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Help Please with Compass Adjustment

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Created by Rob S > 9 months ago, 22 Nov 2017
Rob S
VIC, 391 posts
22 Nov 2017 9:58PM
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Can anyone tell me what I am doing wrong with my magnetic compass adjustment procedure?

Here is the pre work to calibrate the auto pilot:

1Executed the compass calibration procedure for my Raymarine auto pilot. EV core sensor (3-axis digital accelerometer | 3-axis digital compass | 3-axis gyro digital angular rate sensor)
2Adjusted the compass reading on the chart plotter to compensate for a one degree error in heading due to a core sensor installation alignment error.
3Use my laptop based Navigation Planner software to prepare a route file between two points on Lake King exactly aligned with Magnetic North. (True North plus 12.9 degree declination)
4Set preferences in chart plotter to display magnetic compass direction.
5On a calm day at slack tide, set the autopilot to follow the track to confirm alignment and calibration steps. Rock solid on 000 degrees M for several minutes.

I've tried a couple time to adjust out the errors in my backup Ritchie magnetic compasses mounted at each helm. I am not happy with the result. The deviation charts don't look normal. I am not sure if it's a fault in the logic of my procedure or error caused by the need to remove the compasses from their mounting position and re fit every time I adjust the N/S or E/W adjuster. Here is the procedure:

1Use the auto pilot to follow the magnetic North heading route. Adjust all error out using a brass screwdriver in the N/S adjuster.
2Use the auto pilot to follow the magnetic East heading route. Adjust all error out using a brass screwdriver in the E/W adjuster.
3Use the auto pilot to follow the magnetic South heading route. Adjust out half the error using a brass screwdriver in the N/S adjuster.
4Use the auto pilot to follow the magnetic West heading route. Adjust out half the error using a brass screwdriver in the E/W adjuster.
5Swing the compasses to produce the deviation charts.

Ritchie Compass............. 00 30 60 90 120 150 180 210 240 270 300 330
Raymarine Magnetic .... 354 24 54 85 117 149 179 209 237 265 294 324

FabulousPhill
VIC, 261 posts
23 Nov 2017 8:22AM
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I am not familiar with all your electronic nav, but I have tried to adjust my magnetic compass (and made a compass deviation table) and the autopilot compass without success. My autopilot would not 'learn' from doing the slow circle, being a steel boat, perhaps the present yacht also from memory.

First things first: your table above comparing the Ritchie compass and the Raymarine Magnetic are only 6 degrees maximum out of synchronism, so it is not a huge problem in the real world. On Lake King and inland, it is not an issue. Out at sea it is a minor issue. Hand steering also has an error of 6 degrees or so, or more.

I have the Simrad tillerpilot which has no digital display of what the heading is. The heading is where we are going. It is a matter of (lakes) point to that headland and press 'auto'. Out at sea the procedure is steer the yacht to where the handheld GPS says we are aiming for, (Wilson's Prom), and then press 'auto' on the tiller pilot. Whether it is 270 degrees or 265 degrees is not important. With the tide and leeway, the autopilot will get a new instruction from me after a while, after ten minutes or after 4 hours.

The compass and the autopilot/tiller pilots are servants of mine, they steer for me. I need to adjust the heading to take into account leeway (especially traversing the coast, the 90 mile beach), and I will plot on the paper chart from the handheld GPS. If the tiller pilot or compass are slightly incorrect, then I will know that from comparing it to the HH GPS. It's not a big problem, this imperfect calibration.

MorningBird
NSW, 2643 posts
23 Nov 2017 9:28AM
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It is possible/likely that your location has its own magnetic variation. When we use to compass swing our Navy aircraft we used a known magnetic neutral area. It wasn't uncommon to have a degree or two error on other parts of the airfield.
IT is also possible/likely that you boat's head is not pointing directly along the chart plotters track. Under motor there will be some torque effect causing the boat to be pointing slightly off the boat's track through the water.
Your compass won't be a military grade item. If it is within 5 degrees the manufacturer would reckon it is great.
Add all these error up and 6 degrees is pretty good.
An accurate compass is most important when manually steering or using a vane steering to it offshore. If you can steer within 10 degrees over time you are doing well.
Your compass is fine.

Rob S
VIC, 391 posts
23 Nov 2017 3:51PM
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Phill;

Step one in my procedure is exactly what you said. " 'learn' from doing a slow circle'. It works flawlessly. I have done this twice in three years. At installation and after one firmware upgrade. I am very happy that the chart plotter and multifunction display provide very accurate direction displays from the electronic compass.

I agree. Pressing AUTO maintains current heading and where you end up will be influenced by Leeway. I use AUTO a bit over short distances but on a long cruise I usually prepare a ROUTE file and tell the autopilot to follow the route and so it makes all the adjustments automatically for Leeway. Also, automatic Leeway adjustment occurs if using GO TO WAYPOINT . Anyway back to my topic.

Phill and Morning Bird

I don't do a lot of (any!) manual helming over long distances and being relatively new to sailing was not aware of the extent of 'normal' error in compasses and helming. Thanks for that. I assumed I would get all support systems (electronics, compasses and deviation charts) accurate to at least one degree. Then if I had to resort to manual helming I would do the best I could and correct heading based on position each hour from my backup portable GPS.

Morning Bird

I think you are meaning 'very local variation' Hydro office says the variation is 12.9 degrees East but you are saying something like a bit of wreckage in my path or maybe an iron deposit under the lake. I didn't think about that. Should try somewhere different.

And I didn't think about motor torque effects either but suspect it's not an issue with the two 9.9 hp high thrust Yamaha outboards at slow speed.

Thank you both for your input. I am going back to Paynesville next week. Think I'll try a few new ideas but accept perhaps it's as good as I get.

Rob

MorningBird
NSW, 2643 posts
23 Nov 2017 4:55PM
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Rob S said..

Morning Bird

I think you are meaning 'very local variation' Hydro office says the variation is 12.9 degrees East but you are saying something like a bit of wreckage in my path or maybe an iron deposit under the lake. I didn't think about that. Should try somewhere different.

And I didn't think about motor torque effects either but suspect it's not an issue with the two 9.9 hp high thrust Yamaha outboards at slow speed.




Yep, as you note there can be different variations on the earths magnetic field. A submarine cable is another.
You also might not have taken into account compass Deviation, the inherent error in the compass due to manufacture or siting on the vessel. Your compass card might be a degree or two misaligned in manufacture, it may be mounted on a bulkhead a s****teenth out causing the needle to be slightly off position, the compass may be affected by metal in the boat. This latter affect on the compass might vary depending on the boats heading.
All these little errors add up, 6 degrees is pretty good.
I am way out of date on the subject, there are people who specialise in yacht compass swings who might be able to help further.

Kankama
NSW, 603 posts
23 Nov 2017 6:03PM
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I don't even look at my compass. Hell I haven't had one on the binnacle for years (I do have one a combination handheld with light that can mount there when needed - but it hasn't been needed.) The GPS is all I want nowadays. That gives me the track. Then I adjust the autopilot left or right depending on where we are on the chart. Sometimes I do not want to keep down the centre of the track.

For instance, when coming south from Mackay to Curlew I let the boat get pulled to leeward with the incoming tide. The boats with the GPS tied to the autopilot fought to stay down the rhumb line. Then the tide turned and we got pushed back to the rhumb line when all the boats that had stayed on track had to sail deep. We just sailed at the best wind angle, beat em by hours.

Sailing boats don't go straight. Mine doesn't. So I work out where I am, what the wind will let me do to sail the best VMG and then work out gybing or tacking angles later. I rarely sail down the straight line on the chart, but I do have a cat that likes it when I sail good angles.

So, don't worry about getting the compasses super accurate unless the GPS goes down. Then a compass within 10 degrees will do fine as long as you don't trust it too much and check against other nav aids.

MorningBird
NSW, 2643 posts
23 Nov 2017 6:17PM
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Kankama said..
I don't even look at my compass. Hell I haven't had one on the binnacle for years (I do have one a combination handheld with light that can mount there when needed - but it hasn't been needed.) The GPS is all I want nowadays. That gives me the track. Then I adjust the autopilot left or right depending on where we are on the chart. Sometimes I do not want to keep down the centre of the track.

For instance, when coming south from Mackay to Curlew I let the boat get pulled to leeward with the incoming tide. The boats with the GPS tied to the autopilot fought to stay down the rhumb line. Then the tide turned and we got pushed back to the rhumb line when all the boats that had stayed on track had to sail deep. We just sailed at the best wind angle, beat em by hours.

Sailing boats don't go straight. Mine doesn't. So I work out where I am, what the wind will let me do to sail the best VMG and then work out gybing or tacking angles later. I rarely sail down the straight line on the chart, but I do have a cat that likes it when I sail good angles.

So, don't worry about getting the compasses super accurate unless the GPS goes down. Then a compass within 10 degrees will do fine as long as you don't trust it too much and check against other nav aids.


Many sailors rely on chartplotters/GPS. So do I in the right situations. However, it can get even experienced sailors in real danger.
Probably worth doing the Yachtmaster Offshore theory course. It addresses the shortcomings of this approach so at least the risks are known.

Kankama
NSW, 603 posts
23 Nov 2017 7:45PM
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Actually I don't use a chartplotter - just the old GPS 128 and a computer plus, and this a big plus a big paper chart.

The paper chart is not really for navigation per se, more for getting a good grip on the trip in my head. I can pore over it before we go and get to know the hazards, plot them out, get my safety zones set, look out for shoals, like the John Young banks off Jervis Bay. I leave it out on the bridgedeck table and have the gps going too. You get a great sense of where you are on the chart.

There have been quite a few people who have missed a hazard, and run into reefs, using plotters. I feel that I could do that too so still get the paper charts to get the "vibe". For plotting distances and courses I tend to use OpenCPN as this is a bit easier. Still I like to keep my hand in. in case the batteries fail.

I had a friend who told me about learning running fixes and cocked hats et al on his yachmaster course. He is only 10 years younger than me and that is enough for him to always have had GPS on his boats. I did a few trips the old way first. But I love my GPS nowadays, just knowing where I am is fabulous and I still remember wishing I could work out my position to within a few miles in the dark years ago. GPS - ooh ahh, we used to dream about GPS - luxury.

cheers

Phil

NowandZen
WA, 382 posts
23 Nov 2017 9:17PM
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I tried swinging my mag compass without success - it resembled something like Jonny Depps in Pirates Of The Carribbean.
I ended up calling a professional to do it, Andrew Laslett, he is SA based, but I think he does jobs in Victoria also.
Did a great job that took a fair while to get it calibrated, but I was very happy with the outcome when he finished. He had to account for electrical field interference on my helm position. I never realised how difficult a job it was.
Here's his link:

www.compassadjuster.com.au/Adelaide.htm

I hope this helps.

Rob S
VIC, 391 posts
24 Nov 2017 4:59PM
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NowandZen said..
I tried swinging my mag compass without success - it resembled something like Jonny Depps in Pirates Of The Carribbean.
I ended up calling a professional to do it, Andrew Laslett, he is SA based, but I think he does jobs in Victoria also.
Did a great job that took a fair while to get it calibrated, but I was very happy with the outcome when he finished. He had to account for electrical field interference on my helm position. I never realised how difficult a job it was.
Here's his link:

www.compassadjuster.com.au/Adelaide.htm

I hope this helps.


Yes, I am considering this if the result of my next attempt is still illogical.
We have a Victorian licenced adjuster on the same web site who schedules visits to the Gippsland lakes.

dialdan
QLD, 79 posts
24 Nov 2017 4:29PM
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Kankama said..
Actually I don't use a chartplotter - just the old GPS 128 and a computer plus, and this a big plus a big paper chart.

The paper chart is not really for navigation per se, more for getting a good grip on the trip in my head. I can pore over it before we go and get to know the hazards, plot them out, get my safety zones set, look out for shoals, like the John Young banks off Jervis Bay. I leave it out on the bridgedeck table and have the gps going too. You get a great sense of where you are on the chart.

There have been quite a few people who have missed a hazard, and run into reefs, using plotters. I feel that I could do that too so still get the paper charts to get the "vibe". For plotting distances and courses I tend to use OpenCPN as this is a bit easier. Still I like to keep my hand in. in case the batteries fail.

I had a friend who told me about learning running fixes and cocked hats et al on his yachmaster course. He is only 10 years younger than me and that is enough for him to always have had GPS on his boats. I did a few trips the old way first. But I love my GPS nowadays, just knowing where I am is fabulous and I still remember wishing I could work out my position to within a few miles in the dark years ago. GPS - ooh ahh, we used to dream about GPS - luxury.

cheers

Phil


Love to know where you get the charts for Open CPN
Al

MorningBird
NSW, 2643 posts
24 Nov 2017 6:12PM
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Select to expand quote
Kankama said..
Actually I don't use a chartplotter - just the old GPS 128 and a computer plus, and this a big plus a big paper chart.

The paper chart is not really for navigation per se, more for getting a good grip on the trip in my head. I can pore over it before we go and get to know the hazards, plot them out, get my safety zones set, look out for shoals, like the John Young banks off Jervis Bay. I leave it out on the bridgedeck table and have the gps going too. You get a great sense of where you are on the chart.

There have been quite a few people who have missed a hazard, and run into reefs, using plotters. I feel that I could do that too so still get the paper charts to get the "vibe". For plotting distances and courses I tend to use OpenCPN as this is a bit easier. Still I like to keep my hand in. in case the batteries fail.

I had a friend who told me about learning running fixes and cocked hats et al on his yachmaster course. He is only 10 years younger than me and that is enough for him to always have had GPS on his boats. I did a few trips the old way first. But I love my GPS nowadays, just knowing where I am is fabulous and I still remember wishing I could work out my position to within a few miles in the dark years ago. GPS - ooh ahh, we used to dream about GPS - luxury.

cheers

Phil


Don't get me wrong, I use GPS and chartplotter all the time, with fixes on a paper chart every hour coastal and once a watch offshore.
The danger I was referring to is using a "steer to waypoint" and allowing the tides/currents to take you away from the track and then back again.
In effect when doing this, relying only on the GPS, you don't know where you are in relation to the hazards at any particular time. This might not be a problem most of the time but when it becomes a habit and you do it going through Torres Strait, or the English Channel, or similar you could end up on the putty.

Kankama
NSW, 603 posts
25 Nov 2017 8:50AM
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Yeah, I get the idea of danger zones and letting yourself drift onto reefs. On the trip to Curlew I plotted my course and kept a lookout. As I said before, my boat doesn't always like going straight so I sometimes have trips where I have to up the navigation skills. For instance, in lightish winds an alteration of only 15 degrees can almost double the boat speed under reacher by generating more apparent. When the wind comes up I often go straighter but sometimes veer around for comfort. I wouldn't do it where there are nasty shoals - but the vast majority of the coast is clear.

Still, you have to be careful to know what is around. I think paper charts let me get this situational awareness better than the computer. Otherwise this could happen

www.yachtingworld.com/blogs/elaine-bunting/comment-how-the-team-vestas-wind-crash-really-happened-and-the-surprisingly-simple-things-we-can-learn-from-it-62634

As for OpenCPN charts - mine are not all that good. Some have some errors which is a worry. I am using Navionics too, on my next trip in a week.

cheers

Phil

Ramona
NSW, 7388 posts
25 Nov 2017 5:16PM
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Love to know where you get the charts for Open CPN
Al


Al,
This depends where you live. If you are in the USA you can download NOAA charts for free. If you are in New Zealand you can download charts for free. If you are in NSW you can download the charts in PDF form from Waterways for free. These are very accurate charts but come with annoying safety messages. Otherwise you can buy charts from the usual suspects. The other way is to have friends that will swap files.



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"Help Please with Compass Adjustment" started by Rob S