Rigging a sonar on a Pungo

Hi everybody,
I just rigged my Pungo 140 with a depth sounder. The removable dash is really sweet on this kayak. I mounted it in the middle section of the tray, in what was usually supposed to be a bottle holder. I then tried to mount the transducer as a shoot through hull by making a foam frame for it and mouting the frame in the bow right in front of my feet. It works great, however, I have however had a problem with my display. The Sonar picks up the hull as a solid interference on the surface resulting in a black line on the top part of the screen. I was wondering if anybody has a good idea how to get rid of this bar or at least lessen its intensity. I guess the problem is the V-shaped hull of the kayak at that position. I also mount my transducer in water, since I was afraid of mounting it permanently from the beginning on. I wonder if the different densities of the medium could cause the black bar issue. Have not tried vaseline instead of water yet, and am not quite sure if I want to commit to mount the transducer permanently. Would consider i though if someone can tell me, that the interference gets less.
Any idea would be appreciated.

Tags: Kayak, Pungo, Sonar, depth, finder, fish, fishing, sounder