| The purpose
of the MAXVCG command is to produce curves of maximum VCG vs. displacement
based on a given stability criterion. The assumption behind this is
that all loadings which produce a given displacement and LCG have
the same maximum VCG as well as having zero TCG. Therefore, when free
surface is involved in a particular load, the VCG must be adjusted
for the free surface effect before comparing it with the maximum VCG.
The use of maximum VCG data should be restricted to loads where the
TCG is zero.
The MAXVCG command takes a series of weights and LCGs as inputs and
finds the corresponding maximum VCG for each combination of weight
and LCG, assuming that the TCG is zero. Alternatively it accepts drafts
and trims as inputs which it converts to weights and LCGs using the
intact waterplane at zero heel.
When trim, rather than LCG, is an input, the program must adjust the
LCG in concert with the VCG in order to maintain the given initial
trim. This requires additional steps and takes additional time.
Since the details of any particular loading are irrelevant during
the generation of maximum VCG curves, the present weight and tank
load settings are ignored during the process. The present fixed-weight
VCG, however, is taken as the "floor" value. If the MAXVCG
process finds that a maximum VCG is below the floor, it does not attempt
to find its value but merely reports that it is less than the floor
In addition to displaying a table and graph of the maximum VCG curves,
the MAXVCG command causes a "data base" of the maximum VCG
information is retained in memory. This data base is also saved on
a disk file by means of the SAVE command. Although the data held in
memory is lost when the GHS session ends, it may be restored by RUNning
the file which was written by the SAVE command.
This data base of maximum VCG data is accessible through two commands:
1) a special short form of the MAXVCG command; and
2) the LOAD EDIT command, which is available only when the Load Editor
module is included in the GHS installation.
When a particular condition has been defined (weights and tank loads)
and equilibrium has been found and the displacement, LCG and TCG are
within the limits required by the maxvcg data base, then the command
MAXVCG (without parameters) will access the data base and report the
maximum VCG which corresponds to the present condition.
The maximum VCG curves and the data base which result from a MAXVCG
command are based on certain factors which must be identically present
whenever the curves are applied. These factors include the stability
criterion, the heeling moment and the configuration of damage. When
any of these factors are changed, the data base becomes invalid and
can no longer be accessed.
It is possible to produce a composite data base consisting of the
lowest maximum VCG values from more than one execution of the MAXVCG
command. Details can be found in the MAXVCG command section of the
Command Dictionary or by typing HELP MAXVCG at the GHS prompt.
When damage is present (tanks with type = FLOODED) the MAXVCG command
keeps the tanks in the flooded state but it still assumes that the
TCG is zero. This means that the resulting maximum VCG data does not
apply to load conditions where the flooded tanks carry any load before
damage, since the loss of the load would change the condition.
When the assumptions inherent in the maximum VCG curves cannot be
satisfied, it is necessary to analyze each case of loading separately.
This can be done by beans of the SOLVE MAXVCG command. After setting
a load condition (weights and tank loads) the SOLVE MAXVCG command
will find the maximum value of the lightship VCG (or the VCG of a
particular added weight) which satisfies the present stability criterion.
There are no restrictions on the TCG or the tank loading prior to