Orca3D News

Tuesday, February 21, 2012

Trim Angle in Savitsky (planing) Analysis

We're sometimes asked whether the running trim angle that is reported in Orca3D's planing analysis is relative to the geometry as-drawn (i.e., as it is oriented in the Rhino coordinate system), or if it includes the effect of any static trim (that is, if the weight/CG that is used would result in an orientation different from how the boat is modeled).

The short answer to the question is that the reported trim angles are relative to the geometry as-drawn. Of course, if the boat is modeled such that the hydrostatic condition does not result in any trim relative to how the boat is modeled, there is no ambiguity. If there is significant static trim, it would be best to re-float the model using Orca3D's "Transform Model to Resultant Flotation Plane" option in the Hydrostatics dialog, so that the station shapes that are used in the Savitsky analysis are accurate representations of the vessel at rest.

But there is more to the answer, and it is well described in this post on HydroComp's blog (the Speed/Power library in Orca3D is licensed from HydroComp): http://navcadknowledge.wordpress.com/2008/11/04/savitsky-dynamic-trim/