Ingrid Machecler
Ansys Employee

Good morning, 

1) the thickness of the plate should at least be the size of an element for the meshing to happen correctly. 

2) you will need to add a point mass & moment of inertia to account for the mass properties of what would be the plate. Then the hydrodynamic properties (drag, added mass) would be modelled through your various Morison elements so there is no need to set a thickness value for them. You ring can be modelled with overlapping discs. You would need to ensure is that the sum of the discs area is equal to the real world area of the skirt. 

I guess you don't need to implement both solutions: it could be one or the other.

I hope this helps.

Kind regards,