NavPilot 711C Steering

[Quitsa]

My 711C seems to steer with much less wandering when using "Auto" mode than when in "NAV" mode. It is not consistent, however. Sometimes the NAV mode does very well and will stay within 3-4 yards of the course line without S curves or hunting. Other times it will get off course 20-30 yards and then correct and get off course 20-30 yards on the other side.

I have an SCX-20 providing heading and GPS data.

The only factor that I have identified that has some bearing on it is the use of trim tabs. The trim tabs certainly can "steer" the boat if it is heeling slightly to one side or the other. If I run with the autopilot in standby and the rudder straight and minimize the steering effect from the trim tabs, the NAV mode definitely works better.

I don't understand why the Auto mode would handle the trim tab so much better.

Now I have the steering mode set to "Full Auto". Is there a manual parameter input I could make to help the autopilot do better in NAV mode especially in dealing with the impact of the trim tabs?

 

[FishTech]

Do you have automatic trim tabs, like ZipWake or some other brand? Those constant adjustments to boat handling characteristics will cause autopilots to wander.

 

[gtstang462002]

I have similar issues. The only thing that I have found for accurate plot lines is to use XTE precision over XTE economy or course settings. The only issue I have with precision is when the waypoint changes, it overcorrects just to get back to the "purple" line. If I use AUTO mode for holding a course I generally don't wander too much, but at times I have seen it get as far off as 15 degrees of the set heading. The only thing that seems to correct it is giving the knob a click one way or another by one degree and the boat will correct to that heading. :questions

Edit, I do have zipwake trim tabs on my boat, but had the same issues when I had the old school Bennett trim tabs also. The zipwakes take the roll out of the boat when traversing rough seas, otherwise they run pretty smooth.

 

[Quitsa]

Do you have automatic trim tabs, like ZipWake or some other brand? Those constant adjustments to boat handling characteristics will cause autopilots to wander.

No, I have manual Bennett hydraulic tabs. My boat is cold-molded and quite light and the tabs are pretty big.

I noticed in the manual yesterday one setting with which I have not experimented, which is "Response". I have had it set on auto. I wonder if using a high manual value would help? Has anyone tried this?

 

[FishTech]

A higher level of "Response" will make the boat work harder to get back on course from effects of wind, seas, and current. I would try it and see if you find improvement. You could also switch from Full-Auto to Semi-Auto under "Sea State".
One more thing that I have seen correct oddities is running the dockside rudder test again. Ensure that you are in the water, engines are running and any power assist pumps are operational.

 

[Quitsa]

A higher level of "Response" will make the boat work harder to get back on course from effects of wind, seas, and current. I would try it and see if you find improvement. You could also switch from Full-Auto to Semi-Auto under "Sea State".
One more thing that I have seen correct oddities is running the dockside rudder test again. Ensure that you are in the water, engines are running and any power assist pumps are operational.

I thought I would report back that I changed the response setting from "auto" to a manual setting and also changed the sea state setting to to "semi-auto." This seems to have gone a long way to solving the problem, though I probably need to do more experimenting with the manual response setting. Yesterday I ran about 35 miles steering to a waypoint in NAV mode and the boat was wandering 20-30 yards off the course line before I made the changes. Afterwards, it generally stayed within 10 yards and even less for much of the time. Conditions would have been quite challenging for the autopilot with a 2 foot wind waves on top of a big 4-5 foot swell running from a different direction.

One interesting question is what happens with sea state parameters in full auto mode. I wonder if changes in the boat's handing characteristics from adjusting the trim tabs on a boat like mine where it makes a big difference cause the "self-learning" algorithm to make changes that then become the wrong settings if the trim tabs are adjusted and lead to the poor steering performance I experienced.

 

[Johnny Electron]

Autopilots can't fight trim tab and zip wakes very well. These items will alway cause problems at times whenever it comes to operations of a pilot. The adaptive learning will adapt somewhat but it is very easy for automated trimming systems to complete mess up the control of a pilot.

 

[Quitsa]

Autopilots can't fight trim tab and zip wakes very well. These items will alway cause problems at times whenever it comes to operations of a pilot. The adaptive learning will adapt somewhat but it is very easy for automated trimming systems to complete mess up the control of a pilot.

My trim tabs are manual. However, it is certainly true that the autopilot has trouble when the trim tab setting causes the boat to steer one way or the other or changes the rate of turn introduced by heeling from wave action. I can easily understand how an automated trim system would create a difficult feedback loop and mess up the steering.

The manual response rate setting does help by introducing faster corrections. It's a bit of trouble, but for longer runs steering to a waypoint, I will put the pilot in standby, center the rudder, and then make small adjustments in the trim tabs until the boat runs more or less straight while still having the running attitude I need for the conditions and fuel economy. That will improve the autopilot performance quite noticeably. Unfortunately I do not really have the option of not using the trim tabs unless I am going very fast, which is not efficient or comfortable many days.

 

[Magnetron]

Unfortunately I do not really have the option of not using the trim tabs unless I am going very fast, which is not efficient or comfortable many days.

Understandable, but at the end of the day those tabs (in the way they're currently configured), are basically counteracting any adjustments made by our pilot, or any autopilot for that matter, and that's what you're experiencing.

- Maggy

 

[Quitsa]

Unfortunately I do not really have the option of not using the trim tabs unless I am going very fast, which is not efficient or comfortable many days.

Understandable, but at the end of the day those tabs (in the way they're currently configured), are basically counteracting any adjustments made by our pilot, or any autopilot for that matter, and that's what you're experiencing.

- Maggy

You guys seem convinced I have some sort of automatic trim system like the Ziopwakes or Bennett Auto Tab Control. I don't, these are just plain old hydraulic tabs that only change position when I push on the switch. So far as the autopilot control is concerned, once I have made an adjustment and established the tab position, the running properties of the hull do not change. The tabs are not counteracting the steering actions of the autopilot the way an ATC would do.

Probably at some point, autopilots should integrate the pitch and roll data from a sensor such as the SCX-20 into the steering algorithm, which might make a significant improvement in steering performance under a wider array of conditions.

 

[Johnny Electron]

Yes, agreed. I would love to see Furuno package the SCX20 comes with all our pilots rather than the PG700. Hopefully then they could leverage that extra information as you suggest. I have passed the comment to product development because I see how that could be value added. I would say if you are not conducting any adjustments to the trim tabs at all during pilot operations then the learning would account for some of the impact but it depends on the install. There are some boats where the rudder is so small and it is like trying to steer a bathtub and the trim tabs can contribute to those complexities. Slow solenoids, old hoses that bulge when pressurized, slop in the steering, and many other things can lead to higher deadband which also leads to "S"ing or sloppy steering in pilots. It is good you don't have automated tabs because that is also a big issue when trying to run a pilot of any brand. Knowing you on this forum, if anyone can tweak it out; you can.

 

[backman]

Came to this forum for something else but couldn’t help comment on this.

My boat is a Single engine downeast with a barn door rudder, no tabs. The Nav function on the 711C is perfection on my boat.

If I run at 20 knots cruise I set a waypoint 60 to 80 miles out and never see the XTE be more Yards throughout the journey. Even with a cross sea the adaptive algorithm figures things out and my wake stays straight.

The best however is when I do one of my overnight 8 knot chugs , going that same 80 miles over 10 hours.. Even in sloppy sea conditions we rarely see more than a 5 yard cross track error and the autopilot doesn’t over correct.

The only place it gets remotely confused is in some of our high current passages and channels with a wind against tide condition at which point I move to Auto mode so it tracks straight.

Super impressed.

 

[Quitsa]

Came to this forum for something else but couldn’t help comment on this.

My boat is a Single engine downeast with a barn door rudder, no tabs. The Nav function on the 711C is perfection on my boat.

If I run at 20 knots cruise I set a waypoint 60 to 80 miles out and never see the XTE be more Yards throughout the journey. Even with a cross sea the adaptive algorithm figures things out and my wake stays straight.

The best however is when I do one of my overnight 8 knot chugs , going that same 80 miles over 10 hours.. Even in sloppy sea conditions we rarely see more than a 5 yard cross track error and the autopilot doesn’t over correct.

The only place it gets remotely confused is in some of our high current passages and channels with a wind against tide condition at which point I move to Auto mode so it tracks straight.

Super impressed.

If I am running at displacement speed or a little above in that same 8-9 knot range, my 711C will also track perfectly and never show XTE when steering to a waypoint of more than a few yards. But I would also have the trim tabs fully retracted at that speed and in any case, the would have little effect even if deployed. The course deviations issue only manifested itself at 25-30 kts with the trim tabs deployed. With the switch to the manual response, I now see excellent tracking at higher speeds too. I think the trim tabs are changing the steering characteristics of the boat enough to make the "self-learned" response incorrect and created a kind of bad feedback loop.

My boat is probably more of a challenge than most. Not only is she quite light, because of the large fuel capacity and the significant change in displacement between light tanks and full tanks, the trim tabs needed to be large enough to provide lift when fully loaded. Thus they do have more steering effect than typical.