The base plate is attached to the boat with 3 screws, if these are loose it will move up and down vertically.
The transducer itself is fitted to the base plate by lifting a tab at the top of the base plate and slotting the transducer into it. The transducer is then swung down, pushed down firmly and clicked into place. Then the top tab is pushed down and clicked in. If the transducer is swinging up, than it is not clicked down properly.
Did you fit if or someone else?
I have the same dual frequency transducer and find that the low frequency only works at low speeds, but the high frequency works well up to 25 knots or so.
What do you have the Gain set on? If it is on OFF move it up to Fishing.
Have a look at page 31 bottom right, how does your transducer look? It should be level with or a few m/m lower than the hull.
See how you go with this, otherwise I can take some pics of mine.
Howard.