General HydroStatics
Ship Stability Software
Command of the Week
(New or interesting aspects of GHS that you may not know about)

Tanks from Properties

GHS performs stability calculations by integrating the volumes described in the Geometry File. Free surfaces are modeled as shifts in the liquid center of gravity by default which naturally supports stability calculations at large angles of heel.

This is generally known to our readers, but what if you are working with a vessel that was built before computers (gasp) and there are no legible tank drawings? You might be surprised to learn that you can create a tank purely by entering tank property data and, in fact, these properties are stored as part of the shape definition in the Geometry File.

To do so, you'll need to create a Tank Property File containing volume, CG location and waterplane inertia data. See HELP MC_TPF for format.
With the command above, Model Converter imports tank properties from TANKPROP.TPF, stores the properties in the GF and even creates a simple 3D shape definition which matches the properties given. The 3D shape ensures that the tank functions correctly when the Geometry File is first read and all the tanks are TYPE INTACT. To force GHS to use the tank properties, simply change the tank to TYPE CALIBRATED.

The tank characteristics don't have to be derived solely from property tables. Anything that the properties don't address will be calculated in the normal way from the tank section data. This hybrid approach is useful if you have access to highly accurate tank volume data from direct metering. Although the strapping tables don't usually include adjustments for heel and trim, the measured volumes can account for structure inside the tank more accurately than a permeability factor. When in calibrated mode, the volume is interpolated from the properties, but the CG shifts are determined from the tank sections.

In this case, tank strapping tables need to be converted to a Tank Property File that Model Converter can read. An excerpt from a typical strapping table is shown below:

In order to convert a format like that to a two column table of height and volume, consider using the TPF Wizard.

Questions, comments, or requests?
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