My Garmin 150's instructions say to mount the transducer 3/8" below the bottom of transom. I assume they mean the very bottom of transducer? How accurate does the 3/8" need to be? Thanks.

The bottom of the transducer should be 3/8" below the bottom of the hull.

When you drill the holes for mounting, have them in the middle of the height adjustment slots so you can reposition it higher or lower if needed.

 

Most fiberglass bass boats have a stepped transom and the transducer has to be at the lowest level to have water contact when on plane.

 

The 3/8" is a starting point to check for performance. You may get by with it parallel with the hull bottom instead of just below it. It depends on how the junction of the bottom and transom is formed and what the hull's attitude is at speed.

 

Some metal hulls have a weld bead or rivets at the transom/bottom level and the whole transducer would have to be below the hull bottom to get below the aerated water created by those features.

Thanks. I'm thinking of mounting it on my bow trolling motor, but I don't know if it will work. Please see my other thread.