Hi,
I drew half of a hull LHT=13000 mm.
I want ORCA to give me the draft for a displacement of 12000 kgf.
With a WL parallel to the right z=0 (0 trim, as it comes on the Rhino drawing).
ORCA calculations give unrealistic results.
To obtain the draft should I use the “traditional method” (station areas, Simpson, etc.)?
Thanks for the help.
Michel
orca3d hydro.zip (1.7 MB)
The text and pics seem to me to indicate that you’re looking for a zero trim design waterline result.
Your second picture seems to indicate that you’re setting Orca up to solve for a free floating equilibrum given displacement and CG and the cg of 0,0,0 is producing an unexpected but quite possibly correct equilibrium.
Check the manual for how to produce hydrostatics tables. Most hydro software will let you produce tables for a series of displacements at a specified trim, forcing heel to zero and maintaining the specified trim.
Edit to add:
That question doesn’t appear to me to be related to the problem you’re having, which looks like asking for the wrong kind of solver: draft, heel, and trim equilibrium for a given load versus what you want, which is draft for a given displacement, trim (0), and I assume an implied heel also of 0.
If that’s the only answer you need, you could even solve for it in Rhino directly if you close your surface to make a solid. With the hydrostatics command and using volume plus waterplane area at each iteration and Newton-Raphson, you should pretty tight convergence within 3-5 iterations, either manually or with a script.
To compute the flotation with a weight and trim specified, you must use the Compute Hydrostatics & Stability function. This function allows you to specify the weight or the Sinkage, the LCG or the Trim, and the TCG or the Heel, in whatever combination you want. In your case, you want to specify the Weight (12000), Trim (0), and Heel (0) (don’t forget the Mirror checkbox if you only have half of the hull).
The Design Hydrostatics function which you were using doesn’t let you “mix and match” those quantities; it must either be Weight and CG, or Sinkage/Trim/Heel. And the real-time hydrostatics require Sinkage/Trim/Heel.
2 Likes