If you try to run a prediction for your multihull and get an error, you may want to consider these common sources of error:
- not selecting only half of the hull (and only up to the chine for planing hulls)
- incorrect model orientation (positive X should be in the aft direction, positive Z in the up direction)
- incorrect outward normal direction on the surface(s). When you select Direction in the Analyze menu, the arrows should point into the water.
- not positioning the centerline of the hull surface (even if it's a multihull) on the Y=0 plane
Also, we sometimes see that people have not set the units as they expect; you may want to go into Orca3D roperties, and in the Units section, be sure that the speed is set to knots and the power unit to HP.
If you feel that you need a prediction method that is specifically designed for multihulls, you may want to consider the NavCad software from HydroComp, Inc. (HydroComp supplies the resistance library that is used in Orca3D). You can read about NavCad at www.hydrocompinc.com. We'd also recommend reading the technical paper "Predicting Catamaran Resistance with NavCad" from HydroComp on multihull resistance prediction, at http://www.hydrocompinc.com/knowledge/whitepapers/HC105-NavCadCatResistance.pdf.