autopilot compass placement, where is yours?

[vas]

the final pieces for my autopilot puzzle arrived today, so had a good look around trying to find a suitable spot for the compass ball thing of my Garmin GHP10 (aka CCU)

Theory has it that it's got to be away from metallic /magnetic things (or fields created by electric cabling), along the centre of the boat and close to the COG.
I'm trying to be reasonable and anyway the compass has to be within a few metres from the lower helm position as that's where some of the wires end up (yes I know I can extend them as they are not on a fancy propriatory plug)
This means that from lower helm and aft it's a no go area as we have lots of metal on the steel diesel tanks (across the full width of the hull under lower helm) then we have two tons of engines, gearboxes and genny on the one and batteries on the other side.
Further aft we have two 250lt steel tanks for fresh water a watermaker on the one side and the pump/rudder ram on the other.
Further aft we have the hull and the sea...

So going towards the bow now
just in front of the tank/cabins bulkhead we have a nice big aircon unit and a big bugger seawater pump for it.
As we go fwd, at bilge level (or thereabouts and definitely under the cabins/corridor floor) we do have a couple of bilge pumps a massive Rheinstrom black water pump and a meter in front a whale gulper on the greywater tank.
Further on we have another meter or so and we reach the 40kg bowthruster and it's huge cables. and we're not talking about going to the anchor locker further on, are we?

Nice,

I know I have to do the doughnut routine to calibrate the compass, but I'd rather not have it stuck in the wrong place to start with.

• Best spot (that's reasonable wont need me dismantling half the boat) is on the bilge in front of the aircon and to the stbrd of the black water pump. No cabling around, rather low, dry and hopefully not close to any spot that daughter will decide to leave metal ornaments sitting on her cabin floor... Still a metre from either items mentioned.
• Alternatively, stbrd side at hull on the ceiling of daughter's cabin. Only plywood, epoxy, mat, ss countersunks around and a bit of aluminium railings (again with a M10ss bolt and nut. Means I get to almost 2m away from all metals and reduce the danger of accidental storage of metallic things close by. However I'm within .5m of el fields from the N2K bus (should be zero!), cabin lights cables and bow anchor light and bowthruster massive copper cored cables. I understand that I'm not going to be on a/p route w

hen using the bowthruster, so I'll skip that, but I wonder how strong the fields from a few amps across wires will be on passage.

Anyway, so where is your compass installed and did you have any issues in calibrating?

cheers

V.

 

[maby]

Ours is in one of the bench seat lockers in the lounge, right next to the sub-woofer! Clearly this is about as bad a position as it is possible to imagine, but it was put there by a professional Raymarine trained engineer and it appears to be accurate to within a degree or two in all directions - so I am forced to conclude that the sub is very well magnetically shielded!

 

[Blue Sunray]

In the saloon deckhead towards the aft end no apparent issues, unlike the magnetic compass on the upper helm which is useless as far too close to the AP and other instruments.

 

[vas]

In the saloon deckhead towards the aft end no apparent issues, unlike the magnetic compass on the upper helm which is useless as far too close to the AP and other instruments.

hm, never thought of the deckhead although on a f/b boat that's way above the w/l and far away from the COG. However routing cables will be a nightmare, so not so keen. Could try mounting it under the sundeck, ie ceiling of bow cabin or corridor, away from all metals, plenty of space that's where I have my gps mushroom hidden (and works fine!)

Ours is in one of the bench seat lockers in the lounge, right next to the sub-woofer! Clearly this is about as bad a position as it is possible to imagine, but it was put there by a professional Raymarine trained engineer and it appears to be accurate to within a degree or two in all directions - so I am forced to conclude that the sub is very well magnetically shielded!

or the sub is not working at all
interesting placement nevertheless.


cheers

V.

 

[Divemaster1]

Ours is fwd of helm position underneath the windscreens ... accessible via hatch in ceiling in the companion way... (think you know what I mean), but not sure what you have done here during your rebuild...

 

[vas]

Ours is fwd of helm position underneath the windscreens ... accessible via hatch in ceiling in the companion way... (think you know what I mean), but not sure what you have done here during your rebuild...

I'll rather skip that spot Alf as plan is to have a large drawer there for cutlery and what not. ATM it's empty and only has symmetrically place the two wiper motors. The other option under the sundeck is just a metre or so away, so may do that at the end

cheers

V.

 

[tillergirl]

I'll rather skip that spot Alf as plan is to have a large drawer there for cutlery and what not. ATM it's empty and only has symmetrically place the two wiper motors. The other option under the sundeck is just a metre or so away, so may do that at the end
V.

On my wooden yacht, the compass 'thingy' is under the chart table. Placed some cheap cutlery in one of the drawers under the chart table and the deviation was 'wow'. So obvious fortunately.:encouragement: SWMBO could alter the deviation by opening the drawer a little, a little bit more, a lot! Best now only use the best stainless cutlery!:encouragement:

 

[prv]

When we bought the boat, ours was in one of the under-bunk lockers in the saloon. One day my dad put a load of beer in steel tins in there, with predictable results

I've moved it to a void inside the structure of the saloon table - essentially it's screwed to the forward side of the forward table leg, though inside a sort of fairing of thin ply. As long as nobody tries to store an anvil on the table while we're under way, it's hard to see how a lump of metal can get within a couple of feet of it.

Pete

 

[Divemaster1]

I'll rather skip that spot Alf as plan is to have a large drawer there for cutlery and what not. ATM it's empty and only has symmetrically place the two wiper motors. The other option under the sundeck is just a metre or so away, so may do that at the end

cheers

V.

Fair enough... our wiper motors are at the top of the windscreens, so well away... Got 14 lifejackets in that space ourself between Stb and Port side, so nothing that really can interfere...

 

[vas]

an update...

Decided to stick it under the steps going down to the cabins just over half a metre of anything metalic (air con, diesel tanks)

Turning on the a/p (on standby) plotter picks the heading sensor as it calls it (they are all Garmin and on the same NMEA2000 network so information flows from one to another) and orients the boat icon correctly on the floating pontoon.
Turning it by hand has the boat icon rotate respectively.

Effectively, all seems fine and happy.

Went out today for a swim with the wife and tried to do the on water calibration (have done the dockside one before)

When it reached the now make clockwise turns at a rate of 1 full turn in approx 2mins, I did it and if failed (after completing the 3turns it specifies.

Went ahead and did it a second time more carefully (checking on the plotter that circles look like circles and are slow enough (if you're too slow it pops a warning anyway). Failed again!
Got bored, went to a small private rocky bay swam, read newspapers, ate, read a bit more, sunbathed and decided to go back to port.
Had another go and unsurprisingly failed again.

Now, anyone got any pointers?

For the record its a brand new GHP10 system I've put together buying all the bits new on ebay one by one at less than half the cost of the complete package.
Needless to say system boots, pump is working fine and even the zig-zag pattern it did after the failed compass message, worked fine.

Cheers

V.

 

[MapisM]

As I understand, the instrument works just fine, and also the calibration procedure is initiated correctly.
That leads me to think that there are no hw/sw faults, but it's "just" the calibration self-check that does not evaluate the process accurate enough, hence eventually rejects it.

Now, based on a few calibrations I made and on my understanding of the manuals (though I only did that with Furuno and Raymarine stuff, never with Garmin), the reason can fall either in one or the other of these two categories:

1) some magnetic bits are too close to the heading sensor. The calibration is meant to compensate also these things, but within limits. If the deviations are too high, the calibration is considered void.
Incidentally, potentially this could be due also to some external magnetic interference (like high voltage electric cables on the bottom, or whatever).

2) too fast/too irregular circles, but it sounds like you are already aware of that.
Mind, also the sea surface has to be dead calm, because if the compass senses even the slightest reverse in the rotation (i.e. CCW instead of CW), the calibration is rejected.
And even assuming that you actually keep steering CW, if the sea motion makes the boat roll or pitch, the compass can sense a rotation reverse, even if by just half degree or whatever, and even if just for a second.

Bottom line, I would keep trying, after checking with a manual compass that you don't have metallic interferences near the heading sensor, looking for optimal conditions, and being very careful while making the slooow circles.
Fwiw, I've seen calibration failing because the circling was too fast, but never the opposite.

 

[vas]

As I understand, the instrument works just fine, and also the calibration procedure is initiated correctly.
That leads me to think that there are no hw/sw faults, but it's "just" the calibration self-check that does not evaluate the process accurate enough, hence eventually rejects it.

True, the other portions of calibration (going on a straight line, doing the zig-zag by itself etc) are just fine.

Now, based on a few calibrations I made and on my understanding of the manuals (though I only did that with Furuno and Raymarine stuff, never with Garmin), the reason can fall either in one or the other of these two categories:

1) some magnetic bits are too close to the heading sensor. The calibration is meant to compensate also these things, but within limits. If the deviations are too high, the calibration is considered void.
Incidentally, potentially this could be due also to some external magnetic interference (like high voltage electric cables on the bottom, or whatever).

2) too fast/too irregular circles, but it sounds like you are already aware of that.
Mind, also the sea surface has to be dead calm, because if the compass senses even the slightest reverse in the rotation (i.e. CCW instead of CW), the calibration is rejected.
And even assuming that you actually keep steering CW, if the sea motion makes the boat roll or pitch, the compass can sense a rotation reverse, even if by just half degree or whatever, and even if just for a second.

Bottom line, I would keep trying, after checking with a manual compass that you don't have metallic interferences near the heading sensor, looking for optimal conditions, and being very careful while making the slooow circles.
Fwiw, I've seen calibration failing because the circling was too fast, but never the opposite.

P.,
sea was as flat as a flat thing, only the ripples of me going in circles at 6kn to bother...
Couldn't get the a/p software give me a warning message on too fast circle, did get too slow though. Throughout the test a/p control message was "just right" which probably means I've covered the speed and curvature right.
I'm getting good at circling around as on the third attempt two of the three circles (as seen on the trails on the plotter zoomed in) were smack one on top of the other

Before placing the compass there, I loaded a digital compass app on my smartphone and was going around the bilges and cabin ceilings like an idiot trying to find deviations... It was placed on one of the quitest spots. I'll check again with another magnetic field application if there's something odd there and temp place it somewhere else and see. Did my tests, placed the compass ball and then replaced the steps from the salon. I just wonder if there's enough metal on the steps to affect it, but I really doubt as it's timber with a few screws and nails.

I'm more worried on what the others see as an idiot going in circles to no end (circa 6mins for each failed set...) and getting a empty enough space with no fishing boats passing by.

OK, w/e will be the next test then.

cheers

V.

 

[guernseyman]

In my centre cockpit boat there seems to be metal all along the c/l; eventually I settled on the after cabin bulkhead away from the c/l. There is still a significant deviation so I ignore the compass readout and adjust according the GPS track or visual sighting as appropriate. No problems.