If your Piranha 5 worked fine with the transducer in that location than I would certainly try the CSi transducer from the 598ci HD Si there as well. Do you know how much clearance there is in between the lower unit on the motor and the transom, when the motor is trimmed all the way down? You may have to end up trimming the motor up a little to keep from blocking the right Si sonar when using it.