Hello, I have a 1969 85 HP evinrude mounted on a 17ft Winner Marauder boat. I think that my prop either has a bad hub or is cavitating but I am not sure which. We are on quite a weedy lake. On the weekend I was towing the kids around on a surf board behind the boat. For the first run, I took my oldest daughter and we had no problems. On the second run I went on the board with my younger daughter and during this time, the boat would begin to increase revs and lose speed. Once it was throttled back down, the prop would then grab and the speed would increase, but it would begin to slip again. I took the boat out after and accelerated up to full throttle and ran without any problems at all. Does this sound like a prop that is beginning to go bad or could this be a cavitation problem? Any help would be appreciated.