downeast autopilots at cruise speed

[GLA]

I have a auto nav autopilot . it is run by hydraulic actuators fed to turn on by the computer. with a regulator to increase or decrease hyd flow .

the auto pilot is great up to 12 knts. at cruise speed 16 knts it likes to hunt.
the pilot has all kinds of adjustments. and they are currently all set at a bare minimum. and it still serpentines back and forth. if you increase the settings , regulator ect it only hunts faster. usually 10 degrees left right

the reason seems to be the size of the rudder. the boat is a 42 ft x 13'-6 with a 5 ft draft, northumberland straights style hull, the rudder is 3 ft deep, the slightest turn of the rudder really moves the boat to left or right.

now to my question, does anyone run a different pilot, and are you able to maintain a constant straight course over 15 knts. or is this just a normal issue with a downeast style hull. slightest turn of the rudder moves the bow to quickly. for the pilot to compensate.

 

[djmarchand]

This is not an inherent problem with downeast hulls. Play with the tuning parameters to get it to run straight, gain, etc.

 

[November Rain]

We have a Simrad AP35 and run 15-16 knots, if the setting is not set on high and is on low it will be all over the ocean.

 

[Crabman]

Make sure you don't have any play in your ram connection to your rudder quadrant. Also make sure your rudder is zeroed when running a straight line. I had a problem with my 36 BHM whereby the rudder was at five degrees while trying to go straight. The boat kept searching. Slow speed not too noticeable. Higher speeds it wandered all over. Went to the menu page and zeroed the rudder while holding the boat in a straight line by just hitting the rudder button twice and I had a new autopilot again.

We were shocked how easy this was when we finally found the page and how well it worked this winter running back from the canyons in some real slop. Seems if the rudder is off of zero, the autopilot will search. The further off, the more it will search. The faster you go, the more it will search.

I have a Simrad 28 with the typical downeast power steering and a Marine Hydraulics solenoid. It always worked pretty good but the stern always had a slight wag to it. Once zeroed, it's right on.

 

[GLA]

everything seems tight, the rudder indicator is a couple of yrs old. replacing it did not solve the problem, I center the rudder by going hard over one direction and measuring the hyd cylinder sticking out, then hard over in the other direction and dividing the distance in half.
the newer simrads seem more user friendly , maybe that is the problem
not a good unit.
although two scallopers I know have the same pilot and they love them. yet they only cruise at 8-10 knts and do not notice the higher speed issues

 

[Raider Ronnie]

My BHM 28 runs great 12-14 kts on auto pilot.
I can just sit back and relax at the helm seat and watch my screens.
Unless it's like glass conditions anything over 14 kts it's like a snake !
Straight into a head sea it's best. Anything from the side-stern, a snake.
I've played with the response settings and it makes no difference.

 

[Blacktide]

I get the same thing in a following sea . My NB 36 zig-zags all over. I ve played with adjustments a few times, ill play around with it next time out.

 

[Crabman]

Just to be clearer, what does your rudder indicator read when you are going in a straight line while hand steering, no autopilot? Is it off zero, on the indicator, while holding a straight line? If it is, it needs to be adjusted. Once I got the rudder reading zero while hand steering, it held course to a cruise speed of 17.5 kts without a problem with the autopilot on.

 

[GLA]

while underway, the pilot indicator is at 0 when going straight ahead

seems to be positioned right with the rudder

if you had a 36 bhm going straight, don't see why I can't get this one to track

 

[Rds85]

I have a different configuration, Simrad AP 22, but if you have the rudder straight, and the autopilot is in "high", you might try to crank the yaw sensitivity down to one degree. The autopilot will work more, maybe too much, but it will tell you if the autopilot can steer your type of boat straight.
As someone else suggested, watch the rudder angle, the autopilot course vs. actual, etc. while it is working. You may see something there.

 

[backman]

Won't an autopilot heading on a single engine always be a few points to port to counter the prop?

 

[Tmccar1]

Can't speak to your specific unit but I've got a 45' Northumberland style and I haven't had issues with the auto pilot keeping course. Like others have said, I don't think it's a hull specific thing.

 

[Crabman]

Won't an autopilot heading on a single engine always be a few points to port to counter the prop?

I'm not sure. I had a real tough time with the wandering. I made sure the hardover to hardover time was within limits. (I had to turn down the pressure on the solenoid). I ran the boat for a couple of months and was not thrilled with the handling and wandering. I read in the manual about zeroing the rudder after noticing while in gear going straight would take a few degrees of left rudder but once the autopilot sensed we were going straight it zeroed the rudder on the indicator and the boat wandered. I handheld the boat in a straight line, saw the rudder indicator was a few degrees left, went to the menu page hit the rudder button twice and the rudder indicator centered while hand steering. Turned on the autopilot and it was like a different boat. I was amazed.

With all this in mind, I had to first tighten up all the loose slack in the steering system. Before doing this, hand steering was tough due to wandering from the slack. For an autopilot, it was impossible to hold a decent course at any speed, especially high cruise speeds. Removing the slack helped a lot. Turning down the pressure to the solenoid also did a lot. With the pressure high, the boat responded too quickly and too hard. Finally, zeroing the rudder brought the autopilot to a new level of control. We all were amazed.

I hope you guys can find what it takes to get your autopilot under control, it sure makes the trip a lot more enjoyable.

 

[greg]

Not enough info to comment.

Does your unit have a rudder feedback indicator?

Does it have a rate gyro compass or do you get heading from gps?

What parameters does it have for how often it compensates for deviation?

How many turns does your wheel have post to post?

Usually, the AP's will all have an adjustment for how often it changes your heading based on heading. If you set it too small, your pump will be running all the time and you can get into huge swings as it tries to establish a heading. This can be an issue on DE's with a lot of turns post to post. The AP will overcorrect and then the error starts to feed on itself.

Too slow and you will drift back and forth along your rhumb line (lazy stearing).

Another issue you can have is if you are using an electronic compass for heading, it can get interference from other sources and throw your heading off. If its too close to your alternator for example an increase in speed could begin to cause more interference which throws your course off.

Lots of variables.

I've got a garmin ghp-10 and it holds very well. It has an annoying deviation on certain headings which doesn't effect my course but does throw my displayed heading off, Just haven't had time to track it down.

 

[GLA]

80% better

into the settings again and I made an adjustment to the rudder travel. manufacturer recommends 35 degree setting.which I never moved from the beginning, means the rudder will correct up to 35 degrees left or right to stay on course. so I moved the setting to 15 degrees. bingo, boat doesn't wave as far. then on the run home I kept decreasing the rudder angle down to 10 degrees and the boat tracks almost straight. it still wiggles a little, but no where near what it did before.

a joy to run now. hope it lasts.

ride out at 15 degrees was in smooth seas, ride home was 2-4 ft quartering off the port transom. ran like a new girlfriend.

 

[Northern bay]

I run a simrad ap28 with solenoid on my NB38 and it's dead straight no matter what the sea. Just ran to and from my home port to Montauk 170nm at 21knots and was never more than .001 off course. Keep tweaking it until dialed in right. Be sure to write down your settings.

 

[Brooksie]

Yes, zero in you angle indicator when you are running straight ahead at speed, not when the rudder is centered on the boat.

Then look to your gain adjustment which usually needs to be turned down, not up, to control essing.

Usually if she won't hand steer good at a given speed, the AP won't steer her well either. Then you must look to the rudder itself. Usually the primative flat plate with shaft down it will cavitate after a certain speed and the helm must keep turning back and forth to "touch" solid water on each side. When it does it over corrects and must be turned back through the void only to over correct the other way. Add a wedge to each side at the trailing edge to test this out first then buy/make a wedge shaped rudder which is the proper shape for higher speeds anyway.

 

[GLA]

angle indicator and straight running have always been good. when indicator is at zero, I am steering straight. the problem was that the computer has a setting for rudder travel. what I believe was happening before was the rudder was going over 35 degrees at every correction to course and continuing that routine back the other way. now that I am limiting the rudder movement it is better.
this may be a different pilot than you have. machine was made in canada
called auto nav.
although pilots pretty much all work the same way.

boat steers great at any speed. I do not believe that I have any cavitation in the rudder.

thanks for the help

 

[Brooksie]

GLA, Glad your AP problem solved; can't be without it on long runs...