Has your friend or yourself ever had the pleasure of trying to tune a sat? If you had I'm sure you would realize that a dish on a boat would be an impossibility. Even on the calmest waters, Im sure the boat would be moving slightly, and even the slightest changes in dish direction can cause total loss of signal. Motors are not designed to track a specific sat if the dish moves....they are designed to move a dish in an arc pattern across the sky in order to receive different birds that are all located along this same arc.
When he said motorized, I would assume he meant one of those tracking dishes for RVs and motorhomes that keeps a lock and moves the dish as the vehicle moves. While I'm sure that would theoretically work fine on the calmest of water when at the very least you might be moving north/south/east/west and only very slightly up/down, you'd probably run into issues on choppy water where the dish couldn't track the satellite quick enough.