st 4000 + compass deviation problem

[philwsailz]

Sorry, let me hijack the thread slightly.

Let me remind everyone that while a GPS is good at telling you where you are to some reasonable precision, GPS signal alone cannot tell you your heading. Global Positioning System, not Global Heading System... Even under way, a GPS device will tell you your course over ground as a compass bearing, but it will not tell you where your bow is pointed. Consider backing in reverse as a simple example of where the GPS bearing will differ wildly from an adjacent magnetic compass. Also consider traversing a current, or pointing/pinching high while slipping, where you have adjusted your heading to correct for the external factor to give the COG you desire.

Flux-gate, or traditional, a compass is going to be affected by any ferrous materials in reasonable proximity that can affect the way the magnetic flux field intersects the compass. When you move ferrous materials about on a boat you will affect the compass reading... To what extent is dependent on many factors, size, relative location, distance, etc. This is why even a simple magnetic compass has a mechanical/magnetic means of correcting for actual mounting, to compensate for the effect of other magnetic or ferrous materials onboard.

As a loudspeaker provider to the marine induistry, I am keenly aware of what happens when you introduce magnetic materials or potentially magnetic materials to a boat....

"Sir, why regardless of which way I steer does the compass point due south? It is warm; I know we are not at the North Pole..."

 

[Stu Jackson]

Thanks, Phil for that great description which differentiates heading (bow pointing) from course. I hadn't thought of the going bassackwards before, very good. I usually use the "boat's in a river, current going west, bow pointing north" example. Still and all, a lot of skippers don't get it.

 

[philwsailz]

Thanks, Phil for that great description which differentiates heading (bow pointing) from course. I hadn't thought of the going bassackwards before, very good. I usually use the "boat's in a river, current going west, bow pointing north" example. Still and all, a lot of skippers don't get it.

I have two metal hips, with rods in my femurs that go almost to my knees. I realize based on this thread I might need to be nervous about how my tiller pilot is going to work.... I am going to laugh my backsides off if I am unable to set it and then go forward without affecting the flux-gate compass in the thing.... or am able to dance around on the decks to change tiller-pilot heading...

Hopefully my prosthetics are of the ferrous-free low-carbon variety...

 

[mortyd]

a little knowledge of navigation is a dangerous thing. gps is a miracle. people who make their living navigating have absolutely no conversation on this topic. some people like to hunt with bow and arrow, some like to send smoke signals, or heat their houses with wood, and that's fine. but don't use lack of knowledge of gps and how to use it as an excuse to back two centuries. all in good spirit ok? i learned to navigate with vhf and am radios and we thought that was wonderful. now it seems totally antique. gps is your friend, welcome it.

 

[mortyd]

phil, reasonable precision? do you write campaign speeches? it gets me within inches of my mooring. forget bearings and candle wicks, just do like pilots do and follow the dot. none of this says you should through away your charts. no gps knows where the rocks are.

 

[philwsailz]

Don't get me wrong Morty, I love GPS, but I understand its limitations. To trust it blindly without a means of checking to see if it is close or ridiculously off is just not prudent. That is what a good old fashioned compass will do for ya.

I am not here to argue, I will tell you though that a GPS once told a driver I was riding with to rurn right as we were starting to cross the Brooklyn Bridge.... They cannot tell direction nor can they tell elevation...

GPS is not infallible.

 

[mortyd]

gps didn't tell him anything. all gps can tell you, with staggering accuracy is where you are. nothing more. no roads, no bridges, no rocks. just where you are. when i first got my boat i went to the coast guard auxiliary for an advanced WATER navigation and pilotage course and they insisted i take the beginning course first. i then showed a comercial pilot instructor license, and they said it meant nothing - it was for an airplane. somtimes, including for me, it's time to listen.

and if you don't trust gps 'bindly' i seriously suggest you avoid commercial aircraft.

 

[Stu Jackson]

I have two metal hips, with rods in my femurs that go almost to my knees. I realize based on this thread I might need to be nervous about how my tiller pilot is going to work.... I am going to laugh my backsides off if I am unable to set it and then go forward without affecting the flux-gate compass in the thing.... or am able to dance around on the decks to change tiller-pilot heading...

Hopefully my prosthetics are of the ferrous-free low-carbon variety...

Phil, NOW I know how we get along so well: I got one of those plates in my left femur. I guess my AP is doing OK since it's on the starboard side of my cockpit!

My plate hasn't triggered the detectors at airports, so i guess we might be OK after all!

Mine is titanium. Actually my first and second were and are titanium. How the first one broke is still beyond me.

Maybe we should get T shirts: FEMURS FOREVER.

I'm sure mortyd was the first kid on his block with a Model T and a color TV. Personally, I'll take a horse and book any day!

 

[mortyd]

no, stu, my father was. if you send me your email address to mortyd@nyc.rr.com i will tell you what the late admiral alan shepperd said somewhat involving sailing, definitely x-rated, so no minors.

 

[Tom J]

don't get on a commerial airliner unless you bring a compass in case the batteries all die at once also, bring an astrolabe in case you go throuigh magnetic anomaly. and, don't forget a grammophone and cabon paper, just in case....

Most airliners land themselves. Maybe we should just forget about the pilot, too.

 

[mortyd]

tom j, there's a current pilot joke that every new jet comes with a gps, a pilot and a dog. the dog is there to bite the pilot if he touches anything.

 

[philwsailz]

and if you don't trust gps 'bindly' i seriously suggest you avoid commercial aircraft.

Not gonna do it. Here's why:

I thought about this overnight, and while GPS might be a sole aid for position for a plane, I believe I can make some points suggesting why it is appropriate for flying yet probably inappropriate for sailing or boating.

* Per my previous analogy comparing GPS and compass headings, commercial aircraft cannot fly backwards.

* if a commercial airplane is sitting still or moving slowly where GPS cannot get a heading it will usually indicate the location also coincides with an airport

* you have radar, two way radio, and I have to believe a couple of redundant collision avoidance mechanisms that while don't give heading or location at least try to prevent you from running into other solid objects in your path.

* Air Traffic Control: a commercial pilot has someone looking over his shoulder most of the time in case positioning equipment fails. A commercial pilot has someone who can talk him down if the GPS totally quits. The sailor doesn't.

My apologies to the OP for this thread hijack regarding his autopilot. I do hope this paints a more fair comparison between a commercial plane following what amounts largely to a prescribed highway in the sky and a solo sailor trying to get from point a to point b. The redundant systems are different, but redundant systems are necessary. To rely solely on GPS to get you home while on a boat is risky, if not downright foolish.

Your argument otherwise suggests both positions are simply opinion. I believe differences of opinion foster fun and engaging conversation, so to you, a pleasure visiting!

 

[mortyd]

phlogiston.

 

[philwsailz]

Hope someone can help me with this. I recently bought a 97 c250 with wheel.....and st4000 installed. When I engage the auto pilot it will not hold a course. I read the book and tried to drive in circles to adjust the compass deviation. I engaged the clutch, hit standby and paged to the swing. Went around in circles for about 15 minutes but the unit would not adjust. The deviation reads 0.

Am I doing something wrong or is there a mechanical problem. Supposedly the prior owner never had a problem.

Any suggestions would be appreciated

Back to the OP.

I am not a user of your wheel pilot, but I have studied the ST1000 instructions for the tiller pilot I have installed on my boat, (still in the shop). Based on that familiarity, I went and downloaded the ST-40000 manual.

In addition to tryig to calibrate the compass, you might dig through to the calibration section for Rudder Gain. Start on page 27 if, (hopefully) you have the same manual as what is posted on-line. Check to see if the gain is too high, and the wheel pilot is simply wandering back and forth on either side of your desired heading. The thing could just be over-correcting with each adjustment. If this is the case, adjusting the gain down will provide a more straight-line track on your desired heading.

Also check the auto-trim. It is probable that the pervious owner had a different sailing style with different sheeting angles and heeling comfort. If this is the case, their proper trim level might be different from yours based on sailing preference.

Hopefully it is not a wild goose chase, but I perceive there is a chance that the compass is right on the money, and your perception of not holding a course might be related to other things that can be tweaked.

 

[mortyd]

for those who believe in science, what are you trying to say or codemn? when my gps says i'm going 4.3 knots over the earth how inaccurate is it compared to what you use to determine your speed? when my gps says i'm bearing 67 degrees true, how inaccurate is it compared to your compass? how often do you think the normal two different gps's die at the same time? where did you get your flight training? nothing of what you said has anything to do with gps or how it is used. but you make this point, next time i'm out of sight of land i'll be sure to take my boy scout compass.

 

[philwsailz]

Nevermind.

I don't know why I have kept on other than for sport, but it does a dis-service to the guy who was looking for help with his wheel pilot.

Science fails, sometimes infrequently sometimes often, and man's wrestling attempt to wrestle control over nature often backfires. My favorite example I have studied recently is the Riviera in the Desert, the paradise promised that now languishes as the Salton Sea... Look at how man screwed that one up both by accidentally creating it, and then trying to use technology to bend it to his desires. Go check it out now, it is a lovely place....

Science is awesome and I love GPS; looking forward to using it again if my lake ever refills, (parts of it currently remind me of the body of water mentioned above). Still, I would be scared silly to attempt to go over the horizon without the ability to fall to a backup means of navigation, one provided by celestial bodies that have been there, (or appear to be there) for the history of terrestrial navigation, combined with a magnetic force that exists on this earth pretty consistently.

I know lots of folks have been watching and reading, but now their popcorn boxes and soda cups are empty, and they are chewing on what ice is left wondering if the show will end. To that end I will close my arguments with this thought, borrowing from the great philosopher Buck Dharma, "History shows again and again how nature points up the folly of man..."

Yes, we need more cowbell....

 

[Stu Jackson]

More cowbells...

mortyd's little rant was "tres funni", I'll send it to you, Phil.

...and it should be "...heading 67 true..." 'cuz a bearing is TO a waypoint or other object. Darn manuals...

 

[philwsailz]

mortyd's little rant was "tres funni", I'll send it to you, Phil.

...and it should be "...heading 67 true..." 'cuz a bearing is TO a waypoint or other object. Darn manuals...

Sweet! Looking forward to it!