For floats issue: make sure you are away from objects. You might have scenery that shows you are in the water but are actually on grass or sand (yes, scenery will register in the sim as having grass, tarmac, concrete, tall grass, short grass, sand, etc). That would explain why its acting the way it does. Slew out to the middle of the lake or try a diff location.
Also make sure your prop lever (blue) is full up or full in. (You might have saved this new plane over another planes save point/location and it might be causing issues from diff options another plane had/has).
Ski's issue: Sounds like low frame rates. This will do the same thing with wheel planes if frames are very low. If the plane is a high resolution and your computer is already maxed out, check frames and see if you are down to about 10FPS. This will be why its bouncing.
Now, if none of those things are in your parameters, then just ignore it, its something else.
Bill