"JAXAshby" wrote in message
...
One
could also say that the compass represents another reference

no, one can not. one can ONLY state which direction magnetic North is and
which direction relative to that the boat is pointed, but *no* deduction can
be
made as to which direction actually is actually going. none.

I never claimed you had absolute certainty with infinite precision about the
direction of travel. You're the one claiming that's the only definition of DR.
In fact, formally speaking, the DR plot by itself makes no such presumption; it
only describes the position based on the ship's heading and speed through the
water. If you had any understanding of DR you would know this. Once again, you
just prove you don't know what DR is.





but that would be
too complex for jaxie.

wasn't too complex for Einstein when he wrote his PhD thesis on the subject.
you can read that thesis, if you want, by looking up The Special Theory of
Relativity.

Einstein's PhD thesis was not special relativity, it was "A New Determination of
Molecular Dimensions." And Special Relativity did not focus on the relative
motion issues that are significant for ship's navigation. That was fully
addressed by Galileo in his "Theory or Relativity" 300 years earlier. Einstein
only mentioned it by way of recapitulating traditional physics before showing
how Special Relativity is different. It looks like this is yet another topic
where you can show your ignorance.