Boat Vibration in Direct Drive

I have a real bad boat vibration. It felt like I hit something. I checked the prop, and it didn't have any ding in it. The boat was idling real high that day, that the vibration happenened. I pulled up the floorboards to do some investigation. The front engine mounts very loose (the nut), I could turn with my hand. The rear arm that connects to the rudder seemed loose. I could move it up and down with my hand (is that normal) please help. Im trying to figure out was is causing the vibration.}