Professional BoatBuilder - February-March 2018

FEBRUARY/MARCH 2018 41

DETAILS: From the Shows

I

remember when electronic components came with

a “Compass Safe Distance” specication. I learned

about it when I had to mount a powerful shnder

with a cathode ray tube (CRT) display overhead sus-

pended from the T-top, to get it far enough away from

the compass. When the “Tuna TV” was dashboard

mounted, the compass—nearly 3' (0.9m) away—went

nuts whenever I turned on the shnder.

I spoke with Ed Sherman, education director at the

American Boat & Yacht Council (ABYC) about elec-

trical interference issues, particularly compass prob-

lems, and we shared similar stories about compass

confusion. Sherman related one about how the mag-

nets in a newly mounted VHF-radio microphone

aected the compass and nearly put him onto the

rocks as he entered his local harbor in dense fog.

Sherman described his methodical approach to

nding compass-aecting electronics:

“Turn everything on and o one at a time, and then

in combination, and see if the compass is aected. I

went so far as to buy a Gaussmeter a few years ago. It

measures magnetic-eld strength, and I found that

many electronics had to be well away from the compass

to stop aecting it. LED [light emitting diodes] and

LCD [liquid crystal displays] are denitely better than

old-style CRTs, but it is always a good idea to check.”

Sherman said about his results using a Gaussmeter

app available for iPhones, “e one I bought seems to

work ne, and the price is so much lower than a ded-

icated Gaussmeter.”

In the main text I mentioned my particular con-

cerns about windshield wiper motors, especially in

smaller boats, where they may be located close to the

compass, with permanent magnets much bigger than

those in a VHF radio microphone. When I mounted

an electric wiper motor on one of my center-console

boats, I noticed deviation on the compass as I brought

the wiper motor close to it. Aer adjusting its location

until there was no compass deviation with the motor

running or o, I thought I was safe. I drilled holes and

mounted the wiper motor. at was a mistake. Once

o the dock I noticed that the compass was frozen,

whether the wiper motor was running or not. e

card would barely rotate, and then it rotated suddenly

aer a signicant course change.

Aer a long, expensive aernoon with a skilled

compass adjuster, I found that installing a 6" (152mm)

riser under the compass head would get the card spin-

ning freely again, and the compass could nally be

compensated.

—Bruce Pfund

Compass Location

Pfund-Details171-ADFinal.indd 41 12/28/17 3:26 PM