Dead Reckoning, or the purpose of this blog.

From Bowditch, The American Practical Navigator:

Dead reckoning is the process of determining one’s present position by projecting course(s) and speed(s) from a known past position, and predicting a future position by projecting course(s) and speed(s) from a known present position. The DR position is only an approximate position because it does not allow for the effect of leeway, current, helmsman error, or compass error.

Dead reckoning helps in determining sunrise and sunset; in predicting landfall, sighting lights and predicting arrival times; and in evaluating the accuracy of electronic positioning information. It also helps in predicting which celestial bodies will be available for

future observation.

But its most important use is in projecting the position of the ship into the immediate future and avoiding hazards to navigation.

The navigator should carefully tend his DR plot, update it when required, use it to evaluate external forces acting on his ship, and consult it to avoid potential navigation hazards. A fix taken at each DR position will reveal the effects of current, wind, and steering error, and allow the navigator to stay on track by correcting for them.

That’s my intent with this blog: projecting our current course and speed to see where we, as a nation, are going, and suggesting course corrections. I’m an active-duty Quartermaster in the US Navy, which is to say an enlisted navigation specialist – armies started misusing the word centuries  later. Bowditch is our bible.

Since I am on active duty, I have to include a disclaimer that any opinions here are my own, and any mention of my experience or service affiliation does not constitute endorsement of said opinion by the US Navy.