# Stability question for autocad and delftship users

DELFTship forum Hydrostatics and stability Stability question for autocad and delftship users

• Author
Posts
• #38976
Žydrūnas
Participant

Hi. I’m trying to calculate stability for diferent heeling angles with free Delftship. I want to export hull as surface geometry (i get dxf file with polyface mesh in it) open it in AutoCad and then convert it to solid and trim it with waterline (waterline can be surface or another solid) to get center of buoyancy through properties. Hoewer, as usal, AutoCad doesn’t work as its supposed to. I cant convert it to solid. If i smooth surface, convert it to mesh and try to convert to solid it writes “mesh not converted because its not closed or self intersects”. Surface sculpt doesn’t work either. Any ideas how to get center of buoyancy for heeling angles?
Also, how delftship calculates initial metacentric height and how it determines Center of gravity?

• #38977
Robert Holme
Participant

After import of a Delftship DXF into Autocad I have the same issue. No-where have I been able to find a satisfactory explanation of this self intersecting.

By trial and error I have found that creating a NURBS surface in Autocad I can then use the thicken command to create a solid.

I work in imperial and an imported DXF is scaled at 1″ = 1ft. (I assume this is similar in metric) and needs to be scaled XYZ to world scale for subsequent operations.

HTH
Regards Maryak

• #38978
Icare
Participant

Hi Žydrūnas!

… it writes “mesh not converted because its not closed or self intersects”.

But you don’t tell us if you thought of closing the surface or not. :whistle:
Did you try to quickly draw a transom and a deck?
I assume AutoCAD needs the surface to be definitely closed before changing it in volume, otherwise there’ll be leaking points and the calculation will be impossible. (Note: Delftship has the tool to check the surface/leaking points).

I’m not 100% sure, but I guess you can check for the center of buoyancy with heeling angle using Delftship. I already mentioned this possibility (with a question mark) in a discussion bout lateral stability for asymmetrical hull: http://www.delftship.net/DELFTship/index.php/forum/hydrostatics-and-stability/3708-heeled-waterlines-and-calculating-righting-moment#4856 (Can a competent member of this forum tell me if I’m right?) .

The idea was to rotate the model 90° on a vertical axis, thus the lateral stability will be inverted with the longitudinal one. Then giving the model a pitch angle (which can be calculated) will be like giving it a heeling angle (which can’t be calculated… theoritically) and the longitudinal stability result will have to be considered as being the lateral stability result.

… I hope it’s clear… :unsure:

• #38980
Sharat Jami
Participant

Hello ICare,

Your Idea is nice where TCB becomes LCB & Vice versa, it will work,

DS is analysing only Longitudinal Stability in free version so you change Transverse stability to Longitudinal,…..also make sure you give frame of reference at amidships for a clearer understanding.