Compass Questions
After boarding thousands of vessels of all types and sizes in the New York and Long Island area we at North Sea Navigator have put together some of the most commonly asked questions we hear regularly regarding the magnetic compass. Questions about Compass installation, compass repair and compass adjusting. We are here to answer any questions you may have and look forward to servicing all your compass needs.
No question is ever too small!

With G.P.S. on board why do I need an outdated Magnetic Compass?

This is certainly the most commonly asked question from the push button, modern day navigators aboard a broad spectrum of vessels today. The compass has been referred to as obsolete, old fashioned, unnecessary, out dated and a dinosaur.

Consider this, the very instrument that got Columbus and countless other explorers around the world still exists for a very good reason….IT WORKS!
The fact is the magnetic compass is the most uncomplicated, inexpensive, easy to use and reliable instrument on your boat. Why wouldn't you want one? Although GPS is a very helpful piece of electronics it has its limits and should not be relied upon solely for directional information or considered a replacement for a magnetic compass.
See article "A Compass (still) Saves the Day" Many boaters are under the incorrect assumption that their GPS has a compass built into it this statement is in accurate.

A simple test can be done on-board to disprove this theory

1) Take your boat to a place where it can safely be maneuvered at idle speed

2) Point the boats bow roughly north, and put it in neutral, now take note of the course heading on the GPS.

3) Next give a touch starboard power, slowly turning the boat to a westerly direction. What does your GPS heading

    read now?

4) Continue to the left checking the display as you rotate around a 360 degree turn. The GPS is not capable of giving you an accurate up-to-the minute course heading because it is not covering enough “course over ground”. It displays the heading of where you have been, not the heading you are currently on. Now picture being in fog or other poor visibility conditions,the same outcome could be disastrous with no directional reference.

GPS’s vulnerabilities include:

 Operator error due to incorrect data input
 Blown Fuses or loss of electrical power
 Interruption of signals by the US military for security purposes
 Solar flares can disrupt GPS signals

What does it mean to have a compass adjusted, calibrated or swung?
A compass adjusting procedure is done by using a known directional reference. These can include a sun azimuth or a known land bearing, for example: a tower or tank. This directional information is used in conjunction with a pelorus. The necessary corrections are then made to the internal correctors, and a deviation table is prepared to record any remaining errors if any.

Is my Compass Pre-adjusted by the Factory when it was built?
When a compass is built by the manufacturer it is done on a workbench which is basically a magnetically clean environment. At that point it is set for the basic North, South , East, West headings and is generaly accurate.

It is then purchase and installed by an owner, boat dealer or builder.
That is when things can change drastically.
As well as the compass being installed, usually a variety of electronics surrounding the compass are also installed and powered by a rat's nest of wires. These electronics when turned on can deliver an electromagnetic field which of course will negatively affect the accuracy of the compass.
Next let's not forget those stereo speakers, which are basically what? You got it a very large magnet!

In short, the answer to this question is NO...by the time your compass gets to you a number of things have already created what is known as DEVIATION (an outside disturbance which deviates the compass from the Earth's magnetic field) which needs to be compensated for by a qualified compass adjuster.

Is my compass adjusted by the boat builder or dealership before I take delivery of a new boat?
This is a dangerous assumption. In most cases the answer is no. It is safe to say that the builder does not adjust the compass based on the fact that all equipment has not yet been installed. If your dealer has had the compass adjusted for you, a completed deviation table would be furnished.

What are the common instruments that can create errors?
VHF Radio, Radar, Loud Hailers, Tachometers, Gauges, Stereo Speakers,

Engine Room Blowers, Instrument Panel and Wiring to mention a few!

Can I shield my compass from any of the above mentioned disturbances?
Take a moment to think about the result of being able to shield the compass from a magnetic disturbance. This action would succeed in shielding it from the Earth's magnetism, which is the very thing that makes the compass work to begin with.

When is a compass in need of repair?
1. When there are cracks in the dome.
2. When fluid levels are low, creating a bubble or fluid is all together empty.
3. The dial or card is discolored or yellow.
4. When the dial begins to stick * follow these steps to test dial.........
While dockside take note of the compass heading. Hold any magnetic object to the compass so that the original heading is deflected about 10. Remove that object, and see if the dial returns to it's original heading.
Repeat this several times deflecting the compass to both sides.


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