When I bought my boat it came with a Lowrance x-47 on it. The previous owner had installed it himself I think. I'm having problems with it on the water. When I'm trolling or moving fairly slowly it seems to be getting a reading most of the time - but not all the time. Whenever, I start the motor and am below wake speed - it gets a reading about half the time. I'm having problems with it finding the right screen setting - it bounces back and forth between 10 an 20' screens quite a bit. When I open it up and pick up speed it loses the bottom completely.

I'm guessing this is all because it was mounted in the wrong place. It is mounted about 18 inches from the center of the boat and about 16" back from the outer edge. The problem I would guess is that it is mounted about 1" above the bottom of the boat. I know mounting instructions say to mount it so that it hangs below the boat to avoid as much interference as possible.

I don't want to move it (and have those two holes in my boat) unless necessary. Is there something else that could be the problem other than the transducer location?

If it's that far up off the bottom of the transom you're getting a lot of turbulence along with air once the boat starts moving. Those skimmer type transducers need to be below the water line. Try and find a flat part of the underside of the hull to mount it to. I've found if it's mounted around a chine you can get turbulence that interupts the reading. Understand though that those outside hull mounts will eventually lose the reading as the speed increases. It's very hard to find a spot on the transom that won't cause the finder to lose signal once you're up on plane.  The only was to completely fix the problem is with a thru-hull xducer.

I've found it to be A LOT easier just to put the transducer in the bilge area where it has a straight shot down through the glass.  This is assuming your boat is fiberglass.

Here's a link to the Lowrance site: http://www.lowrance.com/tutorials/transducerguide.asp and a link regarding installation: http://www.lowrance.com/support/installation_guide.asp.

You also might want to try angling the transducer up a bit so that when your boat is running at speed, the transducer is level.