I have Garmin Echo map plus 73sv. I am loosing DV speed signal at about 25mph. I have an aluminum boat and the transducer is set about 3/8in below hull and is squared with a level. Do I need to move it up or down or is the best it will do. I read some where to have it 1/8in above the bottom of hull. I am happy with my SV imaging. Thanks for help.