Often the question arises as to whether helical strakes can be considered as stiffening rings in the Stack Analysis.   Generally helical strakes are very thin and not intended to provide stiffness to the structure.  It could be argued that if they are thick enough and attached to the cylinder in a robust manner that they will serve as stiffening rings; however, we have no way to quantify how much stiffness is contributed by a helical strake.  MecaStack software does not consider the strakes to add any stiffness to the structure.  If you can prove that considering a helical strake as a stiffening ring is justified, then you must manually had stiffening rings that "simulate" the stiffness of the strakes.  We can not provide any guidance on how to determine an "Effective" stiffening ring, because we don't know of any methods to quantify the stiffness of the helical strakes.