Sonar degradation from thru hull mount

Well Phase I of Kayak modifications are done and I may have an opportunity to test the craft as early as tomorrow.  After reading up on the issue and with some common sense I realized that there is likely to be some sonar degradation from shotting through the hull.  It's an issue for me since one of things I want to do this year is shrimp and fish deep down to 500 - 600 ft.

I saw Demonick's post about losing something like one third of his depth range.  I was wondering if anybody else had any experience. I have a PirahanaMax 160 which is rated to about 600ft.  I think my older one got a tad deeper when I used the suction cup mount directly in the water.

I hope to know my results soon, but I was hoping to get some idea on whether I just need to remount in a different location (thinner walls), get another transducer I can just toss over the side when jigging, or upgrade to a higher end FF.

How about the hummingbird kit.  I read somewhere they claim the grease they use actually improves performance.  Anyone have any experience with that?

oops..wrong forum? (edit)