Applying a force to a link in gazebo plugin

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I am trying to simulate an autonomous surface vehicle with an azimuthing thruster. I set up a basic model and want to apply a force to the thruster in the thruster's reference frame. What recommendations do you have for accomplishing this?

So far I have tried:

this->model->GetJoints()[0]->SetForce(0, 300);  // in this method I can't seem to control the direction.  Is it applying a torque and not a force maybe?

and

math::Vector3 force(100,0,0);
model->GetLink("propeller")->SetForce(force);
// this method seems to work, however,  it applies a force in the global x direction not the thruster x direction.