Hard to tell enough from the single picture you posted but it looks like the hull has sponsons that project backwards from the hull on the right (and I assume left) side. Is that true? If so, than you either have to mount the transducer low enough on the flat area of the transom next to the motor mount such that the HDSi transducer can project the right and left Si sonar beams under the sponsons or you will have to mount it on the (less protected) step if there is even enough room for that.
More pictures of the transom of your boat would help here.