To calculate the torque caused by the buoyancy force I need the length and the angle but what angle should I use? Should I use the angle of from the center at the bottom of the angle from the center of mass?
you should use angle 2. The buoyancy in this case is due to pressure from 3 sides. the 2 lateral sides undergo triangular pressure distribution that opposes each other and cancels.
Therefore the only effective force is the buoyancy pressure times the surface of the bottom, which is the applied force and is imparted at the center of the bottom of your submerged object.