Trust me, there are ship/powerboating games on the iPod, but they are hideously gamey or without serious purpose. The physics engine already exists for SSi, but it simply hasn't been put to use. I can't post screenshots because I'm not on my iPod, but there is a quite highly detailed aircraft carrier in X-plane, all that needs to be done really is make it into an aircraft and play with the dynamics a bit until it works.
For a while now, I have been looking at highly detailed models on the 3DVIA app, with no problem.
Like I said, I'm not looking for amazing graphics, I'm looking for a mildly realistic pick-up-and-play ship simulator.