I have a digital Gaffrig depth finder in my Bullet with the shoot thru hull transducer. I'm having a problem finding a good spot for the transducer to read. I've placed it in a bag of water and moved it around, it worked for a minute then stopped. I placed petroleum jelly on the bottom and moved it all over with no luck. Anyone have any luck with these shoot thru transducers? I did sand the surface smooth in a couple of areas also, didn't seem to make a difference.