I see from the images that the two planes that cut out 1/4 of the tug are parallel. I guessed that the two planes were 90 degrees apart, in which case, there is only 1 DOF along the intersection of the two planes. That doesn't apply to two parallel planes.
You can put a Remote Displacement scoped to all the edges on one cut boundary and set the behavior to Rigid. Do that on the other end and you will have two points to support that 25% slice of the ship. Each point will have six DOF and you can set all six to 0.
Is it correct that the crane wheels are supported on each side of the opening by that T girder, and that you will apply those loads to the T girders for the analysis?
Two rigid Remote Displacements to support the ship will allow local stress around the T girder to be calculated, but it doesn't properly show how the load is carried by the hull of the ship. The hull is really supported by the hydrostatic pressure of the water. You could add that load, which would reduce the reaction forces at the Remote Points to create a more realistic state of stress in the hull.