I think the most pertinent sentence from the Clyde Winter article linked above is:
"The precise location of the pivot point, why it works, and how the boat moves in response to a force, depends on a lot of things with which we don’t have to concern ourselves right now."
I guess that will have...
In the thread about moving and turning a canoe with side slips, it was mentioned that the canoe's pivot point will shift a little bit fore or aft when the velocity of the canoe changes. The term used to describe this phenomenon is the "peripatetic pivot point". A google search explains this...
I'm curious as to why the pivot point moves as velocity changes. I've noticed this "by feel", as you say, but would like to know the technical explanation.