Mount it as far away from the props as possible. Transducers need a clean steady flow of water. If this is just temporary, you don't want to make any new holes in the transom for the cable, so just run it up and into the vent on top of the transom which will get it down into the bilge. You're going to need a very long cable!
Do a search and you should find many posts/replies maybe pics. If you don't have sidescan or fwd scan you shouldn't notice any difference in the first 60 feet with proper and level mounting.