I am purchasing 20in transom boat in the next day or so. I have an older evinrude engine which measures 17.5 inches to the bottom of the cavitation plate. I know that this would probably technically be considered a 15in... but I think maybe it is old enough that they were not very uniform on the 15 or 20 standard yet. If my measure tape is accurate it looks like 95% of the prop is going to be below the bottom of the transom and the caviation plate is going to be an inch or two higher than the bottom of the transom. I am not needing performance out of this, it is just something to get by with until I get a long shaft later this year. I am not worried about planing or going fast, especially since this motor is way under powered for the size of boat (5hp on a 16' flat bottom). I will likely be doing trolling speeds 1-4 MPH while fishing. The motor really seems to be inbetween a short and a long by todays standards. I have heard that older motors were often a couple inches off like this. Can anyone give me some expert opinions on this? What should I be watching for when I try it, keeping in mind that I am going to be going slow. Thanks.