Originally Posted by rwidman
So a person without a way to measure speed over water would not be a "competent) navigator" ?
Correct, because they cannot tell how far they have come or when (or whether) they will reach their destination
on a long passage
. Fortunately speed over water/ground is easy to get from GPS
. If you only have speed through the water then you also need heading plus estimate of current
(direction and speed) to compute speed and course over water/ground.
I would say that unless currents are very fast such that it affects the safe CTS then knowing speed through the water isn't critical with GPS
available. But it can help in choosing the optimal CTS to reach a destination
the quickest. Sailors with this skill don't have to keep "hunting" for the course that gives the highest VMG. They "know" they are on the optimal course. That makes them a more competent navigator but if someone can't do it I would not say that makes them incompetent.
Please don't let us start a "GPS is gonna' die tack.