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Yeah well, as I suspected from the beginning, this is where we part company. I 
prefer to base the DR solely on two things - course and distance - because 
they are underpinned by instruments - course by the compass, distance by the 
log. 

I don't take into account factors like leeway, currents, sea state, etc till I 
have an LOP. Then and only then, do I judge whether those other factors 
reasonably account for the gap between DR and LOP. 

Hewitt


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On Mar 25, 2013, at 7:02 PM, "John Karl"  wrote:

> Hewitt,
> 
> As I said it's the best estimate of the the track over ground, which 
includes all factors that the navigator has available, or cares to use -- 
course steered, distance logged, currents set & drift, leeway....
> 
> Greg,
> 
> OK, great.  Then you've used the EPRF that I've been discussing, middle 
figure in my post 23074.  So then you used that same offset to east to plot 
the 1100/0900 sun line RFIX.  Right?
> 
> If so, then this particular traditional running fix gives good agreement 
between the estimated-track made-good and the updated LOP.  The estimated 
position running fix (EPRF) would give the same result in this case.   (They 
would also agree when the two LOPs are are right angles.)  So I don't get the 
point.  Are you showing how well the EPRF works?? 
> 
> It's when there's a disagreement that the TRF fails and the EPRF gives 
superior results.  Check the 2nd and 3rd figures in my 23074 post. 
> 
> JK
> 
> 
> 
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