Sorry, let me hijack the thread slightly.
Let me remind everyone that while a GPS is good at telling you where you are to some reasonable precision, GPS signal alone cannot tell you your heading. Global Positioning System, not Global Heading System... Even under way, a GPS device will tell you your course over ground as a compass bearing, but it will not tell you where your bow is pointed. Consider backing in reverse as a simple example of where the GPS bearing will differ wildly from an adjacent magnetic compass. Also consider traversing a current, or pointing/pinching high while slipping, where you have adjusted your heading to correct for the external factor to give the COG you desire.
Flux-gate, or traditional, a compass is going to be affected by any ferrous materials in reasonable proximity that can affect the way the magnetic flux field intersects the compass. When you move ferrous materials about on a boat you will affect the compass reading... To what extent is dependent on many factors, size, relative location, distance, etc. This is why even a simple magnetic compass has a mechanical/magnetic means of correcting for actual mounting, to compensate for the effect of other magnetic or ferrous materials onboard.
As a loudspeaker provider to the marine induistry, I am keenly aware of what happens when you introduce magnetic materials or potentially magnetic materials to a boat....
"Sir, why regardless of which way I steer does the compass point due south? It is warm; I know we are not at the North Pole..."
Let me remind everyone that while a GPS is good at telling you where you are to some reasonable precision, GPS signal alone cannot tell you your heading. Global Positioning System, not Global Heading System... Even under way, a GPS device will tell you your course over ground as a compass bearing, but it will not tell you where your bow is pointed. Consider backing in reverse as a simple example of where the GPS bearing will differ wildly from an adjacent magnetic compass. Also consider traversing a current, or pointing/pinching high while slipping, where you have adjusted your heading to correct for the external factor to give the COG you desire.
Flux-gate, or traditional, a compass is going to be affected by any ferrous materials in reasonable proximity that can affect the way the magnetic flux field intersects the compass. When you move ferrous materials about on a boat you will affect the compass reading... To what extent is dependent on many factors, size, relative location, distance, etc. This is why even a simple magnetic compass has a mechanical/magnetic means of correcting for actual mounting, to compensate for the effect of other magnetic or ferrous materials onboard.
As a loudspeaker provider to the marine induistry, I am keenly aware of what happens when you introduce magnetic materials or potentially magnetic materials to a boat....
"Sir, why regardless of which way I steer does the compass point due south? It is warm; I know we are not at the North Pole..."