Been there, done that. Andy Zimmerman, owner of the complany (he owned Wilderness Systems prior to Legacy, already throught of the. He told me that underwater obstacles pretty much are no problem. Most of the time, the pedal/prop assembly just lifts out of the way. Plus, there's not a whole lot of prop that's even expose since most of it is in the tunnel of the Ultimate. Did you forget the Ultimate is tunnel-hulled?