thanks for your reply.
In the simulation, the mass of the robot is assumed to be 11.5 kg according to the technical information given on the site. I assumed the body device on the center of the robot’s buoyancy and the center of mass is 2 cm lower than the center of buoyancy.
I assumed the moments of inertia, added mass coefficients and drag coefficients according to the attached article.
What happens during the simulation is that after a short period of time, the values of the linear and angular velocities, along with the Euler angles, tend to infinity.
reference article: