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Old 19 August 2006, 07:25   #1
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Compass fitting.

I've got a top mounted Ritchie compass here waiting to be fitted.I'm not sure how far it needs to be from the VHF-there isn't anywhere more than 30cm away from it that is feasable to fit it.

Suggestions please?
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Old 19 August 2006, 09:15   #2
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Nos I use to be a flyer before a ribster, the compasses are calibrated to the individual plane via the 2 way adjustments which should be present on your compass, but you do need a second compass mounted away from any metallic object to calibrate from.

The easier option is switch all electrics on and hold the compass a couple of foot away from the vhf, as you move the compass closer you will see the deviation, place this just outside deviation range, but i suspect you will still be able to mount this reasonably close to the radio.

its about time i had some useful advise for you, its normally the other way around
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Old 19 August 2006, 09:29   #3
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Cheers Ian!

It's only a baby compass though-one of these.



Would the adjustment be internal or would it even have any?
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Old 19 August 2006, 10:06   #4
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Normally 2 obvious screws or poss to holes with posi adjusment for magnetic deviation.

perhaps it does not have it!! the vhf may pull it 15-20 degrees off depending on location to VHF. but blasting along at 20knts the compass normally moves about that back and forth anyway..
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Old 19 August 2006, 10:35   #5
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Interesting - maybe this explains why the compass fitted to my boat is only slightly less useless than the speedometer

Does the VHF have an effect only when transmitting, or all the time (due to magnet in the speaker or whatever?)

IIRC radiation decreases as the cube of distance or something - there was a big discussion about it here recently when the first mobile phone masts were installed and one was next to a kiddies playground and all the mummies were up in arms about their children being microwaved
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Old 19 August 2006, 10:45   #6
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My compass is surrounded by electronic things, see pic, and I was initially concerned about it. However, the compass is not deflected when any or all of the electronics are switched on. I suppose it might when I transmit on the VHF, but I hardly ever do that.

There's a little book I've found useful in the past called 'Compasses in small craft', by Cmndr C. A. Lund, ISBN 0 85174 237 8. I still need to use it to sort my compass, though it seems about right on most courses.

Cheers Tony
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Old 19 August 2006, 11:13   #7
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aha! It DOES have adjustment! I thought the screw holes I could see were for dismantling the casing but then realised the casing clips together.You can see one of them on the picture.

Ok...

How do I adjust it? What screw does what?

There's the one in the pic and one 90 degrees anticlockwise to it on the casing.
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Old 19 August 2006, 13:35   #8
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Hi Nos
never had any need to adjust the compasses on our ribs. Vhf is a foot or so away and the mic is nearer but now they dont have a magnet and cone thing in them they dont seem to affect compass. I always plug new kit in, turn it on and wave it around the compass before fitting to see if there is any efect.
adjusting-just found instructions for last compass with the following advice- none of which we had to use!

Use chart to determine a north heading and steer boat on it of N doesnt line up use compensation rod on right hand side to adjust til N is right.
Now head to an east heading and if compensation is req then adjust using rod in front of compss until E lines up
Head South and if heading is not correctly shown adjust the side comp rod to take out half the error
Head west and use front comp rod to take out half of any error

Repeat the steps as above taking out half the error at each adjustment until req accuracy is achieved.
If you cant get it right you may need to move something or indeed the compass itself.
Use a non ferrous/non magnetic screwdiver to do the adjustments.

Steven your compass should work-consider if it is a compass weighted for the N Hemisphere. Cos the pull from the poles is downwards, as well as up as it were, the indicator of a compass may be weighted to compensate for the downward pull which will be on the other side where you are on the underneath bit of the world .
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Old 19 August 2006, 13:42   #9
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I fitted mine right below my VHF and other gadgets. I took some time and trouble when first looking at fitting mine but found that none of the instruments seem to affect its accuracy. When I fitted a new steering wheel (supposedly Stainless Steel) when I rotated it my compass deviated by at least +/- 35 deg. Luck had it I had a De-Magnetizer at work. Anyway I don't think too many a skipper of RIB can reliably use their compass to any degree of accuracy anyway (not like a Yachtee), Being no more of a North, East, South, and West direction indicator so I recon that a +/- 15 deg accuracy is OK on a RIB.

What do other people think?
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Old 19 August 2006, 14:23   #10
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Quote:
Originally Posted by wavelength
Steven your compass should work-consider if it is a compass weighted for the N Hemisphere. Cos the pull from the poles is downwards, as well as up as it were, the indicator of a compass may be weighted to compensate for the downward pull which will be on the other side where you are on the underneath bit of the world .
So what you are saying Dave is that it will work when my boat is upside down?

It works, it just doesn't seem very accurate/consistent compared to the GPS heading, haven't really checked but probably out by 15-20 deg?

I don't think I will get lost anyway, offshore navigation is not on my list of goals to achieve, heading due east from Port William the next stop is Chile 13,000 miles away, and going the other way all we've got is the Argies and even that is about 300 miles, so I think I'll stay in sight of land for now
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