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

(Requires GHS version 15.36B or later)

A weight item introduced by means of the ADD command can have a lateral plane area associated with it. This is useful for including small items in the wind area that contribute to the heeling moment without having to include them in the geometric model. The form of the ADD command that includes the LPA is,

ADD "description", weight, lcg ,tcg, vcg /LPA:area, lca, vca

If the center of the area is the same as the center of gravity, the area's center (lca, vca) can be omitted.

Here is an example:

Note that the BOOM command, being essentially a special form of the ADD command, also accepts the /LPA parameter. It locates the LPA together with the weight at the hookload sheave where the forces act on the vessel.

The center of pressure (LCP, HCP) is in reference to the waterplane. HCP especially is sensitive to the heel and trim angles as well as draft.

Weight items are independent of the 3D ship geometry model. They specify weight and center of gravity that may represent something in the geometry model, but there is no formal connection between an ADDed weight and the geometry. The LPA feature attaches a quasi-geometric structure to the weight item for the purpose of adding it to the lateral plane and wind area.

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