Electronic Instument near compass?

Fascadale

Fascadale

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I'm thinking of mounting an instument near my compass. Is this likely to create any deviation.

The compass is a Plastimo Contest type bulkhead mounted and the instument maybe Nasa Log/Depth.

The instrument may be mounted within 3 inches of the compass
 
While waiting for jokaboat to compile his more expert assesment take a look at the Nasa website and the instruction manual for the instrument to see if there is any "compass safe distance" in the description or specification. If not contact Nasa.
 
It's perhaps a bit optimistic to expect to find anything much in the Nasa manuals! However, other makes often suggest a compass safe distance. Raymarine usually suggest about 230mm minimum, so putting it 3" from the compass could be a problem.
 
Big ships compasses require 6 foot (or modern metric equivalent) small boat as far as possible.

Could try the "suck it and see course" try the fit and see how much error you get, and prepare the deviation curve.

Having said that, in smaller boats steering within five degrees of the course seems to be a rarity so I wouldn't worry too much /forums/images/graemlins/smile.gif
 
the magnetic field generated by a DC appliance is proportional to the current taken which for an instrument is pretty small. No speaker with magnets inside so my guess would be that it would not be a problem. Only way to be sure is to try it.

I have an autohelm control inc electronic compass about 4 inches above my steering compass and I cant find any effect.

Make sure any 12v wire feeding the instrument is twisted.
 
Only way is to fire it up, then move a compass around it, you need to cover all headings, and don't forget to try it with the backlight on.
 
[ QUOTE ]
Make sure any 12v wire feeding the instrument is twisted.

[/ QUOTE ] Dont start that debate again!
 
[ QUOTE ]
what is this about twisting the wires

[/ QUOTE ] Usually crops up when talking about the wiring for a compass light.

The usual advice is that the wires to the light should be twisted together to minimise the effect of the magnetic field around them.

Each wire has a field that runs round the wire (You must remember that from your schooldays ... I do!) that can affect the compass but in opposite directions around the positive and negative wires. With a bit of twin flex the two fields more or less cancel each other out. If the wires are twisted then it helps to maximise the self cancelling effect.

Some will say that the twisting makes or no little extra difference.

One day I am going to check it all out with a proper scientifically controlled experiment.
 
Every piece of marine electrical and electronic equipment should have what is called a "Compass Safe Distance" either marked on the product or given in the manual. No ifs or buts.
 
[ QUOTE ]
No ifs or buts.

[/ QUOTE ] "but" "if" its a Nasa it doesn't, at least not in the manual. I checked after suggesting it.
 
Thanks for the advice on the twisting,

School days, a very long time ago but now that you mention magnetic fields I begin to remember.

"Compass safe distance", I'll check this out

Thanks again
 
Compass safe distance applies behind bulkheads as well !! Been on many boats where the fact compass is out of sight (other side of bulkhead) gear is fitted. Point out to owner and the look of dawns light on the face !

Most digital display gear has little effect on compass and as another says - test is to move the gear around the compass while its working, and with backlight on as well.

Despite cries of Hell and damnation ... my Plastimo Contest has 2 items mounted behind the bulkhead about 10" from the back of bowl. VHF and Car audio. Being easily de-mountable in a 'hanging box' I decided to fit and then gauge the effect.

First compass readings taken before fitting. Second handheld compass passed all round the box and gear to see if deviation caused. Third fit box and gear and read compass again. Switch on gear and play with it transmitting, turning up volume etc. etc. reading compass again.
Result ? Box and gear remain mounted and naff all deviation / change to compass readings.

I like many others have a small boat (I have 4 actually but that's another story) ... and that means distance that can be afforded to things like compass etc. is restricted. Compromise of minimum deviation and location has to be made.
The point of steering a course is valid and let's be honest the compass is an indication of general direction rather than exact by nature that most of us can't steer to single degrees ! Handheld compass is the one that really needs accuracy as it's the one used for taking the bearings unless you use pelorus. Course made good on chart is the decider and you amend steering order accordingly..... + / - number of degrees necessary.
 
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