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.



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.