1sailor

Compass headings on board comparison

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Which compass do you believe on board ?    The other day I had 10 of 'em lined up, trying to navigate some tricky reefs in Belize, some very mixed results !

   
Chartplotter   358*
Autohelm digital 358*
Motion-X GPS 352*
iPhone compass 0*
handheld puck compass 352*
Boat magnetic compass 353*
Navionics on phone 353*
Garmin 76 handheld GPS 003*
garmin watch 343*
   

 

 

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Probably would have been better with just one and a good set of polarized sunglasses...where in Belize....I sailed the Yucatan coast into Belize late 70's ~early 80's 4 times...

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51 minutes ago, 1sailor said:

Which compass do you believe on board ?    The other day I had 10 of 'em lined up, trying to navigate some tricky reefs in Belize, some very mixed results !

   
Chartplotter   358*
Autohelm digital 358*
Motion-X GPS 352*
iPhone compass 0*
handheld puck compass 352*
Boat magnetic compass 353*
Navionics on phone 353*
Garmin 76 handheld GPS 003*
garmin watch 343*
   

 

 

plotter and autohelm are factoring in current , the garmin watch is VERY slow to read accurately.....the handherld puck, boat's compass are prolly the closest ( the handheld puck is not getting and magnetic deviation due to other electromagnetic sources....when was the last time you had you boat compass checked?   How about Magnetic variation in Belize? 

 

Belize City 
Latitude: 17° 28' 60" N
Longitude: 88° 10' 60" W
Magnetic declination: -0° 40' 
Declination is NEGATIVE (WEST)
Inclination: 46° 10' 
Magnetic field strength: 39150.0 nT

 

 

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59 minutes ago, SailBlueH2O said:

Probably would have been better with just one and a good set of polarized sunglasses...where in Belize....I sailed the Yucatan coast into Belize late 70's ~early 80's 4 times...

copy that, the cruising guide was nearly useless and the "chart" would work better as a placemat at a low end seafood restaraunt.

eyeball navigation indeed.  Never saw a single nav-aid the entire week..

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Agree Autohelm and chart plotter showed COG including current influence.

Boat compass and handheld showed the direction the bow was pointed.

The rest?  Meh

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1 hour ago, Shenanigan77 said:

Agree Autohelm and chart plotter showed COG including current influence.

Boat compass and handheld showed the direction the bow was pointed.

The rest?  Meh

Don't necessarily go with this. 

Autohelm readout will normally be Heading from a fluxgate.

Chartplotter readout will be clearly labelled HDG or COG.  Presumably OP didn't mistake COG for HDG.

Chartplotter and Autohelm are either driving off the same fluxgate or are equal by accident. 

Mag Variation/Declination is negligible so discrepancies between boat's fluxgate(s) and magnetic compasses (ship's and handheld) are likely due to ship's magnetic effect. 

If ship's compass has been swung "recently " rely on that, noting consistency with handheld. 

Garmin handheld GPS has no fluxgate and can only show COG, may be wrongly labelled HDG.  This relies on direction of travel of the device, and may be inaccurate if device and boat are stationary.

Garmin GPS also have settings to choose between True and Magnetic display AND choose between Auto and Manual Variation setting.  If Variation was manually set to > 0 that also could introduce error in reading.

Remaining devices AFAICS are also GPS based reading COG. 

Coincidence between Motion  X and Phone Navionics and compass would be a happy if reassuring coincidence.

Maybe you should go out and swing your fluxgate(s) against ship's compass.

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5 hours ago, 1sailor said:

Which compass do you believe on board ?    The other day I had 10 of 'em lined up, trying to navigate some tricky reefs in Belize, some very mixed results !

   
Chartplotter   358*
Autohelm digital 358*
Motion-X GPS 352*
iPhone compass 0*
handheld puck compass 352*
Boat magnetic compass 353*
Navionics on phone 353*
Garmin 76 handheld GPS 003*
garmin watch 343*
   

 

 

Give a man a watch and he knows what time it is. Give him two and he has no idea. (aka Segal's Law)

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TRUE

VARIANCE

MAGNETIC

DEVIATION

COMPASS 

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13 minutes ago, SCANAS said:

TRUE

VARIANCE

MAGNETIC

DEVIATION

COMPASS 

True

Virgins

Make

Dull

Companions

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On 4/6/2018 at 8:03 PM, Brass said:

Don't necessarily go with this. 

Autohelm readout will normally be Heading from a fluxgate.

Chartplotter readout will be clearly labelled HDG or COG.  Presumably OP didn't mistake COG for HDG.

Chartplotter and Autohelm are either driving off the same fluxgate or are equal by accident. 

Mag Variation/Declination is negligible so discrepancies between boat's fluxgate(s) and magnetic compasses (ship's and handheld) are likely due to ship's magnetic effect. 

If ship's compass has been swung "recently " rely on that, noting consistency with handheld. 

Garmin handheld GPS has no fluxgate and can only show COG, may be wrongly labelled HDG.  This relies on direction of travel of the device, and may be inaccurate if device and boat are stationary.

Garmin GPS also have settings to choose between True and Magnetic display AND choose between Auto and Manual Variation setting.  If Variation was manually set to > 0 that also could introduce error in reading.

Remaining devices AFAICS are also GPS based reading COG. 

Coincidence between Motion  X and Phone Navionics and compass would be a happy if reassuring coincidence.

Maybe you should go out and swing your fluxgate(s) against ship's compass.

Very succinct.  You have to know what the electrons are set to before they are useful, then they are very useful.     Plotter can be set to use fluxgate or not, usually deep in the set-up screens.

Navionics is just dangerous, the loss of gps signal does not always trigger an alarm.  

 

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On a ship, you have to go through the process of making a deviation card.
No sailboat I've ever been on bothered. But there is often a big hunk of iron under the cockpit sole...

 

 

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Fastyacht, I used this program to make one.  It works fine and is simple.  https://www.yandina.com/compass.htm  To the OP, depending on that boat the chartplotter, autohelm were not that far off of the boat compass at 5 degrees. As much of a concern would be how they compare when you make a course change.  Are you trying to follow a paper chart or a chartplotter? 

 

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5 minutes ago, seaker said:

Fastyacht, I used this program to make one.  It works fine and is simple.  https://www.yandina.com/compass.htm  To the OP, depending on that boat the chartplotter, autohelm were not that far off of the boat compass at 5 degrees. As much of a concern would be how they compare when you make a course change.  Are you trying to follow a paper chart or a chartplotter? 

 

Based on the crap charts in belize, I was mostly following what my eyeballs saw.   I was also plotting lines on a paper chart and comparing the "should be" headings (per the paper chart) with the magnetic compass in front of me.  The variance between those and the 9 other mediums I had access to was baffling, which got me thinking... which resulted in this post..

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There might be an incorrect deviation setting in your chartplotter / autohelm or maybe there is a bit of magnetic stuff near their sensor. I'd check the instrument settings and I'd take the handheld puck and walk around the boat to see if it gives different readings in different places. It's always a good idea to swing the boat and run the setup for the fluxgate. I wouldn't worry about the readings from the GPS's that don't have magnetic sensors. They can't give reliable heading readings until you're moving several knots. 

With the handheld compasses you may find that devices that were setup for one hemisphere are a bit sticky when used in the other hemisphere because of dip. Take a close look to make sure that you're getting good readings. I don't suspect that's what's going on here but it's annoying enough that I keep Northern and Southern puck compasses aboard.

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19 hours ago, seaker said:

Fastyacht, I used this program to make one.  It works fine and is simple.  https://www.yandina.com/compass.htm  To the OP, depending on that boat the chartplotter, autohelm were not that far off of the boat compass at 5 degrees. As much of a concern would be how they compare when you make a course change.  Are you trying to follow a paper chart or a chartplotter? 

 

Thank you very much, I'm definitely going to try the mentioned program.

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On 9/4/2018 at 7:58 PM, seaker said:

Fastyacht, I used this program to make one.  It works fine and is simple.  https://www.yandina.com/compass.htm  To the OP, depending on that boat the chartplotter, autohelm were not that far off of the boat compass at 5 degrees. As much of a concern would be how they compare when you make a course change.  Are you trying to follow a paper chart or a chartplotter? 

 

I've tried downloading this program, but get an 404-error. Are you getting this problem as well?

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On 4/9/2018 at 8:19 AM, fastyacht said:

On a ship, you have to go through the process of making a deviation card.
No sailboat I've ever been on bothered. But there is often a big hunk of iron under the cockpit sole...

I have a pair of cockpit bulkhead mounted Danforth Orion compasses on my boat because of tiller steering.  25 years ago I had a professional compass adjuster (most of his work was for the Navy) adjust the corrector magnets, then prepare deviation cards using a sun compass.  It cost about $150 and about 1 hour's time motoring around  the bay.  The starboard compass was correct with only 4 points 1/2 degree off, port had errors of up to 4 degrees East, 2 degrees East over half of the circle.  He couldn't adjust it out, possibly the cause was a Telcor Selsyn technology apparent wind readout near the port compass, or a lubber's line misalignment.

So the starboard compass is the standard compass, and the port compass is a steering compass.  Years later I installed a TackTick Race Master  on centerline above the companionway; it matches the starboard compass 100% when the deviation card corrections are applied to the starboard compass.  Unfortunately, it no longer works at night, dead battery.:(

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18 hours ago, MikkelPetersen said:

I've tried downloading this program, but get an 404-error. Are you getting this problem as well?

I am sorry to say I have not used it recently.  Just now when I tried to download it I also got the error message.  It has the basic program written out so you may be able to copy and paste that into a program that can run basic.  I couldn't find another program or a app that does the same thing.  Good luck

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2 hours ago, seaker said:

I am sorry to say I have not used it recently.  Just now when I tried to download it I also got the error message.  It has the basic program written out so you may be able to copy and paste that into a program that can run basic.  I couldn't find another program or a app that does the same thing.  Good luck

Thank you, but what a shame. I'm not really an IT-geek.

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11 hours ago, seaker said:

I am sorry to say I have not used it recently.  Just now when I tried to download it I also got the error message.  It has the basic program written out so you may be able to copy and paste that into a program that can run basic.  I couldn't find another program or a app that does the same thing.  Good luck

The Wayback Machine to the rescue: https://web.archive.org/web/20061209070300/http://www.islc.net:80/~yandina/COMPASS.EXE

Hopefully it doesn't have any diseases...

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at the end of the day i only care about where the airplane or boat is going over the ground, so i navigate off of COG (or TRK in airplanes), but i steer off of the compass/DG. Relative numbers are good enough - just gotta make sure the vessel is actually going to end up where i want it to. I'll take the COG/TRK of the fastest updating device, ie: whatever is hopefully running WAAS, and steer off of whatever is most convenient to see and is providing the best steering. 

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A man with a compass always knows where he's going, a man with two is never sure. Now 9 sources of information, he better lie down and take a zanex....

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Charts are pretty worthless in Belize. Polarized glasses are a must. Charts are just loose ideas of whats where. As for no navigational aids? Thats bs! I saw a few twigs poked in the ground to mark through a channel. To be fair it was just one side but still!

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On 4/6/2018 at 5:55 PM, Shenanigan77 said:

Agree Autohelm and chart plotter showed COG including current influence.

 

it depends what he chose to display..., a plotter is perfectly capable of displaying heading.., and so is an autopilot control display...

but - when he refers to "Autohelm digital".., I think he might be talking about one of the handheld electronic compasses that were sold under the Autohelm brand - 

autohelm-raytheon-electronic-hand-bearin

so that would not be displaying COG

with respect to some of the others  - the garmin and the iphone apps - both devices have electronic compasses.., so might be displaying heading, or might be displaying COG.., depending on what is selected - presumably.., he selected compass heading

one thing about all the handheld devices - it's really difficult to line them all up exactly the same.., so i could easily see a few degrees difference just because of that.

I am guessing that by "boat magnetic compass" he means an analog compass - so we don't know if it was compensated and has a table..

likewise with the boat electronic compass that feeds the plotter- is the fixed offset correct.., and was the calibration done recently. even if that is done.., it is still just like compensating an analog compass in that there will always be some residual deviation that can't be calibrated out. 

i am not really sure what to make of this comment;

On 4/6/2018 at 4:06 PM, dacapo said:

he handherld puck, boat's compass are prolly the closest ( the handheld puck is not getting and magnetic deviation due to other electromagnetic sources

but if the intent is to say that the puck and other handheld devices are not affected by the local magnetic field created by the boat - this is not correct...

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56 minutes ago, us7070 said:

it depends what he chose to display..., a plotter is perfectly capable of displaying heading.., and so is an autopilot control display...

but - when he refers to "Autohelm digital".., I think he might be talking about one of the handheld electronic compasses that were sold under the Autohelm brand - 

autohelm-raytheon-electronic-hand-bearin

so that would not be displaying COG

with respect to some of the others  - the garmin and the iphone apps - both devices have electronic compasses.., so might be displaying heading, or might be displaying COG.., depending on what is selected - presumably.., he selected compass heading

one thing about all the handheld devices - it's really difficult to line them all up exactly the same.., so i could easily see a few degrees difference just because of that.

I am guessing that by "boat magnetic compass" he means an analog compass - so we don't know if it was compensated and has a table..

likewise with the boat electronic compass that feeds the plotter- is the fixed offset correct.., and was the calibration done recently. even if that is done.., it is still just like compensating an analog compass in that there will always be some residual deviation that can't be calibrated out. 

i am not really sure what to make of this comment;

but if the intent is to say that the puck and other handheld devices are not affected by the local magnetic field created by the boat - this is not correct...

The original Autohelm handheld compass was notoriously sensitive to the angle at which it was being held:- a lateral tilt of say 10 degrees would result in alarming differences in displayed compass bearing.

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3 minutes ago, lyvet said:

The original Autohelm handheld compass was notoriously sensitive to the angle at which it was being held:- a lateral tilt of say 10 degrees would result in alarming differences in displayed compass bearing.

I have one - I find that I get pretty repeatable results with it.., so it's pretty good for monitoring the bearing to competitors

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Posted (edited)
24 minutes ago, us7070 said:

I have one - I find that I get pretty repeatable results with it.., so it's pretty good for monitoring the bearing to competitors

Next time you use it, try tilting it to the left and right. It basically has the same fluxgate sensor as in the old AH pilots but of course, they were gimballed.

In flat conditions the AH hand-held compass was fine but it was very confusing in rough conditions. I use my old faithful Mini-Morin https://www.starpath.com/catalog/accessories/HP2.htm

I also have a KVH Datascope but it isn't brilliant-the display started "bleeding" and became blurred. Not good for a relatively expensive piece of equipment.

Edited by lyvet
Addition/clarification

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On 4/6/2018 at 7:40 PM, MelbourneA31 said:

True

Virgins

Make

Dull

Companions

Add Whiskey.  (West corrections + in that direction)

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6 hours ago, Soley said:

A man with a compass always knows where he's going, a man with two is never sure. Now 9 sources of information, he better lie down and take a zanex....

i bet i could hit a layline with 9 compasses. 

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1 hour ago, condor said:
On 4/6/2018 at 4:40 PM, MelbourneA31 said:

True

Virgins

Make

Dull

Companions

Add Whiskey.  (West corrections + in that direction)

255l_large.jpg

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I believe the one at the helm.  Mine is a 6" Ritchie with a recent calibration card.

At your latitude, there shouldn't be too much discrepancy.  

You listed 353 magnetic.

I'd stick with that regardless of what electronics tell you (unless of course your compass, and/or your electronics are all 'effed up...

Also, it never hurts to shut down, and reboot the iPhone once in a while...

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3 minutes ago, SailNDive said:

 

Interesting thought that Navionics is dangerous because of GPS signal not triggering an alarm.  Most people use Navionics chips in their chartplotter. Navionics gives you the chart data. Alarms and other actions are usually part of the chartplotter software, fyi

 

i think from the helm was referring to the navionics app on iphone, or whatever - and not to a plotter loaded with the charts

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On 4/17/2018 at 12:54 PM, SailNDive said:

 

Interesting thought that Navionics is dangerous because of GPS signal not triggering an alarm.  Most people use Navionics chips in their chartplotter. Navionics gives you the chart data. Alarms and other actions are usually part of the chartplotter software, fyi

 

Correct, I was referring to an experience from last year using iPad for chartplotter, never again.  

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