Probably the installation of the shoot thru hull TD. It may be loose, or not far enough back – thus having air between itself and the water. Or the TD itself might be bad.Had that problem with HB setup or prior boats. At low speed it gets the depth from the sv/dv transducer and is suppose to switch to the in hull automatically once on plane.You may also want to verify that the software on the 1198 is current, HB has issued updates to correct problems like this in the past.The most current version is 7.660 (I switched brands a year ago, but you might need at least 7.5** ). I would start with this first, then check the in hull mount. You can also disconnect the sv/dv td from the Y cable and verify you are getting good depth readings at low speed, the high speed consistently to verify the in hull TD is ok.Last edited by catmantwo on February 22nd, 2016, 11:44 pm, edited 1 time in total.Your Signature …