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Heading sensor on alloy boat

Posted: Sun Oct 07, 2018 12:18 pm
by OceanTrvlr
I have a Garmin GHP Reactor autopilot on my North River RAIV with the course computer (heading sensor) mounted below the deck, under the helm area. It works but I’m not able to get very good compass calibration values. Am I fighting a losing battle with a metal boat or should I be looking for other sources of magnetic interference?

Ethan
NRB Almar 28 RAIV

Re: Heading sensor on alloy boat

Posted: Sun Oct 07, 2018 9:38 pm
by 3f8
Is it consistent or all over the place? Alloy should not be the culprit. Some thing ferrous or electromagnetic. Not all stainless steel types are non magnetic if there are any near. Also on the center line of the boat is best.

Re: Heading sensor on alloy boat

Posted: Sun Oct 14, 2018 6:48 pm
by OceanTrvlr
3f8 wrote:
Sun Oct 07, 2018 9:38 pm
Is it consistent or all over the place?
I’m not sure, I’ll have to experiment some more. It’s primarily the Garmin autopilot Calibration Value in the Dealer Setup menu which concerns me. It’s gives a number from 0 to 100, with 100 being a magnetically perfect environment. Mine is somewhere around the mid 50s and I think needs to be much higher.

Re: Heading sensor on alloy boat

Posted: Tue Oct 16, 2018 2:51 am
by peterbo3
Do you have electric wiring near the sensor? This can cause magnetic interference. One reason why the compass light wires should always be twisted to negate any interference which will affect the compass heading.
If there are hot wires in the vicinity a quick test is to turn off the power if this is possible & check the calibration value. If there is wiring & it is house feed you can wire a smaller battery directly to your panel buss & turn off your house feed then check the calibration.
Alloy is not magnetic so my money is on the wiring.

Re: Heading sensor on alloy boat

Posted: Thu Oct 18, 2018 8:11 am
by OceanTrvlr
Here's the installation below the floor of the helm area, looking aft. I guess I have to admit that the course computer being only a few inches away from the bilge pump wires is probably not good.

Ethan

IMG_4016.JPG
IMG_4016.JPG (132.61 KiB) Viewed 434 times

Re: Heading sensor on alloy boat

Posted: Thu Oct 18, 2018 1:54 pm
by gandrfab
Just because I haven't seen the addressed.
Are you calibrating the compass on the water underway?

Re: Heading sensor on alloy boat

Posted: Sun Oct 21, 2018 9:11 pm
by 3f8
There is probably magnets in the motor. There are shielding materials. Mu-metal foil might work to shield magnetic interference.

Mu metal is a nickel–iron soft magnetic alloy with very high permeability suitable for shielding sensitive electronic equipment against static or low frequency magnetic fields. It has several compositions. One such composition is approximately 77% nickel, 16% iron, 5% copper and 2% chromium or molybdenum.

Re: Heading sensor on alloy boat

Posted: Tue Oct 23, 2018 10:41 am
by OceanTrvlr
gandrfab wrote:
Thu Oct 18, 2018 1:54 pm
Just because I haven't seen the addressed.
Are you calibrating the compass on the water underway?
Yes, underway calibration. I tried the calibration procedure again yesterday with no better results. At this point it's just an exercise in futility since the autopilot is working reasonably well even with the poor compass calibration value. I'll just make do with things as is.

Re: Heading sensor on alloy boat

Posted: Tue Oct 23, 2018 2:51 pm
by gandrfab
Next question (because I don't know) does the unit have or need a magnetic compass?

I haven't helped install, set up a autopilot in years they were Tr-1's.
The compass/gyro, heading sensor was a ball we mounted low on the hull CL mid ship. cough-cough glassboats

Setting them up even in semi rough water was not fun at all.
Consensus was to set them up on very calm days or take them inland to a lake.
And they set up just like the book said they would. Good luck.

Once set the roughest of seas we ever needed to boat in would not phase the autopilot.