We boarded a rib boat (reinforced inflatable boat) and headed out at high speed out into the fjord. We could see the half-moon before we left, and we were told sadly that the current is strongest during a full or new moon, and weakest during a half-moon. We would be seeing the current at its weakest.
We stopped at several points along the way and an expert guide told us interesting bits of history, culture and geology. Especially interesting were these stone cliffs with undulating ridges:
Here's a video clip of where the current is the strongest, under a bridge. You can see the difference in the water level on either side of the bridge, and the river of water riding on top of the surface of the sea.
The trip was exciting, even if we didn't get sucked into 10 meter wide vortices. As our guide said, it is a twice-in-a-lifetime experience! We'll be back next year...