaforum.com/threads/20382)

TZT16F chartplotters
SCX20 satellite compass
NavPilot 711C autopilot

My heading doesn't matter ... I'm always offset to the starboard side of the route. If I manually steer back to the route and reengage the AP, it always deviates back to starboard.

See attached screenshot: As I approach the waypoint, I'm offset to the right. The AP steers left to get back onto the route, goes directly over the waypoint, then steers right until it's 10-15 yards off the route again. It's particularly annoying when I'm in a narrow channel or canal. The frequent direction changes confuse nearby vessels.

Grateful for any suggestions.

 

[21Outrage]

I don’t know the answer to your question but venture it may be a deliberate setting, intended to keep you slightly outside of everyone else’s path. If that’s the case I’d wager you can adjust the setting.

 

[crck0848]

Interesting suggestion. But if that were the case, the AP would also leave the waypoints to port, rather than veering left to cross directly over the waypoint. I've dug pretty deep on this one, and can't find a setting anywhere.

 

[gtstang462002]

I have similar issues with mine always tracking to the port side if I am running any mode other than prescise.

 

[JJ Neutron]

Can anybody suggest why my autopilot consistently tracks 10-15 yards to the starboard side of my route? In all other aspects, the system performs great, but it always runs to the right of where it should be. (I also replied to an older thread here: https://furunousaforum.com/threads/20382)

TZT16F chartplotters
SCX20 satellite compass
NavPilot 711C autopilot

My heading doesn't matter ... I'm always offset to the starboard side of the route. If I manually steer back to the route and reengage the AP, it always deviates back to starboard.

See attached screenshot: As I approach the waypoint, I'm offset to the right. The AP steers left to get back onto the route, goes directly over the waypoint, then steers right until it's 10-15 yards off the route again. It's particularly annoying when I'm in a narrow channel or canal. The frequent direction changes confuse nearby vessels.

Grateful for any suggestions.

This could be due to a number of variables: Here are a few things to check... Possibly a faring block for a transducer or some other feature under the hull creating drag, or perhaps the RRU is having an issue, or perhaps something in the steering system linkage etc. or running one engine in a dual engine system while underway.

 

[crck0848]

The rudder signal behaves normally and says 0 when running straight ahead, so I doubt it's an RRU issue. Can't be a problem with the hull or running gear, as the boat runs straight and true under manual control. I've never run the boat on a single engine. The AP seems to know exactly where I am and how to control the boat, but it chooses to deviate to starboard. Keep the suggestions coming!

 

[21Outrage]

The rudder signal behaves normally and says 0 when running straight ahead, so I doubt it's an RRU issue. Can't be a problem with the hull or running gear, as the boat runs straight and true under manual control. I've never run the boat on a single engine. The AP seems to know exactly where I am and how to control the boat, but it chooses to deviate to starboard. Keep the suggestions coming!

Sorry, that must be very frustrating. Hoping for a relatively simple resolution

 

[JJ Neutron]

The rudder signal behaves normally and says 0 when running straight ahead, so I doubt it's an RRU issue. Can't be a problem with the hull or running gear, as the boat runs straight and true under manual control. I've never run the boat on a single engine. The AP seems to know exactly where I am and how to control the boat, but it chooses to deviate to starboard. Keep the suggestions coming!

Would it be possible for you to post some photos of the SCX20 as it is installed on the boat with any surrounding equipment in the photo, also an under hull photo if you have one from when the boat was out of the water last. Perhaps some photos of the steering system linkages and hydraulic lines too? Maybe having a look at these items may reveal something to help diagnose the root cause.

 

[crck0848]

The SCX20 has a great view of the sky -- highest point on the boat, well above the beam of the radar. Re: running gear and hydraulics, keep in mind that everything acts perfectly normal under manual control. I don't want to assume anything ... just don't understand the question.

 

[Kevin J]

Hi. I am going out of the box. Not knowing how long you have had the boat or what work has maybe been completed.
Are both rudders the same?
And check for metal objects around heading sensor. Maybe complete a new calibration.

 

[crck0848]

Hi Kevin - the rudders and all rudders are in perfect shape, and the boat drives normally when I'm driving by hand. I have a satellite compass, so it's not relying on a magnetic compass.

 

[Johnny Electron]

Wow while it is hard to tell in photos; that looks right in the radar beam. It also is balanced on that support which is likely to vibrate and be a real issue. If inside the radar beam the front end amp is going to eventually get damaged. I don't know if that is what is affecting the pilot but that SCX20 location and mounting doesn't look good to me.

 

[crck0848]

Hey Johnny. Don't be mislead by the photo. After discussions with you and others, I made sure to mount the SCX20 out of the radar's beam.

But, as I've said, the SCX20 works just fine and has been 100% reliable. This is not an issue related to the compass, running gear, or steering. The AP apparently receives solid information about exactly where I am, and it can control the boat's position with great precision. The problem is that the AP is choosing to run outside of my chosen route.

Just to reiterate: The AP consistently runs to the right of the route, then turns left to pass directly over the waypoint, then deviates back to the right. Seems like an algorithm problem, not a sensing problem.

 

[Quitsa]

It sounds as though you are describing an issue that occurs when you are in NAV mode steering to a waypoint or following a route. What happens when you are in auto mode (set to "advanced auto")? If you haven't already done so, after you set a waypoint or route on the plotter, try putting the autopilot in "AUTO" setting the compass heading to the bearing to the waypoint shown on the plotter and see if the boat stays on the course line.

Also a slightly off the wall question -- is it possible that your TZT display is set to show heading data in true and the autopilot in magnetic (or vice versa)? That would probably make the boat weave around the course line rather than run parallel but who knows.

 

[crck0848]

@Quitsa -- Thanks for the suggestions. The AP and chartplotters are set up to use the SCX20 satellite compass as the data source for position and heading. I've used true heading instead of magnetic for every setting I can find, but maybe I missed a setting somewhere.

If I use "go to waypoint," the AP behaves the same as when following a route: it deviates right then comes back left to pass over the waypoint.

In Nav mode, as far as I can tell, it travels a straight line.

 

[Quitsa]

My suggestion was a bit different that using "go to waypoint." First choose a waypoint on the chartplotter and set it. But don't use NAV mode on the autopilot or accept the prompt on the chartplotter to use the autopilot. Instead, set the autopilot in "Advanced Auto" mode on the compass heading that will take you straight to the waypoint.

Do you have the 711C set to "sensor synch"? Try using that if you don't.

This is a very odd issue. I have a 711C and it steers to a waypoint in NAV with a course deviation of less than 3-5 yards. It may drift to one side or the other but only for very short periods of time. It will also track straight in AUTO mode if I set the heading to the bearing to waypoint as I suggested you try.

Seeing S curves around the course line is not uncommon and can have a number of known causes. But running parallel to the course line as you describe is just plain weird. I don't see how it could be a software issue because then it would happen to other people.

 

[crck0848]

While poking around trying to follow these suggestions, I stumbled across the problem: the SCX20 satellite compass is not perfectly aligned with the ship centerline. It apparently has a heading offset of 2.5 degrees that I failed to compensate in the settings. I've now corrected it, and the 711C drives a course that stays dead on top of the route. Happy!

Here's how I calibrated the heading offset:

Drive boat at 8 knots in a straight line with no cross-current and zero rudder angle.
Red dashed line indicates course over ground.
On 711C, press "Auto".
Blue line indicates autopilot heading.
Blue line should lay directly on top of red dashed line.
If not, go to the SCX20 page and adjust the SCX20 HDG offset.
Repeat until they line up perfectly.

Thanks for all the suggestions. I'll update the title and initial entry for future readers.

 

[crck0848]

Product request: make it easier to calibrate SCX20 heading offset. Ideally, once I'm underway with no cross-track speed, I could just poke a button that says "update the heading offset so that HDG matches COG."

It would work best for high-speed boats. For slow boats, it would rely on having no cross-current or cross-wind.

 

[Syed Owais]

[EDIT: PROBLEM SOLVED. This issue was happening because the SCX20 satellite compass was not correctly aligned with the ship centerline. In other words, the SCX20 was mounted with a heading offset of 2.5 degrees and I did not compensate for it. I fixed the problem by adding a heading offset in the SCX20 setup page. Now the autopilot tracks straight and true. Skip to the end of this thread for details on how I calibrated heading.]

Thanks for the information.

 

[jp498]

Last few installs, I have fastened down the SCX20 with just one screw until I'm happy with the alignment. Then after that I drill/silicone/fasten the other three. I'm typically installing SCX20 for radar, and I run straight toward a lone radar target (such as a channel buoy) to fine tune the radar alignment on the normal (ppi) radar display. Then I can adjust the sat compass so that overlay and AIS targets lines up good.