MFDs And Compasses
Hello,
This is the first time I've posted on the list...lurked awhile and have
learned lots from the posts I've read. Thanks to all you posters!
Here's my question. Why do most of the helm stations I've seen have a MFD
and compass way closer than the manufacturers (both compass and MFD
manufacturers) recommended mounting distance? For instance Raymarine
recommends it's "E" series MFDs be placed no closer than 3 feet to a
compass. Every Raymarine installation I see on the net has the compass
almost stacked right on top of the MFD!
I know a compass can be corrected to a degree. But if a compass is corrected
in a magnetic field and the field goes away (i.e. a catastrophic loss of
power) what then? Readjust the compass?
I don't get it.
Any thoughts on this or am I fretting over nothing?
Thanks again,
Steve Jones
Steve, you're quite right, few, if any compasses are mounted far enough from
nearby electronics to avoid being affected by stray electrical currents.
The problem is that installing radars, GPS's, computer displays and other
electronics far enough away from the compasses to minimize their damage
makes them hard to read and use. Why do people do it?
-
Many are totally unaware of the problem and merrily go about installing
more and more electronic goodies at the helm, presuming that's where they
should go. -
And yes, as you say, they see others who have done that and thus presume
that it's correct. -
I suspect the real cause is that few boaters navigate by compass any
more. Sure, they may tell the helm relief, "steady up on 240 and let me
know when we pass the buoy", but as far as actual navigation, they rely on
the GPS, electronic plotting systems, and other sources far more than they
do on the compass. -
Interestingly, when you ask them about it, they will say something like
"Oh, that compass is so far off I rarely use it". Well, yea, duh! -
Like so many other tools on our boats, that only come into play when we
experience massive electrical failures, most rely on their electronics, in
some case the very electronics that are interfering with the compass, to
navigate. And the sad truth is that few would know how to do that if need
be, so the compass ends up being a decorative nautical relic that looks
salty to many.
Bob Peterson
47' Lien Hwa CMY
"Lopaka Nane"
San Francisco
-----Original Message-----
From: trawlers-and-trawlering-bounces+bob=peterson.org@lists.samurai.com
[mailto:trawlers-and-trawlering-bounces+bob=peterson.org@lists.samurai.com]
On Behalf Of Jones
Sent: Saturday, July 09, 2005 10:05 PM
To: trawlers-and-trawlering@lists.samurai.com
Subject: T&T: MFDs And Compasses
Hello,
This is the first time I've posted on the list...lurked awhile and have
learned lots from the posts I've read. Thanks to all you posters!
Here's my question. Why do most of the helm stations I've seen have a MFD
and compass way closer than the manufacturers (both compass and MFD
manufacturers) recommended mounting distance? For instance Raymarine
recommends it's "E" series MFDs be placed no closer than 3 feet to a
compass. Every Raymarine installation I see on the net has the compass
almost stacked right on top of the MFD!
I know a compass can be corrected to a degree. But if a compass is corrected
in a magnetic field and the field goes away (i.e. a catastrophic loss of
power) what then? Readjust the compass?
I don't get it.
Any thoughts on this or am I fretting over nothing?
Thanks again,
Steve Jones
'Lo All,
When I put the radar, GPS, and fishfinder displays on the Celestial,
I plugged them in and turned them on before permanently mounting the
displays. The compass reacted only when the displays were turned on,
and then only at a distance of about 12 inches or less. There is very
little ferrous metal in the displays to affect a compass, leaving
only the magnetic flux set up by the various components, especially
coils. My LCD radar display did not affect the upper helm compass at
all - whether turned on or not - down to a distance of about 6
inches. My lower helm compass is about 15 inches from the displays
(as I recall - not being able to get on the Celestial right now). I
was always intending to properly swing the compass, but never
actually got around to it, but I did make up a little chart showing
the approximate errors. I believe in being able to run on compass
only when necessary, and was confident in my chart.
Later, I installed a KVH autocompass. The KVH and the GPS indicate
almost the exact same headings when underway. The KVH indicated
approximately the same compass errors as was on my old chart. I
"swung" the compass using the KVH on various heading and am confident
that it is now pretty close to as good as it gets.
Based on the above, I believe that the 3' rule is much more distance
than really required.
Take care and be safe.
Wayne
M/V Celestial
Albin43 Sundeck
Wayne, at least you were aware of the issue and took appropriate measure to
minimize it. I note the popularity of extension speakers today for VHF
radios as one frequent source of problems. Why the front-mounted speaker is
no longer popular for many VHF manufacturers, I'm not sure, but those with
top-mounted and bottom-mounted speakers practically require an external
speaker to be heard. And given that most want the radio within easy reach
from the helm, I've seen external speakers mounted within a foot of the
compass, with predictable results. One guy was oh so proud of his
newly-installed speakers, all within a short distance of the compass that I
didn't have the heart to tell him about what he'd done to his compass'
accuracy.
Bob Peterson
47' Lien Hwa CMY
"Lopaka Nane"
San Francisco
-----Original Message-----
From: trawlers-and-trawlering-bounces@lists.samurai.com
[mailto:trawlers-and-trawlering-bounces@lists.samurai.com] On Behalf Of
Albin43SDtr
Sent: Sunday, July 10, 2005 10:53 AM
To: trawlers-and-trawlering@lists.samurai.com
Subject: Re: T&T: MFDs And Compasses
'Lo All,
When I put the radar, GPS, and fishfinder displays on the Celestial, I
plugged them in and turned them on before permanently mounting the displays.
The compass reacted only when the displays were turned on, and then only at
a distance of about 12 inches or less. There is very little ferrous metal in
the displays to affect a compass, leaving only the magnetic flux set up by
the various components, especially coils. My LCD radar display did not
affect the upper helm compass at all - whether turned on or not - down to a
distance of about 6 inches. My lower helm compass is about 15 inches from
the displays (as I recall - not being able to get on the Celestial right
now). I was always intending to properly swing the compass, but never
actually got around to it, but I did make up a little chart showing the
approximate errors. I believe in being able to run on compass only when
necessary, and was confident in my chart.
Later, I installed a KVH autocompass. The KVH and the GPS indicate almost
the exact same headings when underway. The KVH indicated approximately the
same compass errors as was on my old chart. I "swung" the compass using the
KVH on various heading and am confident that it is now pretty close to as
good as it gets.
Based on the above, I believe that the 3' rule is much more distance than
really required.
Take care and be safe.
Wayne
M/V Celestial
Albin43 Sundeck
"Jones" sjones581@comcast.net
At 10:05 PM 7/9/05 -0700, you wrote:
Here's my question. Why do most of the helm stations I've seen have a MFD
and compass way closer than the manufacturers (both compass and MFD
manufacturers) recommended mounting distance? For instance Raymarine
recommends it's "E" series MFDs be placed no closer than 3 feet to a
compass. Every Raymarine installation I see on the net has the compass
Your notions are dead on target. The amount of variant magnetic field
produced by the various pieces of electronic equipment placed near the
steering compass means in practice that the compass is more of an ornament
than a useful device on the majority of modern boats. Notice that the
compass used for autopilot heading has to be placed somewhere else. And
that somewhere is as far as practical from all the fluctuating magnetic
fields from all the wiring at the average helm station.
It is no accident that autopilot manufacturers understand that the compass
has to be mounted remotely to be effective. I once had a big steel boat to
deliver where the autopilot compass was mounted, accidently of course,
between two high powered stereo speakers; which were not fastened down and
slid up against the compass. Naturally the autopilot was nearly hysterical,
as was the captain and crew.
Since I don't have effective control of the deviation near the steering
compass, nor for that matter the autopilot compass, I never assume that
either can be relied upon for presenting a valid heading.
Once upon a time, back in the sixties, I had a charter boat to run where
the compass had 360 degrees of deviation. In other words when the helm was
turned a 1/4 turn the compass would spin on it's top like a child's toy.
Since I did not have radar, loran or gps on that boat, I just waited for
the compass to settle down and would steer by intuition, in the fog while
transiting the Columbia River entrance. By the way, the real navigation was
being done, not so much by intuition as by the use of the depth finder. At
the Columbia the bottom contour has such a distinctive character that we
generally navigated by following depth contours, when visibility was limited.
If it were my own boat that I had control over the installation, I would
sure have the compass as isolated as possible. Either by having a sensor
remotely located with the indicator at the helm station or by keeping the
electronics and electrical wiring away from the compass. Frankly, my
opinion is that unless you are prepared to have deviation compensated for
and a residual deviation card created AND be prepared to constantly test
for newly introduced deviation, then overly relying on the compass for
critical, close quarters maneuvering is not a good idea. I can't imagine a
practical scenario where the crew of the average yacht is going to be alert
enough to identify newly introduced deviation such that they would take it
into account. It is not as if you had a dedicated navigation officer with
several sailors taking visual bearings and checking them against the
compass, like would be done on the average American warship.
Mike
Capt. Mike Maurice
Tualatin(Portland), Oregon