How do I import hull geometry from Orca3D, PROLINES, or an STL file into NavCad?

Overview

Hull CAD Import automates extraction of NavCad hull form parameters from 3D geometry. This is the recommended approach for hull data entry it avoids the manual entry errors and estimation uncertainties that arise when parametric data is read off drawings. For planing hulls particularly, parameters like chine height, projected bottom area, and deadrise can be difficult to measure accurately from 2D documentation; CAD import derives them geometrically.

In NavCad 2025 and later, the Hull CAD Import module is presented as a docked page within the main NavCad interface for improved geometry viewing during the import process.

Supported Input Sources

• Orca3D / Rhino export the hull surface as a mesh (OBJ or compatible format) or use the direct Orca3D–NavCad workflow button within Rhino.
• PROLINES direct export of hull station data to NavCad format.
• STL files import one or more STL hull pieces, including multi-piece assemblies (hulland deck combined define ).

Import Procedure ITTC-78 (CT) Hulls

• Open Hull CAD Import from the menu: | Hull CAD Import.
• Load the geometry file and orient the hull to the NavCad coordinate system. Set the vessel's condition waterline using displacement and trim.
• Define station cut positions Standard, Fine, or Coarse using the station selector. ow and stern insets are recommended.
• Click Build to compute station intersections and extract hull form parameters.
• Review the extracted hull form data. Verify that computed parameters such as stern shape factor, half entrance angle, and section areas are physically reasonable.

Import Procedure Planing Hulls

For planing hulls, the procedure is similar but station cuts define the projected chine geometry. NavCad extracts projected bottom area, projected chine length, deadrise, and chine position at two reference stations. Chine points must be correctly identified during the intersection step for accurate planing geometry extraction.

Import Procedure STL Files Scripting

STL import supports multi-piece hulls using Overwrite (first piece) and Append (subsequent pieces) commands. This is particularly useful when scripting batch analyses across many hull variants. The startup script syntax is:

HullImport.Import [units] Overwrite "hull.stl"

HullImport.Import [units] Append "deck.stl"

HullImport.Orient [x] [y] [z] ' rotation angles to NavCad frame

HullImport.Scope ITTC78CT ' or Planing

HullImport.Stations Standard 0.5 0.5 %

HullImport.Build

For full scripting syntax details see the NavCad Scripting API help document.

After Import

Imported hull data can be manually adjusted if needed for example, to correct an effective transom area where the geometric area is zero due to a curved stern. Method Expert should be run after import to verify that the extracted parameters fall within valid ranges for the selected prediction method.

Related Articles

• How do I choose a resistance prediction method in NavCad?
• How does NavCad work with CFD tools like Orca3D Marine?
• How do I script a NavCad planing hull analysis (Savitsky) from an STL import?
• Savitsky method error low deadrise / planing station geometry troubleshooting