Watertight surface/mesh/solid to hull easiest possible

[ford3910@live.no]

Hi

I have autocad model of a boat. Its a “watertight” mesh.

What is the easies way to make this to a hull? Need to know metacentre of this hull,

[Peter Edmonds]

I can’t offer anything about importing an autocad mesh.

If you can get orthogonal views of the autocad shape you could use it as a background for the DELFTship model. You probably need not  be too fussy on fairing for a stability analysis.

The DELFTship model will allow you to  explore metacentric height readily over a range of displacements.

An alternative approach is based on very basic stability naval architecture:

• Strike a waterline on the autocad views.
• Measure cross sectional areas to this waterline.
• Integrate these longitudinally (Simpson’s rule or otherwise) to get volume of displacement.
• Obtain waterplane inertia I from either an equivalent rectangle (L B^3 /12) or by offsets and factors.
• Eyeball vertical centre of buoyancy B (not the breadth B)  from the cross sections.
• BM = I/V  ( V = volume of displacement ft^3, m^3)
• Determine vertical centre of gravity  G, and thus GM.

Only do this if you have some understanding in this area of naval architecture.

However I caution you against expecting to get anything meaningful from GM analysis for a boat. You may get something of value by comparison of a proposed design against a similar existing vessel of known but marginal stability.

For small commercial vessels GM on its own has long been abandoned as a  criterion for adequate stability. For current multi-factor stability criteria GM is  very rarely a make or break criterion. This comes from my preparation of stability particulars for many small commercial vessels over the years in the course of my professional practice in Australia, where we do small commercial vessel stability quite well.  (Reference – The National Standard for Commercial Vessels – Australian Maritime Safety Authority)

I expect a lot of this posting more properly belongs under Hydrostatics and Stability (?)

Peter Edmonds

Naval Architect

Perth  WA

 

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