Compass Interference

[pcg]

Has anyone had trouble with nearby electronics affecting a Richie compass? I'm designing the helm station for my boat restoration project and I'd like an old school Richie compass right up front, centered just above the steering column. However, I've read about the potential for interference from a nearby MFD, radar, etc.
How real is this problem? What have you done to mitigate it?

 

[Robert H. Wilkinson]

Paul, you can swing(calibrate) your compass after it is in place and any items that may affect it have been installed. If you just bought it there should be instructions with it. Ideally it can be mounted on the boats centerline but this may make a direct line of site from the helm difficult for reading accurately. The procedure to swing a compass can be found online if they didn't come with it.

I have a Richie compass on both my boats they are a good unit. Can be wired up to illuminate when nav. lights are on. If they leak there is a small plug in the bottom where you can refill them using a medical needle/syringe. If you boat in cold places you can drain it and refill with red RV antifreeze - this also helps with night vision when illuminated. I also carry a hand held "line of sight" compass for taking multiple shore readings.

Apparently the magnetic north pole has been moving at an increasing rate recently requiring adjustments when navigating by compass and plotting your position on a chart.

Regards,

Rob

 

[thataway]

As is said, Back in the Day, we only had compass for navigation (OK a Radio direction finder, lead line, hand bearing compass and sextant)

A compass can be compensated, using magnets in the compass or external magnets. We used to do this in Long Beach CA, with a "Range" on the breakwater. (Measured nautical mile, plus N/S and E/W ranges.)

Other locations you can find or make a range. I do like to check my steering compass before starting a voyage, thus use the sun compass. There are many ways to use an "Internal range"--for a quality hand bearing compass, or GPS compass (Differential two GPS receivers, such as Garmin or Furano ) These are in the $1000 plus range. Good Trimble surveyors GPS compass can start in the $7,000 range and go on up...

Thataway, C Dory 25, had a "Silva hand bearing compass, mounted far enough away that radios, GPS etc had minimal effect. This was the ship's steering compass and could be used as a hand bearing compass. It was aligned with fore and aft boat orientation.



Below is the hand bearing puck I have in ditch bag.




For on land or sea, I have 7 X50 Fujicon binoculars with compass built in, and night illuminated. I also use a military lensatic compass (real military, not the cheap Chinese knock offs.) I also have a Silva Ranger II chart compass to use with Topo Maps. This works better with maps, the Lensatic better for over land navigation...


I have "Sun Compass" which I have used for years to check my compass, and compensate it if necessary, plus make deviation tables. iBelow is similar to mine, basically a reverse compass card, with a long pin in the center. The pin is accurately at right angles to the card, and the card must be level. Azimuth of the sun is from tables (Bowditch, American Practical Navigator is the set I used).

Important to know: Variation (Chart) or Declination (Map) is a magnetic interference common to all vessels from the true to magnet North Pole. This changes, and there are Variations noted on NOAA DMA charts. The rate of change should be noted on charts, and used. When I moved to Pensacola 30 years ago, the "0" ran thru Pensacola, now it is about 1.8 degrees East.

You should know the Variation Declination for your location.

Deviation is a magnetic interference unique to the vessel itself and should be compensated. After the compensation with magnets, then a card of Deviation should be made:

Deviation Card:

 

[ssobol]

Deviation card should also note what equipment should be on or off to be valid if this configuration of equipment is not "normal". For example, radar must be off or VHF not transmitting.

 

[MOOSE]

The magnetic declination map you posted, Bob, is circa 1980. The agonic, or 0 degree line, has shifted west to about where the 4 degree E isogonic line is shown. That’s a shift of about 160 miles west in 40 years. NOAA has a magnetic declination calculator that is rather interesting. One can plug in years and see how the declination has shifted over several centuries. I’m amazed how much it has moved in my lifetime.

 

[Marco Flamingo]

I’m amazed how much it has moved in my lifetime.

I have some old charts that I kept for "historical interest" and was amazed at how much the deviation had changed. They are no longer usable for me as the CD 16 is too small for using a chart and my larger boat doesn't have parallel ruler, dividers, etc. on board. I did keep my nice bronze dividers, again, more for "historical interest."

But I do have a compass on both boats, although I haven't ever swung either. Back in the day, I worked at Captain's Nautical Supplies in Seattle, probably the last business that offered compass adjustment (and maybe still does). I haven't bothered to swing either compass for several reasons. On a C Dory, especially one my size, the compass is basically for "general" direction. It is a small compass, of course, and the markings are in 10-15 degree increments (don't remember). Since a C-Dory is a planing hull, and if on plane, the compass card tends to "dance" such that even 10-20 degree markings are inaccurate. Even off plane, a 16 foot hull isn't likely to be controlled in 10 degree accuracy if there is any chop.

On my trawler, I've compared the compass to the Garmin MFD and the autopilot, mostly out of interest in making sure it wasn't completely off, but not really for recording compass heading accuracy on different courses and creating a record. I have become so addicted to the MFD that compass accuracy isn't that important. Yes, the MFD could go down (and has) at which point 1) I no longer have a "chart" from which to derive a compass heading, 2) I have a phone that I can use for navigation, 3) my wife has a phone, and 4) I usually have a "cruising atlas" covering my area. Of course, the cruising atlas says "Not to be used for navigation," but like a parachute, there may be times when it is the best available solution despite its risks.

I also have a pelorus or "dumb compass" like Bob shows. After taking a bearing, I calculate based on what's shown on the MFD or autopilot, not the compass card. I'm not saying that a compass has no use, but it is way down on the list compared to when I began boating.

I have checked for magnetic interference, turning on and off electronics while watching the compass. I was suspicious when I changed the SD card in my Garmin and the little door over the card snapped shut. Sure enough, it used a magnet to hold the door closed. Opening and closing the door made a 5 degree difference on the compass (which took about a minute to fully reveal itself). I moved the compass from directly in front of me (but still parallel with the centerline) off a couple of feet. That allowed me to move the MFD front and center. I guess that shows my idea as to their prospective importance.

Mark

 

[thataway]

Moose, thanks for pointing this out. I failed to find the most recent charts-

Here is the historical and current variation. This is in a fun geographic form for both place and historical years spanning the use of compasses.

Here is a picture of the compass rose on standard charts (US chart one publication).

Ssobol makes a very valid point- Actually there can be a variety of combinations of light, instruments etc on and change the deviation chart. I make the chart dependent on the most likely combination. Also the old CRT radars, had a lot more effect on the deviation than the modern LCD or LED type of display. At least in my small boats if the radar was on or off made no difference from any other display on the MFD.

All DC wires near the compass should be twisted pair. Compass swung with and with out lights on, with and without all electronics within 3 feet on. The steering compass should be remote from the autopilot compass.

I spent most of my life on sailboats where the only item which had affects on the steering compass was the twisted pair of the compass light: with the compass located often in the wheel pedestal:

We would hand steer night and day by this type of compass in ocean races, often several weeks on longer races like Transpacific to Hawaii.

 

[pcg]

Thank you all. Lots of good info here. Some of these comments now beg the question...

Where to put the autopilot compass?

 

[MOOSE]

Yes, Bob; that’s the NOAA calculator to which I was referring. Most interesting. The agonic line is currently about 20 miles west of where we live on Rainy Lake.

 

[colbysmith]

Thank you all. Lots of good info here. Some of these comments now beg the question...

Where to put the autopilot compass?

Most autopilots recommend center of the boat somewhere low. I have mine located just under the dash in the center (above where you enter the V-Berth). This works great, as long as I don't forget and put my sunglasses, keys, or anything else magnetic on top the dash right there. Including my phone. If I'm careful which way I position my iPad (back up with navionics), I can keep from exceeding about a 5 degree mapshift. :? (Everything else throws it about 30 degrees.) Colby

 

[hardee]

My AP compass is mounted in the port aft corner of the cabin, as far as possible, away from everything else metallic. The KVH is centered over the companion way, but as mentioned, the navigation priorities have shifted over many years.

Harvey
SleepyC