Let’s back up and look at the 2 things that need to be achieved.
The through hull will only function for 2d, and needs to be installed correctly. Location, location, location!. Also, the glass need to be sanded and clean when the puck is epoxied in. I run dual transducers on my boat and pick up nearly everything- including bait, debris, and fish.
Adding the “Y” cable enables the use of the si duper. Again, location, pitch, and no obstruction will give you best results. I have been running it this way since the 1197 was released. Works great. If you don’t get satisfactory results, I would first look at the workmanship of the installation.
Btw, I have a stepped transom, do my big ducer is out of the water at wot. But my through hull still gives me a reasonable signal reception at upper 50’s mph.
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