Resistance prediction methods for asymmetric hard-chine planing catamaran

[AndreaSaiz]

Hi everyone,

I'm currently working on the hydrodynamic design of an asymmetric hard-chine planing catamaran, and I'm hitting a wall regarding the early stage resistance prediction. The operating regime is 1<Fn <1.7.

I initially reviewed the work by Ghassemzadehahrami et al. ("Development of a Mathematical Model for Performance Prediction of Planing Catamaran in Calm Water"). While their mathematical model is robust, it is strictly validated for the high-speed planing regime (Fv > 4). My design operates strictly below that threshold, putting me in the transitional/early planing regime where their formulations break down due to wave interference inside the tunnel.

I am considering adapting Savitsky's method or using Morabito's semi-planing/planing empirical formulas. However, adapting these symmetric monohull equations to an asymmetric demihull presents a severe limitation: deciding which deadrise angle to input without destroying the validity of the dynamic lift and center of pressure calculations. Averaging the deadrise seems like a massive oversimplification that ignores the asymmetric lift vectors.

My Questions:

1. Is there any reliable empirical or semi-empirical method (or modified Savitsky approach) specifically adapted for asymmetric planing hulls in the transitional/early planing regime (Fv < 4)?
   
   
2. If I am forced to use Savitsky to estimate the bare hull resistance of a single asymmetric demihull as a baseline, what is the most scientifically sound approach to input the deadrise angle?

Any references to technical papers, systematic series (beyond symmetric VWS), or personal experience with this specific geometric headache would be highly appreciated.

Thanks in advance.

 

[baeckmo]

Always good to go back a bit.....:

A/ Journal of the Aeronautical Sciences, june 1954: pp 419, Savitsky andd Dingee; Some Interference Effects Between Two Flat Surfaces Planing Parallel To Each Other at High Speed.
B/ J. Hydronautics Vol 13 no 1, pp 31, Liu and Wang; Interference Effect of Catamaran Planing Hulls.
C/ AIAA Journal October 1982, pp 1461, Lee; Interference Factor for Catamaran Planing Hulls.

Good luck!

Edit: Come to think of it, forum member Ad Hoc presented relevant model test data some time ago, if he doesn't chime in, contact him (since I do not remember where to find it),

 

[bajansailor]

This paper is about the resistance components of high speed displacement catamarans, not planing, but there might still be some information here that is relevant to your project?

https://www.researchgate.net/public...ponents_of_high_speed_displacement_catamarans

Have a look also at this thread from a few years ago -
Resistance prediction methods/series for catamarans https://www.boatdesign.net/threads/resistance-prediction-methods-series-for-catamarans.64163/

 

[Dolfiman]

You can also have a look on my VPP proposal for a power catamaran, especially the last version documents attached to quote#8. Can be helpful for a speed prediction at an early stage, but to note that this does not address asymetric hull specifically :
SA-VPP power catamaran https://www.boatdesign.net/threads/sa-vpp-power-catamaran.65725/#post-921104