Centered on a hole shot plate is the best installation IF your jackplate has enough offset to allow for the transducer's length so the motor does not contact it when trimmed all the way down.
Transducer Shield and Saver has a mount setup for the hole shot plate. It's the aluminum mount plus a wedge to get the correct attitude. If you don't have room, there is an L bracket for attaching it to the side of the jackplate. Contact Transducer Shield and Saver for the correct one that matches your jackplate.
You can just use the included transom mount, but would have to make a spacer between the mount and plate to get the right attitude. 8" is the assembled length of the transducer and mount. The cable comes out of the top of the transducer so you have to allow for managing that.
Humminbird Helix 12 CHIRP SI, 1198c SI, 1198c SI, ONIX 10 SI NT, Helix 7 CHIRP SI GPS G2, SOLIX 12 SI, 360, RC-1