NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
DR formula
From: Doug Royer
Date: 2003 Oct 17, 09:58 -0700
From: Doug Royer
Date: 2003 Oct 17, 09:58 -0700
Axel,here is an explaination of the formula.I use it on a programmable Casio calculator and get the Lat. and Lon. of the calculated DR very quickly.It's always very close to the pos obtained by dividers and rules on a paper chart or DR software.I believe I wrote the formula for Long. wrong.It should be written as delta Long. Lat. = latitude of DR Lf = Latitude of last fix. + - e = time in hrs since last fix. + e for calculating Lat after last fix. - e for calculating Lat before last fix. S/60 = speed in kts./ 60 cos T* = cos of the true course in * ' " Long. = longitude of DR Lonf = longitude of last fix + - e = same as above S/60 = same as above sin T* = sin of true course in * ' " cos Lf = cos of latitude of last fix in * ' " A note about the Longitude of the DR: when useing this formula you will,if travelling in a westerly direction,add the above Long. answer to the Lonf to get the DR long. If travelling in an easterly direction subtract the answer from Lonf to get the DR long.
