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» Online Classroom   »   » Public Discussion of Marine Radar   » Radar and verifying the steering compass

   
Author Topic: Radar and verifying the steering compass
Daniel Paschmann


 - posted August 29, 2005 05:18 AM      Profile for Daniel Paschmann           Edit/Delete Post 
Is it possible to check the deviation of the steering compass for a certain course with the help of a (good) radar?
Of course the radar has to be connected to any kind of an electronic compass (like fluxgate).
But are these more precise? I guess not.
Or would it be more precise to create a tripple range and bearing fix (EBL & VRM) with the help of the radar, take the fix over to the map and now compare the compass' bearing to e.g. a ligthouse with the one measured in the map?

Regards from Karlsruhe, Germany,
Daniel

David Burch


 - posted September 08, 2005 02:20 PM      Profile for David Burch           Edit/Delete Post 
Yes the radar can be very useful for checking the steering compass and you do not need the digital compass of the heading sensor to do this. If you have a heading sensor, that might help if you know it is right—in the sense that all compasses should read the same heading—or you might use these same methods to check if that compass is right.

We only need to assume that the heading line of the radar is indeed parallel to the centerline of the vessel. This can be out of adjustment, and it can even drift off in some cases once set properly. But leaving that topic for now, we assume that if we see two rocks lined up in range dead ahead visually then they would also be dead ahead inline on the heading line on the radar screen.

Then if that is the case, we just look up from the chart what the proper magnetic heading is from one rock to the other and compare that with the compass reading. Any difference we observe is compass deviation.

in this case, the very wording of the measurement implies we could have done this without radar, ie the rocks were in line ahead by sight (no radar required)... but back to your question, radar can very often supplement this measurement and make it much more versatile and precise.

the most common example is running parallel to a shoreline or breakwater or large pier. The charted orientation of the object is an excellent reference for compass comparison, but this alignment is not so easy to judge by eye alone. With a quick look at the radar, however, you can see in a moment, that you just need to, say, turn a bit toward the shore and then you will be headed exactly parallel to it, and then you can do your compass check.

We used an example like that in the back of the Radar for Mariners book to check the heading sensor of a vessel and in fact discover that it was quite a bit off.

From: Starpath, Seattle, WA


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