Last weekend I was following a guy pulling a deck boat. The outboard on the boat had the normal prop at the bottom, but there was a second prop located above the regular prop? The second prop only had 2 blades and appeared to be plastic. At the time I though it might be an integrated trolling motor or something but now it's bugging me and I have to find out what that was. Can any one tell me what it was or what terms to search on google because I cannot find what I saw so far.... Thanks!