Orca3D Holtrop analysis Cp 1/2 of correct value

I am running the Holtrop analysis on a series of boats, and on some but not all of the models the Cp value is 1/2 of the correct value, for example 0.265 instead of 0.230. The stability analysis calculates the correct value. The models are of the entire hull. I have versions with and without decks which does not appear to make a difference.

Has anyone else encountered this problem? If so did you find a fix?

 

I also sent an inquiry to the Orca3D team and received a very quick response.

The Orca3D Holtrop analysis expects a half hull model while I've been using a full hull model. I can easily create a half hull model to solve the problem.

 

Well that's just a stupid limitation. So to use Orca's resistance prediction you have to run it on a half hull?

 

I believe the Holtrop method is limited to transverse symmetric hulls. My guess, and only a guess, is the limitation of using only half hull models in the Orca3D Holtrop analysis is intended to ensure only symmetric hulls shapes are analyzed.