How do I analyze the volume of a part of a hull?

I want to design a catamaran hull. I know how to draw one. But I want to know the volume of the part below the waterline. It would be nice to do this without making the section under the waterline a separate solid. According to the help info for analyze mass properties I should be able to define a volume but I am not clear on how to do that. Attached is a file where I did a stupid example and made a box 12" on a side. Analyzing that volume gives a correct 1728 cubic inches result. I tried making a plane that cuts through the middle but that did not allow me to calculate only half the volume. I’m sure this should be a simple problem. Can someone point me in the right direction? play-cat.3dm (35.7 KB)

Create a box encasing all the hull from the waterline down and use CutVolume (select the hull first and the box second). That gives the volume of the intersection of the hull and the box (864 cu in for your example)


Thank you, Jeremy. How would a person know about the CutVolume command? I found it in the help files after you pointed me to it, but it appears nowhere in the toolbars or menus.

Have a look at the Hydrostatics command.

Hi Joe,

“I found it in the help files”. I guess you have answered your own question. Once I realised how little I knew about Rhino (it took several years) I took to looking there often. I also type commands speculatively more these days, rather than just picking from menus or toolbars, because Rhino responds with a list as I type and I see more things that don’t have UI links.


Thanks. I seem to have gotten the hydrostatics command to work. Sure wish I had had this years ago.

Hydrostatics command has been there for years!

That may be, but I’ve only had Rhino for about one year. I’ve been doing mostly ornamental ironwork designs this past year. Many years ago I did a design for a 25 foot monohull sailboat and still even have a planimeter for measuring areas. I had to do all the integration by calculator to find displacement. So now I have a little time to pursue my boating hobby and thought I’d try my hand at a catamaran. I am sometimes critical of Rhino mostly because of the limitations of the help files, especially in Grasshopper, but I continue to be amazed at what I can do with this program.
I felt very lucky to find Rhino. I had been looking for an affordable, useable 3D package for 2 or 3 years and was getting frustrated. Finally found Rhino by pure chance and was able to try it out before I bought. Great stuff.