Aligning Fluxgate Compass

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   I have replaced the erractic and now dead Simrad wheelpilot on my 315 with a Raymarine SPX-5 wheelpilot, and now have 3 compass readings - the boat compass, the chartplotter, and the fluxgate display.  The Simrad WP of course had a fluxgate compass, but no display.  The boat compass and the GPS have always been about 10 degrees different.

So my question now is which compass to align the Raymarine fluxgate with?  If I align it with the boat compass, at least I'm looking at compatible information.  But if I want the wheelpilot to steer to a waypoint, the GPS is telling it where to go and if it's not aligned with the GPS, it won't know exactly where to steer.  Or is there some self-correction software at work?

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tony1 Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Joined: 18 October 2005 Location: Brockenhurst Status: Offline Points: 29	Post Options Post Reply Quote tony1 Report Post Thanks(0) Quote Reply Topic: Aligning Fluxgate Compass Posted: 24 March 2012 at 10:49
	I have replaced the erractic and now dead Simrad wheelpilot on my 315 with a Raymarine SPX-5 wheelpilot, and now have 3 compass readings - the boat compass, the chartplotter, and the fluxgate display. The Simrad WP of course had a fluxgate compass, but no display. The boat compass and the GPS have always been about 10 degrees different. So my question now is which compass to align the Raymarine fluxgate with? If I align it with the boat compass, at least I'm looking at compatible information. But if I want the wheelpilot to steer to a waypoint, the GPS is telling it where to go and if it's not aligned with the GPS, it won't know exactly where to steer. Or is there some self-correction software at work?

panos Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 02 March 2008 Status: Offline Points: 1939	Post Options Post Reply Quote panos Report Post Thanks(0) Quote Reply Posted: 24 March 2012 at 13:28
	Hi, There is a difference between magnetic North pole and the geographic Earths North pole. The magnetic compass aligns itself to the earths magnetic field and always shows to the magnetic north pole (of course needs calibration to compensate the disturbance by heavy metal objects. Mainly the engine) The fluxgate compass reads also the magnetic field. By turning the boat at a constant speed it calibrates itself, but has no way to know where is the Magnetic North direction. You need to enter the Magnetic North direction - align it to the boats compass! The GPS does not work by the magnetic field. It reads the distances from satellites orbiting the earth and calculates the position by trigonometric calculations. The direction it shows is the geometric - TRUE NORTH . In some lucky places -like Europe for example- the difference between True North and Magnetic North is just a few degrees and can usually be ignored for short passages. The above is not true everywhere! There are some places on earth where the magnetic field is so disturbed that the magnetic North direction shows to the Earths South Pole! Extreme care is needed to navigate in these places. Check to find the local magnetic declination before calibrating the compasses. For your safety you need to be able to navigate without the help of the GPS, just in case! http://upload.wikimedia.org/wikipedia/commons/d/d4/World_Magnetic_Declination_2010.pdf Edited by panos - 24 March 2012 at 13:37
	Panos Hanse 630e - selling her -

echoofwight Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 08 August 2007 Location: Portsmouth UK Status: Offline Points: 270	Post Options Post Reply Quote echoofwight Report Post Thanks(0) Quote Reply Posted: 28 March 2012 at 13:59
	Hi Tony, where do you sail, if like me you are on the UK south coast the difference is about three degrees. I aligned my SPX-5 by using the GPS reading but you need to be in slack water and traveling faster than about three knots. GPS shows the boats direction of travel. Ships compass shows the way the boat is pointing. These are often different especially in tidal streams.
	Steve. Hanse 341 Echo of Wight, . Deep draft and rudder, white hull, Single aft cabin. Raymarine instruments. Raymarine radar. Garmin AIS. Wheel Steering, Portsmouth.

tony1 Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Joined: 18 October 2005 Location: Brockenhurst Status: Offline Points: 29	Post Options Post Reply Quote tony1 Report Post Thanks(0) Quote Reply Posted: 28 March 2012 at 18:07
	Hi Steve - I sail from Buckler's Hard. Where did you instal your fluxgate compass? Mine is (so far) in the front cabin - as far away as I can get it from loudspeakers etc. I thought I had it aligned to the boat compass, but discovered yesterday that it is accurate on port tack, and about 40 degrees out on starboard tack! Perhaps alignment to GPS would be better - I take your point about cross-track error.

echoofwight Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 08 August 2007 Location: Portsmouth UK Status: Offline Points: 270	Post Options Post Reply Quote echoofwight Report Post Thanks(0) Quote Reply Posted: 30 March 2012 at 08:28
	Hi Tony, I sail out of Portsmouth Harbour. I like Bucklers Hard it must be a great place to sail from. My fluxgate compass is below the bunk in the forcabin. So far this has worked great. Overall I have found the SPX-5 an improvement over the simrad WP20 that I did have. I have in fact changed all the instruments from Simrad to Raymarine. I don't understand the diference on port and starbord tack, is the fluxgate mounted facing for and aft and upright. Or is the ship compass diferent on for and aft. Steve
	Steve. Hanse 341 Echo of Wight, . Deep draft and rudder, white hull, Single aft cabin. Raymarine instruments. Raymarine radar. Garmin AIS. Wheel Steering, Portsmouth.

Goodie Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Joined: 09 November 2006 Location: Canada Status: Offline Points: 48	Post Options Post Reply Quote Goodie Report Post Thanks(0) Quote Reply Posted: 17 May 2013 at 01:57
	Can someone advise me on where I can expect to find the fluxgate compass (I think it is the RC36 model) on my 2007 Hanse 370. It was installed by Hanse at their factory when they installed my Simrad AP 25 auto pilot at the time they built the boat. I have traced the wire for the fluxgate compass from the AP 25 auto pilot in the cockpit along the port side to the bulkhead separating the forward cabin from the main salon. Presumably it should be centred (or near the centre line of the boat) and I would assume somewhere low in the forward cabin, perhaps below the birth? My thanks. Goodie Karinya Hanse 370 #251
	Goodie 370 #251



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