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I think I was a bit behind in my knowledge of GPS+inertial compasses,
there are small low power high accuracy ones now using tow GPS
antennas. Here is an example I found

https://www.vectornav.com/products/vn-300?gclid=Cj0KCQiAh9njBRCYARIsALJhQkFHkcvA-mzk9iQc7Hcu3_7a6yJnu46AwEJbCCbgVZ0pl7v_FOJO8oMaAsTREALw_wcB
I assume they are currently quite expensive but perhaps they will be a
viable alternative to a magnetic compass on a small boat soon.

Of course they rely on electrical power. And on a sailing boat we
still like to have things that still work when you have no electrical
power.

Bill

On Thu, 28 Feb 2019 at 04:48, Mark Coady  wrote:
>
> David,
>
> Most correct, I missed that one, I just often tend to think of collsion 
avoidence more on my radar tracking, spoiled as I am.  A pelorus does the job 
perfectly on visible targets. Risk of Collision:  Constant bearing, 
decreasing range as per COLREGS Rule 7.
>
> The other one I did a poor job noting is the use of the steering compass for 
a maintaining directional stability on a small boat in a heavy sea, 
especially one that slaps you around on the quarter and skews your course 
constantly.  GPS's take time to stabilize heading, vs a steering compass that 
gives you an instant visual and reaction feedback on your countersteer.
>
> You actually use the compass to learn and anticipate the magntude of the 
swing.  You can often tell an experienced helmsmen in a rough sea by his 
smoother track, vs an inexperienced one who doesn't anticipate and correct 
for motions well.  Often overcorrection is the enemy so the vessel is 
constantly yawing about the base track. Its the time delay between the motion 
and response to helm command that creates the problems, with good compass 
work a way to solve them.
>
> 

   

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