NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Fix Maximum Probability Positions
From: Hewitt Schlereth
Date: 2013 Mar 24, 17:58 -0700
From: Hewitt Schlereth
Date: 2013 Mar 24, 17:58 -0700
John, what I mean by a DR is the boat's position based on the course steered and distance run since the last fix. Just those two things. My experience over the years was that over a period of four or five hours courses were steered pretty accurately, especially on racing boats, where the helm changed every half hour. One person steered a little high; the next a bit low, etc., and resulted in the course aimed for. The biggest variable I found was distance run. But it didn't take too long to figure out the speedo or log was reading some percent high or low, once I had several two-body fixes. I stuck with what my friend called a "pure" DR because it was based on measurements: 1) by the speedo or log for distance; 2) by my observing the telltale compass as the helm went from hand to hand. Because this way of keeping a DR rests on observable data, I always felt it reduced the DR uncertainties as far as they could be. As time passed and fixes accumulated, it became increasingly clear how closely the distances run and courses steered approached the truth. In other words, this method required the least amount of estimation on my part. Hewitt Sent from my iPad On Mar 24, 2013, at 3:42 PM, "John Karl"wrote: > Hewitt, > > Sounds like a semantics question here. By DR position I mean the navigator's best estimate of position when the second LOP was required. In all my figures the DR means the ship's current position from knowledge of factors affecting the ships track and distance made good from the ship's last upgraded position. > > Maybe we are using different definitions of DR position. There are many ways of plotting running fixes, but I tried to use the simplest for discussion. > > Does this make sense?? > John K > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- > > : http://fer3.com/arc/m2.aspx?i=123060 > >