Hydrodynamic load response

Hi everyone,
The design load criteria for the offshore fixed and floating structure are considered for 100 year return period such as semi submersibles, TLP and SPAR platforms. For ships it’s based on north Atlantic environment and load calculation corresponding to the probability of 10^-8 , which covers the anticipated life of the ship structure at sea. Now my question what design criteria should be followed for ship shape offshore floating structure like FPSO, Drill and storage ships which stay at single location for many days and seems to be valid candidate for load response calculation corresponding to 100 year return period sea state. Please guide on this.
There are some FPSO converted from Oil tankers. How the hydrodynamic load methodology will cause a transformation in that case. Thanks .

 

Simple.

Fatigue.