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-   -   Running autopilot without magnetic reference (https://www.cruisersforum.com/forums/f13/running-autopilot-without-magnetic-reference-226787.html)

jamiehc 20-11-2019 10:02

Running autopilot without magnetic reference
 
Planning on sailing the high arctic with Raymarine ST6001 auto pilot. The proximity to magnetic north means there will not be reliable direction from the fluxgate compass. Most heading sensors still use magnetic north. I have looked into a satellite compass (SI-TEX Vector 3D Compass) which uses differential GPS to give a heading but it is unclear if the heading data generated would be readable by the Raymarine thru the fluxgate input. Any suggestion?

Pete7 20-11-2019 10:07

Re: Running autopilot without magnetic reference
 
how far north are you going 70'N ?

Pete

jamiehc 20-11-2019 11:17

Re: Running autopilot without magnetic reference
 
Furthest north would be Resolute 74.68 if ice permits. 74.68

Pete7 20-11-2019 14:30

Re: Running autopilot without magnetic reference
 
Well that's about the limit isn't it. Anyway I asked a similar question and Evans answered it here in post 218.

https://www.cruisersforum.com/forums/...ml#post2563661

Brian.D 20-11-2019 20:26

Re: Running autopilot without magnetic reference
 
Every location on earth should have a representative compass rose, with the except or 90 North Latitude (which every direction is 180) and 90 South Latitude (which every direction is 0). So, therefore, using a GPS in lieu of a magnetic compass should afford you good bearing. "Should" being the operative word.

smac999 21-11-2019 02:41

Re: Running autopilot without magnetic reference
 
I doubt that old pilot is going to accept a heading from anything else.

I would think a pilot would still hold a straight course. you just maybe won't be able to use it to navigate to a correct bearing. IE stick 10 degress in the pilot and it will hold you straight, it just may not be actually 10 degrees. going to a waypoint should still work.

Pete7 21-11-2019 03:30

Re: Running autopilot without magnetic reference
 
I would ask Bob Shepton, who has sailed Dodo's Delight up there frequently.

Skipper & Delivery Services by Bob Shepton - Home Page

Some fun You tube videos of his exploits too.

Isn't the magnetic N pole moving rather rapidly at the moment too, just to add to the fun.


Pete

CarinaPDX 21-11-2019 12:23

Re: Running autopilot without magnetic reference
 
I am not familiar with the devices involved but the process to find compatibility is simple enough. First, what is the output of the compass? NMEA 0183 or 2000? If so, the which sentence (HDG, HDM, HDT, other) or PGN (127250?) is output? Knowing that, does the autopilot accept that sentence or PGN? If not, is there a converter available to do the job? The information will be in the spec sheets and manuals.

Greg

billknny 21-11-2019 12:38

Re: Running autopilot without magnetic reference
 
The problem is not the variation, it is the "dip" The lines of magnetic force become near vertical near the magnetic pole. This does not only affect your electronic compass, but your steering compass as well. Few compasses can handle a significant change in "dip" from what they were designed for. Taken outside that range the card tilts, and jams.

Check the specs on your steering compass...What Zone was it designed for? And what Zones will it work in? Or maybe you're lucky and it is a world wide compass...

Or maybe nobody else uses a steering compass anymore...

AndyEss 21-11-2019 12:57

Re: Running autopilot without magnetic reference
 
The fluxgate input on that old ST6001autopilot (300 course computer?) is proprietary.
Keep the old fluxgate in place, and use a modern MFD for setting courses via dGPS

CarinaPDX 21-11-2019 14:17

Re: Running autopilot without magnetic reference
 
RM used that mediocre flux gate compass for years, and it had a 5 (?) wire analog input, which is not great. Later RM autopilots would use heading input over the bus in preference to the RM fluxgate, if available. Since RM reused the same product name over the years you would have to check the manual for your version. If it can use a SeaTalk-connected input it should be able to use an external compass but probably requires a converter if so.

I am not familiar with the 6000 series but the ST2000 and ST4000 names covered several generations of products. It is confusing to customers, retailers, and service people alike, and misses the opportunity to highlight new products. Any product manager who does that should be run out of town on a rail...

Greg

Breaking Waves 21-11-2019 14:51

Re: Running autopilot without magnetic reference
 
the first question is whether the autopilot can take NMEA heading input? Some generations of that unit clearly can.

If so, it will be (relatively) straightforward as most of the sat compasses and inertial compasses (your two hardware options) are able to output NMEA.

If it can't take NMEA, then you will need a converter box, which I know nothing about - I personally would rather get a new autopilot than mess with that.

captainjim47 24-11-2019 17:30

Re: Running autopilot without magnetic reference
 
depending on where you look Mag North is 72.62W longitude and 80.31N latitude, currently... it has moved dramatically south recently. I spent a few months at, around and above the N60'th never did catch the vessels compass spinning around and GPS track stayed quite reasonable...

RaymondR 24-11-2019 20:52

Re: Running autopilot without magnetic reference
 
I think the ST series all used the same head and you told it which model it was in the Dealer Setup mode.

Also I think CarinaPDX is right about the fluxgate.

I also suspect that it will work OK pretty far north as long as there is still some sort of directional information as long as the lines of force aren't vertical, be interesting to find out what the limit is.

The fluxgate is mounted on a gimbal and the cover is removable. You could experiment by accessing and tilting the fluxgate and watching the heading indicated on the head readout to find what the limit is.

Interesting question which I'm feeling to lazy to research at the moment. Does the field strength at the poles increase significantly because of the converging lines of magnetic force? Logically it would. If so will the increase in field strength assist the fluxgate in defining the direction of the lines of force?

captainjim47 26-11-2019 18:06

Re: Running autopilot without magnetic reference
 
while a sufficiently artful programmer can certainly achieve the appearance of a straight line on an MFD... a GPS based steering compass actually requires a GPS system capable of something approaching a 20Hz update rate. ya, that seems excessive but one of the justifications for an A/P is the non-trivial fuel savings in actually spending all of your time traveling in precisely the direction you want to go, not just some of the time. The ublox NEO-M9N is up to 25Hz on all SAT POSIT systems... I'd be surprised to find one in a Ray A/P as it is far cheaper to use one of the many geophysical sensors which are incredibly cheap now due to SAMSUNG's use in practically every cell phone they sell whether advertised or not... Apple, not so much. BTW, for all the flat earthers and other conspiracy theorists... the 9 even has spoof and jam detection. https://www.u-blox.com/sites/default...9027207%29.pdf


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