# Finding center of gravity of boat hull

I’d like to find the center of gravity of a boat hull. This requires the “solids”, the planking and frames to have attributes of weight or density. Is there something in Rhino that would help in this process? Any links to boar design groups?

You wanna make a preliminary calculation of the weight of the ship without modeling at least a little bit?

You’ll have to open the big o’textbooks (suggest Russian or Dutch ones) and calculate the volume by a coefficient depending on the structure type that’s inside. Suffice it to say, even that would require you to at least model volumes depending on the type of structure.

That is if you don’t want to pay for software, there are already propriatary Rhnio plugins for ship structure. Just search the web.

A new plugin that looks promising for this field.

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Based on another post the original poster made I believe his question is related to simple small boats, not ships, and he is interested in obtaining the weight and center of gravity location of a boat based on a Rhino model and the density of the materials.

Rhino by itself does not have the ability to assign material properties to parts. There is add-on software such as Orca3D (www.orca3d.com) which provides for assignment of material properties and subsequent calculation of weight, CG, etc.

It is possible to calculate the mass and CG of a boat using Rhino commands and a simple spreadsheet (or piece of paper). Mass properties of solid portions model can be calculated using the
The Rhino volume (mass) property commands, Volume, VolumeCentroid, and VolumeMoments calculate volume properties for closed surfaces (solids). These commands work for selections of multiple closed surfaces and report the cumulative properties. Use the commands for the parts of each material, record the results and multiply by the material density to obtain the mass properties of the those parts.

For thin parts such as those made from plywood or sheet metal models of the surfaces can be used and the surface properties calculated using Area, AreaCentroid and AreaMoments. This commands work for selections of multiple surfaces and report the cumulative properties. Use the commands for the parts of each material, record the results and multiply by the material density x part thickness to obtain the for the mass properties of the those parts.

Total mass can be obtained by simply adding the masses of the separate parts. Total center of gravity is a bit more complicated because a weighted average needs to be used. Multiply the centroid coordinates of each part (or set of parts) by the ratio of the mass of those parts to the total mass and then add the resulting scaled centroid locations for the total CG.

Total moments are more complicated but can be obtained in a similar manner…

Hmm, orca3d calculating weight, that doesn’t seem right.
Orca3d is for initial design, not for basic/detail etc. Weight there can only be an approximated one, as mentioned above using coefficients based on type of structure.

Orca3D is invaluable for calculating weight on a volume, area, or point weight basis. Quick example:
PUS 13.4 8-20 Weight And Cost Report.pdf (160.9 KB)

Orca3D is a plug-in for Rhino and it calculates weight using the Rhino model for the volumes, centroid locations, etc. Exact volumes, areas and lengths are calculate and used as needed. The user can define as many materials and their properties as needed. The user can also enter the weight and CG location for objects. Rhino also does cost estimates in the same manner using user entered cost properties.