Regarding assumed longitude using intercept method.

[Rumata]

Confusion often arises because people think that the "Assumed Position" is something akin to the dead reckoning position or an estimated position. In fact it is neither.  It is a completely contrived position that the navigator is fully aware is not his actual position, it is just a trial position taken up to use with the tables.

  This is why you start with determining the GHA of the star at the moment of the sight. That is an unchangeable angle. It is what ever it is for the day and time of the sight.  What can be adjusted to get the necessary whole angle LHA from the observer is the locus of calculations -- as if the navigator were to "pretend" he was at at another particular position which happens to yield the whole angle LHA results he requires -- even though he fully knows that he is not at this "pretend" position at all.  And this step is only used because the tables do not list every possible angle for LHA, only whole angles for latitude and LHA thereby making them compact enough to carry aboard even a small vessel.

The "assumed" in "assumed position" means deliberately taken up, not estimated or guessed at, or even calculated by dead reckoning.  It is probably an unfortunate choice of nomenclature as it is so easily misunderstood.  Perhaps it should have been called "the trial position" or something else like "the locus of calculations" but unfortunately it is known the world over as "Assumed Position."

This is why the GHA is found first and then the AP is found from that result, and not in any other order.

PeterB

Agree