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Old 11 January 2007, 12:25   #1
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magnetic compass problem

hi all
I have a ribcraft which i thought had a faulty plastimo 105 compass but after fitting a new one found the siting of the compass the problem or more to the point the equipment around it.
The console is a large chart table one with the usual stainless grab bars,garmin plotter vhf and dials which as far as i can work out do nothing to the compass.
However fitted to the console is a stereo system (minus the front unit of the stereo ) with four speakers ,two on the back edge of the console and one either side These are not wired up at present but after moving the compass around the speakers i'm 90% sure its these causing a huge magnetic field.
I reckon if i could tip the boat in iron filings she'd look like a hedgehog..!!

So is there anything i can shield the compass with?
The nearest speaker is about 50-60cm below it but i wonder whether by sheer fluke they're aranged in such a way to cause a magnetic field.
The compass points west ("go west young man" ) all the time.
I've tried the compensators in the compass and they are not enough.
I have a bracket now so will try mounting it up a bit but it seems odd that the compass is fine until i place it within the confines of the console.
The only other thing i thought it may be is the compass is quite close to the hydraulic steering helm and next to that is the ignition key and kill cord switch.

Also the compass is right next to the filler/breather on the side . ie the filler goes through the console just under the compass.

Is there anything i can shield the compass in?
do plastimo do a binnacle for the 105?
If i wire up the speakers will this loose some magnetism?

Things i'm going to try is:

: to take out a speaker at a time and see what happens?

:Put the compass on the bracket (but i'll have to fill the hole it was in)

Anyone got any thoughts and had experience of stereo speakers and compasses?

Worst case for me is having to fill four 8" holes in the side of the console

Or paying for a professional compass adjuster to come over and fix it.

help any advice welcome
pete









I've got a mini c compass as well and this does the same thing.
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Old 11 January 2007, 15:11   #2
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I would be 99% certain it is your speakers causing the problems. Most modern plotters vhfs etc are magnetically shielded and are safe around a compass.
I put a compass on a the top of a jockey console. The boat had twin engines (hondas) and so all the dials were cramed in the front of the narrow console. The compass actually touched the bag of the rev counters. At the time the engines were pretty old and the dials made the compass head south permenantly. Got a compas swinger in and he corrected it to within 4degrees on all headings by fitting small magnets to the console.
Last year I replaced the engines (Mercs) (again the compass touches the dials) and again the compass was all over the place due to the new rev counters. I removed the magnets which had been put on by the swinger and the compass worked fine.
Before christmas I had the swinger back to check another boat and asked him to do a quick check on this boat and he found it to be correct to 2 degrees which will do for me!
There is also a gps plotter mounted within a couple of inches of the compass and this seems to have no effect.
I should imagine a vhf may have some magnets in but nowhere near the size of the ones in your four speakers.
First thing i would do is leave the compass where it is and take out the speakers to see if its them and resite them if necessary perhaps in seat pods or somewhere.
I would say the siting of your correctly reading compass is more important than your sound system if you out in the nasty stuff!!
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Old 11 January 2007, 16:15   #3
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It's definatly the speakers. All Speakers have Fkn great magnets in the back Look here:- www.bullnet.co.uk/shops/test/images/DCP00824.jpg

Resite them as far away as poss. Remember also your VHF will have a magnet in the speaker and Microphone.

Hope this helps
Brian
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Old 11 January 2007, 17:16   #4
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remove the speakers

did you consider removing the speakers to see what happens?

rgds
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Old 11 January 2007, 17:24   #5
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Quote:
Originally Posted by behavin View Post
.......Things i'm going to try is:

: to take out a speaker at a time and see what happens?

Yes, I think he did
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Old 11 January 2007, 18:47   #6
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Can you not buy shielded speakers for your Radio? I'm pretty sure I've seen some for sale somewhere, they use shielded speakers in TV's and AV speakers.

I'll have a search later.
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Old 11 January 2007, 19:31   #7
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A lot of people think a product is safe because it says "magnetically shielded". What they never mention is electromagnetic shielding.
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Old 11 January 2007, 20:28   #8
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Yeh, but that's not a problem in most speakers. More of an RF electrical issue with the instruments and most manufacturers are pretty well sorted in that area. Check for wiring as well, the bulb in my compass had the two wires twisted together. This caused a deviation in the compass, untwisting them sorted it. The only other problem I had with my compass was after I installed and new seering wheel, an 8 spoke rubber rimmed "stainless steel" design. When I turned it, the compass went all over the place. I took the wheel off and demagged it at work. It's No longer a problem.
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Old 11 January 2007, 20:29   #9
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Don't rely on the compass. Deviation is another factor to consider. Every boat is different with regards this. Certainly because of the many different outside influences on a small fast boat I don't think you can get much out of a standard compass on a RIB. Best bet in this day and age is a GPS chartplotter backed up with the standard boat compass and a handheld compass. One of them will point you in the right direction. Certainly as with most things if you are having problems it can always be sorted when you chuck money at it. This will sort you problem but are you prepared to chuck money at it. If a compass reading is your major perogative on your boat might be best off to rip all your other electronics out. Electronics upset standard compasses. As I said maybe you should take a handheld compass and stand at the back of the boat/or front when you want to try and take a decent fix.
Personally I always try and remember where the coast is. Even better don't go out if visibilty is going to be bad.
Must admit I have RIBCRAFT and the compass is quite good. Not that I have had to use it but it doesn't wander all over the place and seems quite stable. I'm not too sure if I would be happy to do anysort of navigation with it though. I would probably make Christopher Columbus look good with my traditional navigation skills.
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Old 11 January 2007, 20:34   #10
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Well you only really need to know where North, East, South and West are. You'll hit land eventually .
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Old 11 January 2007, 20:36   #11
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Well you only really need to know where North, East, South and West are. You'll hit land eventually .
Sort of what I was trying to get at. And you probably don't need a compass for that.
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Old 12 January 2007, 02:20   #12
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Sort of what I was trying to get at. And you probably don't need a compass for that.
In heavy fog, or at night away from lights, a compass would be about the only non-electronic method of finding direction.

jky
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Old 12 January 2007, 02:44   #13
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Thanks for the responses:
Yes as i said and has been suggested i will take off the speakers one at a time starting with the one under the compass.
I'll let you know what happens.

As to navigating I do and always will use my compass as the first aid to nav' every time.
Over here in the Scillies i could head in any direction and hit land but there wouldn't be much boat left..!!
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Old 12 January 2007, 07:04   #14
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Check for wiring as well, the bulb in my compass had the two wires twisted together. This caused a deviation in the compass, untwisting them sorted it.
That's interesting. The idea of twisting the wires is to cancel out the magnetic field created around them when the current flows. It's standard practice. Could you see the compass move when you switched the light on and off and if so, did it stop moving when you untwisted the wires?

Tony
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Old 12 January 2007, 07:45   #15
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That's interesting. The idea of twisting the wires is to cancel out the magnetic field created around them when the current flows. It's standard practice. Could you see the compass move when you switched the light on and off and if so, did it stop moving when you untwisted the wires?

Tony
Yes, that's exactly what happened. I had to buy the bulb and holder seperatly (it's a plastimo one). I did read all the info when setting it all up, but can't remember if the instructions told me to twist or not (was 3 years ago).
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Old 12 January 2007, 07:57   #16
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I'm having the same problem at the moment, I fitted a plotter and planned to relocate the compass further back, in the centre on the console, but in the position I would like it to go it swings about 20 degrees out)

You can buy compasses that offer the facility to adjust or compensate for other offending objects or equipment. I'm not sure how compact/whether they make on that will suit your purpose/size/hole! but plastimo make some:

go to this link and click: Horizon 135 compass on the menu on the left:

http://www.plastimo.com/catalogue/in...tid=1&LangID=1
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Old 12 January 2007, 08:02   #17
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BTW alternatively and a cheaper option, buy some small magnets, work out where they need to go and how many you need to correct the problem and araldite them to the side of the compass until you compensate for the problem! - I've done this before and it works.
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Old 12 January 2007, 08:06   #18
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The other option to consider is using a fluxgate compass with a display.

You can then place the sensor in the best suitable position away from stray fields, (up to 5m away from display). Still won't be perfect but may help. All the usual suspects make them - NASA, Raymarine, Navman etc.

Bit more expensive that a regular compass and some people just don't like not having a 'real' compass. Does need power as well of course, but if that's failed, which way you're pointing is the least of your worries.
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Old 12 January 2007, 08:37   #19
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been here before to a certain extent
Compass fitting.
the mic for our icom had no speaker thingie in it at all but instead a carbon pellet which sensed the voice vibrations and had no effect on the compass. Compasses do work, bloody hell we went for miles on a compass and a watch before we had decca and later gps. Takes some forward planning and some experience in steering to it, but there was life at sea before gps, honest! All our advanced clients steer a long course home at night by compass with the gps switched off and I'm still here, so the compasses must work!
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Old 12 January 2007, 19:21   #20
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I always take out a handheld compas on a neckstrap, it works for me!

Whenever I switch on a GPS the first thing I see is a disclaimer from the manufacturer telling me that they don't take any responsibility for the accuracy of the information the GPS gives you.......call me old fashioned but that bothers me.

I am with Mikecc on this one and believe the only true solution to the compasss issue is to use a fluxgate
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