You have to start to wonder, 7 knots on a narrow 40 foot vehicle means that it can not even reach its hull speed. Who knows what the engine HP is, but it suggests if that is top speed, the drive mechanism and efficiency is unbelievably poor. I'm surprised they use props. It should really have a jet pump, which would work tons better. The fact they suggest turning the front wheels to help maneuver is kind of telling as well. I'd hate to ever half to dock that thing. Not sure I would want to try it without bow thrusters. The biggest problem though is going to be large flat wall surface. Even a small amount of cross wind will make it heel badly and drift. I could see it would be very easy to be blown off course, especially with it moving so slow.
Personally I would prefer this idea, as the performance will be tons more practical.
http://www.youtube.com/watch?v=YtQdsg28mXg
IRV2