It's literally one of my favorite songs in the world, but even if it weren't already a fave it's superfun to beatbox the tune with your son slightly rapping it.
I estimate the boat speed to be somewhere between 0.00001 and 0.00002 MPH. Or, until the song has played at least 873 times and I'm ready to check myself into some facility somewhere that does things to people - anything involving not playing that song is ok.
And yes, to answer your question, I was once stuck on that ride for about 20 minutes in the late 1980s, and yes I am still recovering. (But I'm doing much better! )
The only two speeds I have ever experienced were slow and stop for the boats. The latter being the pileup of boats bumping into each other waiting to reach the disembarkation area.
Maybe they had replaced the squirrels in the cage that power the ride that day.