[time-nuts] establishing your position w/o gps

J. Forster jfor at quikus.com
Tue Jan 24 13:31:29 EST 2012



[snip]
Then you measure
> distance by tossing a big chunk of lumber overboard with a measured
> rope tied to it.  The captains hated doing math by hand so they
> calibrated the rope by tieing knots at intervals so the natural unit
> was one arc minute at the equator and called it a "knot".

Nope. A knot is a unit of velocity, not didtance.

  A "knot" is 1 nautical mile per hour
  A nautical mile is that distance, subtended at the earth's surface at
the equator, by 1 arc-minute.

If somebody tells you the ship was going "22 knots/hour" they don't know
what they are talking about. A knot/hour is an acceleration.

I've only seen knots/hour used correctly once, in an inertial guidance
system, for cross-track acceleration.

> My buddy who was headed to hawaii put both GPSes in the oven in the
> galley and after three days was able to get one of them to work a few
> minutes  a couple times a day.  That was enough.  But he said he was
> within maybe 15 miles of where he thought he was
>
> Basically your estimated course line intersected with a line of
> latitude gives you longitude.


-John

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