I am working on a marine design project and exploring some historical discussions regarding RhinoMarine and Orca3D.
I would like to know: Without having the actual geometry or a complete offset matrix (such as exact hull widths and offsets at every half-meter interval), is it mathematically possible to accurately calculate or prove the exact coordinates of the Center of Buoyancy (X_B, Y_B, Z_B)?
If anyone has experience with hydrostatic calculations under limited data conditions in Rhino, please share your insights or recommended workflows.
What do you mean by “limited data conditions in Rhino”?
If you have the hull outer hull surface modeled in Rhino you have complete information about the hull shape. You can then use that information to calculate the center of buoyance using several different methods. You may need to extract the outer hull surface and assemble it into a single, watertight surface/polysurface, including filling any holes.
One method would be to use the Hydrostatics command which returns the center of buoyancy. To use Hydrostatics you need to provide the waterplane height which may require iteration. Hydrostatics | Rhino 3-D modeling
For inclined and/or trimmed conditions copy the hull surface surface/polysurface and rotate the copy to the desired orientation.
I have done stability analysis using the Hydrostatics command but it is tedious.
By “limited data,” I mean that I currently have the vessel’s overall dimensions and a preliminary design draft, but I do not yet have the complete watertight Rhino hull geometry or a verified lines/offsets plan.
I understand from your explanation that exact Center of Buoyancy coordinates can be calculated once the actual hull surface is properly modeled and made watertight, using Rhino’s Hydrostatics command.
For my current stage, I would therefore like to ask:
What would you consider the minimum reliable geometric information needed to build or reconstruct the hull in Rhino sufficiently for a meaningful hydrostatic/CB calculation?
For example, would station sections/sectional areas, waterline data, and a set of offsets be sufficient, or is a complete 3D hull surface required?
I am particularly interested in establishing a technically defensible workflow before treating any calculated CB coordinates as verified results.
So, for a preliminary estimate of the Center of Buoyancy, a sufficiently detailed set of stations, waterlines, or buttocks can be used with Simpson’s Rule, even without a complete 3D Rhino hull model.
For my understanding, would the required sectional data need to include the sectional areas and their centroid locations at each station in order to determine the longitudinal and vertical components of the CoB?
I am trying to distinguish between what is sufficient for a preliminary hydrostatic estimate and what would be required for a final, verified hydrostatic result.
For many hull types there are emperical “rules” for estimating displacement and center of buoyancy based on a limited set of dimensions. Some searching may be needed to find an appropriate “rule” for the hull type of interest. These rules are not related to Rhino
As @mc_rash said if you have station sections you can use Simpson’s rule. If the number of stations and/or station spacing do not work with Simpson’s rule you can use the trapezoidal rule or similar. That is how displacement, center of buoyancy and related were calculated before 3D models.
If you have the section shapes as curves then you can use the Area and AreaCentroid commands in Rhino to determine the curve areas and curve centroids. (There is also an AreaMoment command if needed). You’ll need to intersect the section shape curves with the waterplane to create closed curves of the below waterline shape.
I am working with Rhino on a confidential engineering application and would appreciate your guidance on a general technical question.
I need to determine hydrostatic properties from a valid closed 3D geometry, particularly:
submerged volume,
Center of Buoyancy (X, Y, Z),
waterplane-related hydrostatic data.
Could you please confirm the recommended Rhino workflow and the important modeling conditions required for a reliable Hydrostatics calculation?
I would also like to confirm whether the Center of Buoyancy obtained through Rhino Hydrostatics can be used as a CAD-based cross-check against a separate numerical integration method based on section data from the same validated geometry.
I am intentionally not providing any project-specific dimensions, geometry, application, architecture, calculations, or other confidential information. I only need general guidance regarding the Rhino methodology and required data conditions.
are you familiar with the science and engineering of floating structures like boats? Calculating the CoB is one of the most basic, and when knowing how to do it it’s one of the easiest, calculations in Naval Architecture.
I am not sure what you are really asking, what you have and what you want to achieve. There are several ways in determining/estimating/calculating the CoB, depending on what you have (e.g. curve of sectional areas, 3D model, …)
Use theHydrostatics command, which has been in Rhino since at least V4, or use the Orca3D plugin.
A surface/polysurfce of the submerged shape with no naked edges below the waterline. If the shape is symmetric then only one side is needed. (Naked edges on the plane of symmetry are okay.)
Yes if the Rhino shape matches the section data. To check if the Rhino shape matches the section data import the section data into Rhino as points or curves, and then compare that data to the surface. The results from the Hydrostatics command or Orca3D the Rhino shape will not exaclty match results from a separate numerical integration method based on section data from the same validated geometry because of differences in how the calcutions are done. Technically the results from Rhino should be more accurate.
If these calculations are critical for safety or regulatory approval you should consider engaging someone, such as a naval architect, with demonstrated expertise with these types of calculations to at least check your work.
Thank you again for your helpful guidance. Your explanation about matching the Rhino hull with the section data and validating the Hydrostatics results was very useful.
We’ll follow this approach and, if needed, have the calculations independently checked by an experienced naval architect.
I would like to request your assistance in creating a basic 3D CAD bounding-box model using the following dimensions:
Length: 210 m
Width: 32 m
Height: 26 m
Please create only the basic external construction envelope at this stage. No internal structures, mechanisms, systems, labels, or project-specific details are required.
Please keep the model clean, dimensionally accurate, and suitable for further CAD development. It’s urgent