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Old 07-06-2011, 17:36   #31
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Quote:
Originally Posted by hellosailor
...has anyone ever seen proof of any ali mast ever experiencing eddy currents caused by anything that created any magnetic field for any time in that mast?
What are you writing about?
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Old 07-06-2011, 19:59   #32
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Re: Mounting Fluxgate Compass in Aluminium Yacht

Daddle, I was asking about aluminum masts. But apparently I got auto-corrected from "aluminum" to "ali".

I'm skeptical that an aluminum mast will ever have enough induced eddy currents from the earth's feeble magnetic field, to create an additional local magnetic effect on a fluxgate compass.
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Old 08-06-2011, 01:46   #33
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Raymarine ng pin and wires descriptions for joining them.

Do any of you guys know what the pins/wires on the raymarine...

3 wire sea talk cable...

5 wire ng spur to T piece connector cable, the white one that goes to instruments from the T pieces....

6 wire ng spur cable, 5m long ones, that connect the T pieces together od, the blue leads.

As I want to join ST60 INSTRUMENTS TO ST70( only seatalk ng connections) COURSE CONTROLLER, TO A50 CHART PLOTTER,(has seatalk ng connector and nmea in and out) TO a set of ST60 wind and speed/depth guages(only sea talk connections), and a st60 data repeater with only seatlk 3 pin connectors in and out), phew??

So, counting the middle pin as 1 and going clockwise we have 5 pins on saetalk ng connectors, 6 pins on the T piece ng spur cable connectors and 3 pins on the old sea talk connectors.

Which ones are power, + and -?,, which ones are data, which ones are nmea pins, or doesnt the sea talk bus carry nmea data??

I also have an X10 course computer in the system which has input for nmea in and out and seatalk and seatalk ng, but I am short on seatalk ng cables and connectors, can I join them up by soldering 5 wire cables between them? I want the wind and speed and log data to get to the course computer so it can be shared 1on the bus.

Any one have the pin info or a site that shows it please?
Cheers from Keith, in penang getting indo visa for 2 months.
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Old 08-06-2011, 02:27   #34
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Re: Mounting Fluxgate Compass in Aluminium Yacht

OOps, I see I cant delete the post about raymarine pin info now, sorry, I have started a different thread about this question. Blue spur cables should read as backbone cables, 6 pin.
Keith
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Old 09-06-2011, 03:07   #35
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Re: Mounting Fluxgate Compass in Aluminium Yacht

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Originally Posted by hellosailor View Post
I'm skeptical that an aluminum mast will ever have enough induced eddy currents from the earth's feeble magnetic field, to create an additional local magnetic effect on a fluxgate compass.
So was I when I decided to install a fluxgate into my mast. After all, a not so bad choice of location on a steel boat, centred and protected. With a deviation of only 3 this proved to be a not too bad choice. But then sometime the autopilot progressively would lose it’s heading by more than 100 degrees (matter of minutes). This did happen when returning to Auto from Standby after having been in Auto successfully for hours, after a tack and also when swinging on a mooring. Sometime it will reset itself to the correct heading after about one hour, but most of the time when underway it was necessary to use the “Aligning the compass” procedure. After many test (different fluxgates, autopilots and electronic compass) I come to the conclusion that the surrounding aluminium was affecting the fluxgate. Why not after all we have known for decades how to control lines of force.
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Old 09-06-2011, 07:26   #36
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Re: Mounting Fluxgate Compass in Aluminium Yacht

How about (e.g. Raymarine's) recommendation to keep the compass close to the boat's center. I read it - not up the mast or all the way outboard. Not valid?

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Old 09-06-2011, 09:40   #37
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Re: Mounting Fluxgate Compass in Aluminium Yacht

Chala, I hear your point and I also hear "steel boat". Which one do you think is greater, the ferromagnetic boat or the generally non-magnetic mast? Aluminum is generally considered non-magnetic because it takes a significant amount of juice to get eddy currents and significant magnetism in it. If it could affect a fluxgate compass, then it would also swing any handheld compass that came up close to it. And yet, I've never seen a mast deflect a compass. Of course, I've never tried to hold my compass inside a mast, either.<G>

I've seen enough "but that can't possibly" electrical and electronic ghosts that I'd still suspect something else on the boat. Any chance the mast itself is connected to the ground system, and some stray current is using it directly? As opposed to the earth's feeble magnetic field?

barnakiel, the recommendation to place a fluxgate compass in the center of a boat has nothing to do with aluminum or masts. The center of a boat is the point that is least likely to be moving through great arcs as the boat moves in three axes ("axises") so the reading will have the least interference from gross physical swings.
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Old 09-06-2011, 21:54   #38
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Quote:
Originally Posted by hellosailor
Daddle, I was asking about aluminum masts. But apparently I got auto-corrected from "aluminum" to "ali".

I'm skeptical that an aluminum mast will ever have enough induced eddy currents from the earth's feeble magnetic field, to create an additional local magnetic effect on a fluxgate compass.
Eddy currents are not the problem. The unknown has to do with the rotating magnetic field within the sensor that might be attenuated or distorted by the conductive mast. Might...who knows...
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Old 09-06-2011, 23:50   #39
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Re: Mounting Fluxgate Compass in Aluminium Yacht

Aluminum has no effect on a compass.
My boat is all aluminum. The steering compass is mounted in an aluminum bulkhead. The autohelm fluxgate compasses are mounted where they are surrounded by aluminum bulkheads. I use a handheld compass above and below decks. I have a separate compass by my bed. There is no effect from the hull on any of these compasses.
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Old 10-06-2011, 05:56   #40
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Re: Mounting Fluxgate Compass in Aluminium Yacht

See: http://www.raymarine.com/SubmittedFi...ationGuide.pdf
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Old 10-06-2011, 06:43   #41
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Aircraft are aluminum and get hit by lightning, generate static electricity, and run a 440 volt three phase AC current. Any non similar metal contact will cause corrosion, but a pencil is more danger than a penny. Put a barrier between the two(RTV or vasoline or even wax) to reduce this. Aluminum come in different kinds depending on what it is alloyed with and thus electricity acts differently on each kind. Most aluminum will not cause eddys but al6065 has a high copper content and may if it is big enough. I don't know for sir but masts may be made of this because of it's rigid characteristic. I would guess that hulls are probably made of 2024t3 or t6 which have low copper content and very little magnetic interference.
Just my two cent (zinc not copper!)
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Old 10-06-2011, 07:00   #42
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Re: Mounting Fluxgate Compass in Aluminium Yacht

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Originally Posted by barnakiel View Post
How about (e.g. Raymarine's) recommendation to keep the compass close to the boat's center. I read it - not up the mast or all the way outboard. Not valid?

b.
Read again and in doubt ask Raymarine.
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Old 10-06-2011, 07:29   #43
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Re: Mounting Fluxgate Compass in Aluminium Yacht

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Eddy currents are not the problem. The unknown has to do with the rotating magnetic field within the sensor that might be attenuated or distorted by the conductive mast. Might...who knows...
It is also my view; a change of reluctance must produce an unbalance. Mast or vessel both will make a change of reluctance following a change of direction. A round section should be all right anything else will create an unbalance. For screws Duralac.
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Old 10-06-2011, 07:42   #44
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Re: Mounting Fluxgate Compass in Aluminium Yacht

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I don't know for sir but masts may be made of this because of it's rigid characteristic. I would guess that hulls are probably made of 2024t3 or t6 which have low copper content and very little magnetic interference.
Just my two cent (zinc not copper!)
The mast is 6106 T6 or A1 6005 T6.
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Old 10-06-2011, 09:48   #45
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Re: Mounting Fluxgate Compass in Aluminium Yacht

Since Raymarine is showing the mount right ON the mast, it would seem they fully sanction this.

But guys, there's a simpler empirical way to answer this question. Take a modern smartphone, almost any Android or iPhone. There are apps that will read and display the MAGNETIC FIELD SENSOR in the phone, which is a fluxgate or similar device.

Heck, I can use mine to dowse the AC power lines behind sheetrock at home, it picks up the extra magnetic field from three feet away. (Kinda scary.)

Hoist the laundry, make full speed, then go sniffing around the mast with the phone's magnetic field sensor. If there's some type of current flowing down the mast, from static charges or bad wiring or the earth's magnetic field, the magnetic field sensor will pick up the EMI from it. If the phone can't read any EMI, the autopilot's fluxgate sensor won't be seeing any either. (Although the two should interact, unless the fluxgate sensor in unpowered.)

Why debate the existance of gravity when you can sit under an apple tree and watch it happen?
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