GHS BULLETIN

GHS BULLETIN Downflooding Points (Applies to GHS, BHS, & BHS/YACHT version 6.20 and later)

The CRTPT Command

GHS maintains a list of "Critical Points" which are not associated with any particular part of the vessel model, but are used as points of downflooding and other purposes relating to the vessel as a whole. Critical points may be specified through Part Maker in the model-building stage. They may also be specified and changed with the main program.

A Critical Point consists of a name and a location (longitudinal, transverse and vertical coordinates). It also has two additional attributes: Symmetry status and Flooding status.

The Symmetry status of a Critical Point indicates whether the point is to be regarded as the single point represented by its coordinates (asymmetrical) or as actually two points, one symmetrically opposite the other (by negation of the transverse coordinate). By default the Symmetry status is asymmetrical. To make it symmetrical the following form of the CRTPT command is used (in the Main Program, not Part Maker):

    CRTPT ... /SYMMETRICAL

Any use of a critical point which implies only one point (eg. the HEIGHT command) uses only the point as given and ignores the Symmetry status.

The Flooding status has three states: Flooding, Tight and Noflooding.

Flooding means that the point will be regarded as a downflooding point as referenced by the FLD keyword in the LIMIT command and the DAMSTAB command.

Tight is similar to flooding but it applies only when the vessel is at the initial equilibrium angle. At other heel angles the Tight critical points are considered to be nonflooding.

Noflooding means that the critical point is ignored as a flooding point.

The Flooding status can be set in the main program by appending one of the parameters /FLOOD, /TIGHT or /NOFLOOD to the CRTPT command. The default is Flooding.

The FLDPT Command

The FLDPT command works in conjunction with the CRTPT command. It allows the Flooding status of any or all Critical Points to be conveniently changed. It has the following form:

    FLDPT [(n)] ON | OFF [/TIGHT]

n refers to one of the Critical Points. If it is absent, all Critical Points are implied.

ON turns on the Flooding status (Flooding or Tight, depending whether the /TIGHT parameter appears).

OFF sets the Flooding status to Nonflooding.

Effects of Flooding and Tight Critical Points

RA, MAXVCG and SOLVE MAX commands

The procedure invoked by these commands in turn refers to the stability criterion defined by LIMIT commands. When the FLD keyword is referenced by a LIMIT, it implies the downflooding points represented by Critical Points with Flooding status either Flooding or Tight. However, any Tight Critical Points are only considered when the vessel is in equilibrium.

CC Command

This command considers only Critical Points having Flooding status.

DAMSTAB Command

Like the RA command, DAMSTAB considers Critical Points having both Flooding and Tight status, but the Tight points are ignored except at the initial equilibrium.

DIVISION Command

The DIVISION command can reference a Critical Point when the /FLD parameter is used. For example,

    DIVISION ... /FLD: 2

associates Critical Point 2 with the division when it is being defined. It also sets the Critical Point to Flooding status in case it was not so designated before. When a Critical Point is associated with a division in this manner it prevents that point from being considered when that division is flooded during the DAMSTAB command process.

NOTE: MAXVCG, SOLVEMAX, DAMSTAB and DIVISION are not available in BHS.

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