Hydrostatics works for wetted surface and floatation but not volume

I’ve created a model for a ship and I want to extract hydrostatics at various drafts. The model is all made of lofted surfaces, and it is mirrored so it’s the complete hull. I checked for naked edges on the mirrored model and the _ShowEdge command does not show any. The Hydrostatics command gives me wetted surface area, waterplane area, length, beam and centre of floatation and they appear OK. It does not calculate volume and centre of volume and I don’t understand why. How can it only work for some of the hydrostatics? The model’s base line is at z=0 on the global coordinate system. I’ve resorted to making solids out of the desired waterplane and the hull, and they work fine so I don’t understand why the hydrostatics won’t. Does it matter if there’s a closed “deck”? Should it be open on the upper side? Thanks in advance.

Hi -

In a simple test here, it works fine with both the upper side closed or open.
Please post your 3dm file for someone to take a closer look.

@Cd1 Your description corresponds to the results from Hydrostatics command if there is a naked edge below the waterline.

Are you trying to analyze a model of the outer hull surface only, or a model which includes hull thickness, and/or internal components and structure?

One side only or full model?

he model’s base line is at z=0 on the global coordinate system.
Are you setting WaterlineElevation greater than zero? The value is set in the world coordinate system, not a local Cplane system.
Hydrostatics | Rhino 3-D modeling

WaterLineElevation: The water plane must always be horizontal in world coordinates. (This is a limitation of the command, not a statement of a physical principle.) Its location is defined by specifying the depth of the origin in world coordinates.

Hi Wim, yes I did do this test with an open top and the results were the same. Unfortunately I’m not comfortable posting the model; I appreciate it all the same and I understand that any advice will be limited without being able to show what’s wrong.