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Old 02-06-2011, 22:13   #1
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Mounting Fluxgate Compass in Aluminium Yacht

Hi, I am about to mount a fluxgate compass into my aluminium yacht, do I have to treat it like a steel yacht and mount it outside or can I treat it likea grp yacht and mount it inside?
Does the aluminium act as a magnetic shield, doesn't appear to effect the hand held compass inside the yacht?
Thanks for your advice?
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Old 02-06-2011, 22:22   #2
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Re: mounting fluxgate compass in aluminium yacht

Aluminum is the same as FRP as far as earth's magnetic field is concerned: no effect on compass sensing.
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Old 02-06-2011, 22:44   #3
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Re: mounting fluxgate compass in aluminium yacht

Thanks Daddle, very helpful, as always!
Cheers from Keith.
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Old 02-06-2011, 23:24   #4
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Re: mounting fluxgate compass in aluminium yacht

Just be sure to use bronze or nonferrous screws to mount it.
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Old 02-06-2011, 23:30   #5
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Re: mounting fluxgate compass in aluminium yacht

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Just be sure to use bronze or nonferrous screws to mount it.
Aaaack! Never put a bronze, brass or copper part onboard an aluminum boat. That's what I heard...it might fall somewhere and corrode a hole. Better to use a stainless screw that has been checked with a magnet, or checked near a compass, that it hasn't somehow ended up with some ferromagnetism.

The aluminum boat I was on didn't even allow pennies to come aboard in purses or pockets.
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Old 02-06-2011, 23:43   #6
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Re: mounting fluxgate compass in aluminium yacht

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Aaaack! Never put a bronze, brass or copper part onboard an aluminum boat. That's what I heard...it might fall somewhere and corrode a hole. Better to use a stainless screw that has been checked with a magnet, or checked near a compass, that it hasn't somehow ended up with some ferromagnetism.
Just use some Tef-gel on the treads. TEF-GEL - Ultra safety systems - Home page
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Old 03-06-2011, 11:46   #7
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Re: Mounting Fluxgate Compass in Aluminium Yacht

Some aluminum alloys react very badly to the presence of any copper. Supposedly if you put a penny (then copper) in the bilge of an aluminum boat fifty years ago, it would "burn" a hole through the hull in just a few months. While different alloys have supposedly reduced that problem to near-nil...I think I'd rather see a (wood, etc.) block glued to the hull, and any screws inserted into that block, so there's no metal-to metal contact possible, no problem possible. TefGel or not.
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Old 03-06-2011, 14:24   #8
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Re: mounting fluxgate compass in aluminium yacht

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Originally Posted by daddle View Post
Aaaack! Never put a bronze, brass or copper part onboard an aluminum boat. That's what I heard...it might fall somewhere and corrode a hole. Better to use a stainless screw that has been checked with a magnet, or checked near a compass, that it hasn't somehow ended up with some ferromagnetism.

The aluminum boat I was on didn't even allow pennies to come aboard in purses or pockets.
I am straying a bit here, but never use bilge pump switches containing Mercury in an Aluminum boat.
The liquid eats right thru Aluminum very quickly.
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Old 03-06-2011, 19:51   #9
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Re: Mounting Fluxgate Compass in Aluminium Yacht

Wow................ Thanks heaps guys!
Compass is mounted below aft bunk and ok!
Did find a copper/brass penny in the motor bilge when cleaning it out, sitting in salt water, but had not corroded at all and was not shiny, no holes in the bilge yet???
Plus about 10 screws/pop rivets/washers etc washing around???

Have got 1 milliamp voltage from the positive battery terminal to the hull, but no direct connection whatsoever, enough to light up a very small led, but it lights up if I hold one end and touch the hull as well?

Did have 150 milliamps on the hull until I removed the leaking salt water pressure pump, now have hand salt water pumps and a double pole switch on the fresh water pressure pump.

I thought alloy boats were maintenance free???? Ha! ha!

Off to Chenang beach today from Rebak, then Penang Tuesday for visa and the Sumatra over the weekend!
You Beauty!!!! Cheers from Keith.............
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Old 03-06-2011, 21:23   #10
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Re: Mounting Fluxgate Compass in Aluminium Yacht

Kanter even nickle plate bronze through hulls. I repeat what others have said, never use bronze on an aluminum boat.
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Old 04-06-2011, 00:18   #11
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Re: Mounting Fluxgate Compass in Aluminium Yacht

It's an old wives tale that copper will burn a hole through aluminum. I have had an aluminum hull boat for over twenty years and have pulled bronze screws out of the bilge...no damage. Modern pennies are mostly zinc by the way.

I mounted my fluxgate using stainless steel screws. Mount it as far way from the engine and 12 volt DC wires as you can. Some fluxgates allow you to run a circle with the boat which creates an electronic deviation table which compensates for the iron onboard.

I used to have bronze thruhulls when the boat was inspected because the USCG did not allow plastic thruhulls. I used isolators to stop any corrosion which worked fine.

With an aluminum hull you want what is called a floating DC system. Absolutely none of your 12 VDC system should electronically attach to the hull. None of your AC system as well except for things like the frame of your inverter.

You can have bronze touching the aluminum on an aluminum hull....just not where it gets wet. I have this all over the inside of my cabin where bronze screws and bolts attach the interior trim to the hull and bulkheads. No corrosion for a boat built in 1975.
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Old 04-06-2011, 00:42   #12
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Re: Mounting Fluxgate Compass in Aluminium Yacht

I had an alloy yacht which had jacklines attached to U-bolts on the deck. The wires had copper swages which lay on the alloy and ate through 3mm deep over period of three months or so. Have had copper wiring pieces fall into the bilge and do the same thing where the paint had lifted away. All for keeping copper out of alloy boats and being very careful/clean when working on the electrics. Have not tried coins with copper content.
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Old 04-06-2011, 00:59   #13
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Re: Mounting Fluxgate Compass in Aluminium Yacht

That's exactly it. Where it is wet or might get wet, you do not want copper touching aluminum. Where it is dry there is no problem.
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Old 04-06-2011, 04:13   #14
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Re: Mounting Fluxgate Compass in Aluminium Yacht

We have several fluxgate compass inside Azawakh (aluminium) and they all work fine since years.
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Old 04-06-2011, 08:05   #15
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Re: Mounting Fluxgate Compass in Aluminium Yacht

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That's exactly it. Where it is wet or might get wet, you do not want copper touching aluminum. Where it is dry there is no problem.
Correct. For electrolysis to occur you need all three:

1. Anode
2. Cathode
3. Electrolyte (= water in this case)

which means that copper & aluminium in a dry environment is not a problem.

ciao!
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