The rudder shouldn't be the problem, unless the pick ups are much smaller combined than the one in the original rudder. Mfr02 was trying to help diagnose the problem, just like me. The problem is, without seeing what's happening first hand, we are grasping at straws. The prop shaft issue was a common sense cure, to me, since I use them on my hydroplanes, though I do use nitro motors for power rather than electric drive. Could you post some pictures of your set up, both inside the boat and out, so we can see what you're looking at? It would probably give us a bit more to go on