I have an 85 merc 150 on mine and since I am quite fond of running up on shoals and oyster bars as well as getting stuck at low or wind tide where I have to chew my way back into deep water , I now only run a 4 blade comprop.Its a 13.7 x 18. Sand eats up aluminum very quick and they are not cheap to fix. You can get 4 blade comprops on ebay for 20 or 30 bucks and if you bust off a fin just throw them away .I cant go fast down here anyway because of the shallow water shoals and the sloppy ocean conditions most of the time. I tested the speed in the intercoastal a while back with a hand held GPS and it showed 37 with me , my dog and a full tank of gas and I have bottom paint ..Frank