DS14 and I spent the good part of a Friday morning at Typhoon Lagoon and tried this "water coaster" I'd seen a show on the Travel Channel about the water park in Texas that has a water coaster and I've been looking for a chance to get over there. So this was a "must-do" for us.
Early in the morning there is little wait to try these "coasters" There are three different ones. All start with a steep dip down and a strong water flow helps to push you back up the hill at the beginning. After that, it's pretty much gravity and momentum that carry you through the rest of the ride.
You do ride on a tube built for either two or three persons. Lightest person rides in front, heaviest in back. Try your best to lie across the tube so that your bottom doesn't hang in the hole of the tube. One of the "tracks" has a very steep drop at one point and if you're not lying across the tube, you'll hit your tailbone pretty hard.
All in all, we enjoyed each of the three "tracks" but we wished they lasted longer.
HTH