FreeShip layer characteristics

[LP]

When assigning mechanical properties, density and thickness, how is that mass distributed?

Is it centered about the surface? Or does it start at the surface and extend in the direction of the normals? Or opposite the normals?

[LP]

To respond to my own question , in the event that others might like to know, the mass appears to be centered about the centroid(?) of the part (layer) in question. It's the simplest solution, although, maybe not the best solution.

I had hoped that the CG would have been calculated with the thickness added opposite to the normals. While this sounds backwards, the normals define the exterior of the hull, so any thickness would be in the opposite direction.

[Martijn_vE]

LP,

The total area is calculated by calculating and adding the area and COG of each face. Thickness is not included. For zero thickness surfaces this is an exact solution, for surfaces with a small thickness the deviation can be neglected.

[PI Design]

Lp, Out of curiousity what are you trying to do that requires you to know? Centring the mass about the centoid must be fine for nearly all purposes, surely?

[LP]

I'm working on a design with full componentry. A comparison of the CG and CB indicated that they were not aligned so I defined some of the hull facets as ballast and gave them those properties. Just out of curiosity, I changed the properties to reflect those if water ballast was used. The resulting hydrostatic calculations gave me a lower CG with water than with lead. I had set the lead ballast thickness at 2" and the water ballast thickness at 12". I knew that the results were incorrect. I just needed to figure out why. I just figured that the thickness would be accounted for in the CG calculations.

I wasn't exact with converting between lead and water and ended up with slightly more water mass than lead mass. Thus, a lower overall (the whole vessel) CG was lower with the water.

Knowing how values are calculated will allow me to define masses more accurately. I'll just have to define cross-sections where thick sections are used(i.e. ballast, water tanks, fuel tanks, etc...).