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Subject: Re: DR vs EP vs MPP vs Fix vs Running fix
From: Yves Arrouye (yves@XXX.XXX)
Date: Sat Feb 09 2002 - 18:18:25 EST
> <"The DR position is only an approximate position because it does not
> allow
> for the effect of leeway, current, >
> Is there anyone here who would "reckon" their position without attemping
> to factor in ALL known effects? If one is plotting a DR position while
> crossing the Gulf Stream, even without knowing the current, is there
> anyone who would not indicate *some* offset as a best guess of the
current,
> since they approximate current direction and speed are almost certain to
> exist to some extent?
>
> I ask this as a poll, not as an arguement. My understanding of DR, the
> good Mr. Bowditch aside, was that a navigator placed EVERYTHING he could
> into the DR position and that it was supposed to include all "guestimates"
> of where you actually were, not just ignoring the ones you couldn't
> specify to five decimal places.
This is indeed how I learned it in France. I don't remember having the
distinction. Now, the only thing we used was called point d'estime, which
*is* what you call EP (a good translation too). We did include leeway and
current in our plots.
I am puzzled by the comment about plotting the DR being the "legal track
record" used in case of collision etc. Do you mean that from the DR, and the
time, and everything written in the log book (what sails you had, what
course you did, what the wind was, etc.) one would then work a new plot of
EPs that are as good as possible using all the time needed? Because AFAIK,
if you're having 9 knots of current for a few hours, your DP is going to be
quite far off your real position.
YA
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