Problem with Kalman filter initial condition

Hi to everybody.

I'm facing this issue:

I have the plant that I will provide in the picture. It's a very easy plant!! I have a buoy going on the sea surface with a constant speed on a line.

In my kalman filter i put a giant Q and a low R in order to see how my theoretical model works! And it works horrible.

So i tried the same plant with a state model rapresentation, and it works fine.

I think it's a problem of initial condition, i put some values, but i see them only for the first step.

So i cannot put an initial velocity for my buoy without adding any external force!!!

Thank you in advance