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.

 

Just found this old thread and I'm curious, Cp should be the same for half and full model, at least for a symmetrical hull?