I installed a Lowrance Elite-5 DSI color unit with the transducer mounted on the transom of my 1992 Champion 184. It works great until I get up to about 18 mph then I lose the depth and any bottom scan. I started with the transducer abut half way below the bottom of the boat per the installation instructions. I gradually moved it deeper until it was as deep as the bracket would allow. It is mounted approximately 13" from the prop on the right when facing the rear of the boat. I can't move it much further away. I think the problem may be caused by cavitation form the prop but don't know what else to try. I would like to get it so I can get a depth reading at speeds above 18 mph

Any advice you give me would be appreciated.

If you mount it near your drain plug area you will gain some mph before you loose it.

We move all of our transducers up, not down like we used to, into the rising slipstream of displaced water. Many have told us they had grown tired of a transducer with a mind of its own.