Bulkhead Compass

[Doug J]

I just bought a new Plastimo Contest 101 compass. Can someone tell me how far away from electrical wiring it should be? I was intending to mount it in the bulkhead starboard side of the companionway of my Hunter 26, which is also where the DC switch panel is and wiring for a fishfinder and power for a handheld GPS. I can probably keep the wires about a foot to a foot and half away. Is that too close? Is there a way to shield the wiring to prevent interference?

 

[JohnShannon]

Probably comes with a manual. The wires should be twisted to minimize the area between wire carrying current to your load and the wire bringing current back. You could use coax I suppose if the load is not too large.

 

[Ron20324]

Move the compass from farther to closer and see if it swings any.

 

[Doug J]

I haven't cut a hole yet, but I'd sure hate it f I did that, installed the compass and find out it doesn't work well. I suppose I could somehow position the compass near the electronics (not actually installed) and see what happens. I really want it on the starboard side. Sounds like by your response John, twisting the wires might be beneficial.

Here's a picture of what I have. I would like to put the compass right where those two screw holes are. You can see the switch panel to the left and wiring for my GPS and fishfinder. Those wires can be routed down low to get them further away from the compass location. Do you see this a potential problem, or do you think it would be okay?

 

[JerryA]

I had that exact model on my P23. It was about a foot from the wiring harness that went to the opposite side of the cabin. It did not appear to affect it at all. Positioning by hand as others suggested to check makes sense. Think it will be fine. Nice compass choice too.

JerryA

 

[capta]

As far away as is practical (even if it's only one inch) and mount the deviation card right next to it.

 

[Doug J]

Thanks for the feedback guys!

 

[Ken Cross]

If you intend to check by moving the compass around, make sure everything is running as it would underway.
Often interference with a compass is less than expected, but nasty surprises are common.
Ken

 

[wristwister]

What's that box directly under the switch panel? Stereo? If so, I'd be more concerned about that than the wiring. Make sure you turn the stereo on and have it blaring at full power when you check the compass location for interference.

Do you have a VHF anywhere in the vicinity? That's worse than the stereo for compass interference.

And worse of all, of course, is stereo speakers! I don't see any in the picture, but they need to be FAAAAR away.

 

[Doug J]

What's that box directly under the switch panel? Stereo? If so, I'd be more concerned about that than the wiring. Make sure you turn the stereo on and have it blaring at full power when you check the compass location for interference.

Do you have a VHF anywhere in the vicinity? That's worse than the stereo for compass interference.

And worse of all, of course, is stereo speakers! I don't see any in the picture, but they need to be FAAAAR away.

Points well taken WR! Yes, that is a stereo below the switch panel, the speakers are far away. My VHF is on the port side of the companionway.

 

[CloudDiver]

My compass is in the same position as yours, on a smaller boat, but it doesn't matter since all of my electrical is on the opposite (port) side. I think you will be fine with your proposed location because its not voltage you should be worried about, its the amp draw the nearby wires support that causes interference. The amp draw on your GPS and Fishfinder are miniscule, and your DC panel looks like only 4 circuits and none are probably higher than 15 amps; of which you probably don't get close to pulling the full amount. If it were an AC panel you might have trouble, but you have very low voltage and amp draw on your DC panel compared to that.
I will echo the statements above, you'd have more interference from the VHF, Stereo, and especially speaker magnets... none of which appears to be an issue in your case. BTW, most of my experience from this comes from being in the Navy (massive 440V and 220V cables going through spaces with sensitive electronic sensors), and car stereo installs (massive amp draw). There are some products for shielding cable but you don't need it, the wire insulation is enough with the tiny amp draw they deliver.
I wanted to get the Contest 101 in white, but my cut out is only 3.75 inch where a 4.25 hole is required. I went with the Mini Contest instead. A Ritchie Navigator would just be too huge on my boat.

 

[Doug J]

Awesome CloudDiver. I'm feeling more comfortable making that big hole in the bulkhead.

 

[Doug J]

So, I installed the Contest 101 today. I read the information that came with the compass, but I can't figure out what that small rectangular box is. It's just below the globe. I cut the hole according to the template provided, and that little rectangular box fits in, but I didn't cut it out on the inside, as there was enough room in between. I just don't understand what it's for. Is it for an option I don't have. The rectangular box is of clear plastic, open toward the front, nothing inside. If I would've cut the inside, the plastic would be visible in that rectangle frame, I just didn't see the reason to cut it .
What is it for?

 

[philwsailz]

The rectangular box receives a compensator module, (for lack of a better term) that allows the compass to be dialed in for other global regions. It is in simplest explanation, an accessory that contains two different tiny magnets that can be rotated to readjust the card so it reads level of you intend to use the compass in regions where it's necessary.

Consider this extreme example to understand. You are at the North Pole. Which way does your compass point?

.

 

[philwsailz]

Btw, looking at your pics, nice precision job cutting the hole!!!!

Do you have a void between inner and outer skin like I did? I used filled epoxy to create a non-compressible mounting flange to help insure the compass gasket would seal. Did you use the C-shaped filler piece that came with the compass or did you do something different?

 

[philwsailz]

I didn't like the interior trim piece on mine so I built my own.

 

[Ken Cross]

that allows the compass to be dialed in for other global regions.
.

No No No. Compass compensation is to correct for errors on YOUR boat (Ie. small DC currents that slew the compass off the correct reading or magnetic materials onboard. All boats should have their compass checked and compensated. Here is basically how (this applies to airplanes too.)

Point the boat to a known good compass heading. Don't rely on your GPS for this because it relies an algorithm to convert true to magnetic that won't be necessarily accurate for any given area. but use known geographical points and an accurate chart. Now line the boat up to magnetic North and adjust the north-south compensator to create an exact north (if you can't locate an exact north use something as close as you can get and maintain accuracy. Now reverse course to south and using the North -south compensator split the error in half. Do the same procedure for east west. Go back and check all readings. If the readings now have the same error in all quadrants the compass will need indexed (rotated relative to the boat) and then start over.

If you go to the other hemisphere you need a new compass because the dip weights are weighted to the other hemisphere. This is why in the compasses set at an odd angle if they are in the wrong hemisphere. The dip weights level the compass from the magnetic pull of the earth which reverses on the opposite pole.

Ken

 

[Ken Cross]

I forgot to ask: you did use non-magnetic screws didn't you? Nice looking installation.

 

[philwsailz]

No No No. Compass compensation is to correct for errors on YOUR boat (Ie. small DC currents that slew the compass off the correct reading or magnetic materials onboard. All boats should have their compass checked and compensated. Here is basically how (this applies to airplanes too.)

Point the boat to a known good compass heading. Don't rely on your GPS for this because it relies an algorithm to convert true to magnetic that won't be necessarily accurate for any given area. but use known geographical points and an accurate chart. Now line the boat up to magnetic North and adjust the north-south compensator to create an exact north (if you can't locate an exact north use something as close as you can get and maintain accuracy. Now reverse course to south and using the North -south compensator split the error in half. Do the same procedure for east west. Go back and check all readings. If the readings now have the same error in all quadrants the compass will need indexed (rotated relative to the boat) and then start over.

If you go to the other hemisphere you need a new compass because the dip weights are weighted to the other hemisphere. This is why in the compasses set at an odd angle if they are in the wrong hemisphere. The dip weights level the compass from the magnetic pull of the earth which reverses on the opposite pole.

Ken

Thanks Ken. I was recalling from memory from the on-line literature I had found on the Plastimo site; I either read wrong or forgot wrong. ??? Hah... I realize I am adding together info from two different sources, just now remembering compass deviation data from paper charts.... Somehow I was making the compass smarter than it is in my own mind.

Thanks man!

 

[Doug J]

Phil, Ken,
Thanks to you both. I did use SS nuts/bolts. Phil I really like your wood trim piece looks great! Thanks for the compliment of the cutout. I bought a $35 hole saw just for that.
So, if I understand correctly if I determine I need it, I can purchase a compensatory module and just slip it into that rectangular space - correct?

Oh, I forgot to mention... regarding the void between the inner and outer, I used plastic spacers over the bolts in between, so when I tightened the bolts it did not squeeze the two together and I was able to get good gasket compression for a good seal.