NavList:

Red,

The orientation of the GPS antenna doesn't affect the GPS readings.  
It's not too difficult to find a heading at which the GPS COG and 
Waypoint bearings match, and the compass bearing is steady, as long 
as you're not passing over any anomalies, such as Robert Eno described.

I remember passing over an electrical conduit or some such in dense 
fog, and the compass commenced spinning.  After we transited a narrow 
channel, I got the boat spinning once the compass had stopped.

Fog is an especial delight for those of us who wear glasses; at least 
I only need mine to read, although that can make it difficult to plot 
a course.

Fred

On Jul 25, 2006, at 5:51 PM, Red wrote:

>
> Bill-
>  Do you remember the days of LORAN C?
>
> Most units had a dampening/averaging factor that was user 
> selectable, i.e. to
> average data and present a display based on the last 10-20-30 
> seconds, etc.
> Consumer GPSes do not, as far as I know, have any similar option. 
> They simply
> perform internal calculations and, if you are lucky, they present 
> "the latest"
> data once per second on the NMEA output bus and the screen. If a 
> vendor chose to
> take longer to average data (like course headings) or used slower 
> cheaper
> hardware that was really using a longer time base to present this 
> information,
> there's no way you would know about it.
>
> So I'd suggest that part of the problem is that both the GPS 
> "heading" and the
> mag compass heading are dynamic displays, and you can't expect them 
> to compare
> until you can freeze both and be sure they are effectively static. 
> With the
> antenna on the boat swinging around...sure, that will be a 
> problem.<G> Compass
> card is swinging too, the twain will probably never meet.
>
>
> >


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