Escapee, if your not getting a reading on plane check the transducer (how it was mounted) it should be 1/8 to 1/4 of an inch below the hull, angled "slightly" forward and perfectly level starboard to port. Also, if it is directly in-line with any strakes/chines or thru-hull fittings the airbubbles that those things create will affect the reading.
One other thing to check is the scroll speed setting, it should be set on fast, if its not, that could be your problem.