Compass deviation on steel boats

[mireland]

I know this is tricky already and I am not surprised that the compass is way off. However I wonder why the fluxgate in the ST 3000 autohelm is also way off and by the same amount as the main compass?

1. Can the compass in the ST be easily adjusted?
2. What is the easiest way to adjust the main compass. I have no tender incidently and all compasses used on board are mad including the handheld!? All the methods so far seen seem hideously complex and quite beyond me.



<hr width=100% size=1>

 

[snowleopard]

does your autopilot not have a deviation calculation built in. with my st5000+ i just had to motor slowly round in circles and it worked it all out for itself. in my case it said it was no more than 1 deg. so can't tell how it compares to a manual swing.

<hr width=100% size=1>

 

[BigART]

This might be a bit late for you, but our steel vessel has the transducer mounted half way up the mast and works well. The main compass has been well adjusted and has a maximum deviation of 3°. I wonder if there are degaussing facilities available. Has she been struck by lightning?

<hr width=100% size=1>

 

[mireland]

Thanks for replies. Does anyone know of a compass adjuster in the Bristol area?

<hr width=100% size=1>

 

[William_H]

You might find it worthwhile to roam around the boat with the handheld compass and you might just find some dramatic source of magnetism. From theory and a wild idea but..... You would need to remove all equipment that has a permanent magnet, small motors compass radio speakers. Actually you should do this anyway and check for compass errors without the equipment. You then need a whole lot of insulated wire to wrap several turns around the hull in a horizontal plane like lifelines and repaeat later with wires around the girth ie from deck under water up the other side. You will need to find a transformer giving low voltage high current AC to connect to the coils. You will need a light dimmer so that power to the transformer can be reduced to zero slowly. (over 1 or 2 seconds) The theory is that the coil magnetises the boat first in one direction then the other at 50 hz this is slowly reduced until the residual magnetism is near zero. Now it will work in theory however... can you get enough magnetic flux from at most practical 10 turns of wire and can you get enough current into the coil and will your light dimmer go all smokey? I write this perhaps for amusement or to give you some ideas. I think a professional degauser will do the same thing. When degausing aircraft engine crankshafts after magnetic particle crack testing a coil with AC is used however the field is reduced by removing the shaft slowly from the coil. Not so easy with a ship. regards will


<hr width=100% size=1>

 

[pampas]

A crude method of de-gausing is to wrap an ac. welding cable (About 2/3 turns) around the water line, remove all magetic sources especially the compass. Do a bit of welding on scrap steel (Do not connect the earth to the vessel and do the welding of the boat). Walk around with hand compass and compare with the original readings. I have degaused bildge keels with this method.
If ashore, do it about two days before lifting in, otherwise it will quickly take up the nearest N/S orientation, and then you are back to the start again.

<hr width=100% size=1>

 

[jeanne]

Try Andrew at WH Price, the chart agent on Wapping Wharf. He should be able to point you to someone who can adjust/advise on your compass.

<hr width=100% size=1>

 

[JEG]

Users on the metal boat society forum state that they have obtained excellent results when locating the sensor below decks. If I live long enough I plan to give it a try.

<hr width=100% size=1>

 

[AndrewB]

Below decks placement.

I saw that too, and find it very hard to believe. My solid-state handbearing compass gives complete nonsense inside my steel yacht, so why would a fluxgate compass work?

<hr width=100% size=1>