You need two. One on the console with navigation and charts. That will allow you to find contours of the lake bottom. The second either mounted on the trolling motor or preferably a trolling motor with the transducer built in. Then you can follow contours or set headings. Bottom mapping capability is nice when you fish lakes for which there are no charts available.

He who joyfully marches in rank and file has already earned my contempt. He has been given a large brain by mistake, since for him the spinal cord would suffice.

- Albert Einstein