I love this sort of stuff, and know first hand it can make or break a paddling race in certain waters. Here in Vancouver BC we can have 5 m (15 foot) tides at times an this results in very strong currents.
As in surfing, seeking out the fastest line in currents often differs from the shortest line. Even on a Hawai’ian like 1 foot tide…
My favourite resource sites include
Engineered Athlete Services