GHS FAQ

Question QA008 :
How is the angle of equilibrium determined by the RA command when /FSM is used? For example, when HMMT is present and the equilibrium angle is not zero, how does the increased VCG due to the FSM adjustment affect the equilibrium angle ?

Answer :
The FSM adjustment is made by moving the CG upward perpendicular to the waterplane. Therefore it does not destroy equilibrium.
The only way to have RA /FSM start at equilibrium is to base the CG adjustment for FSM on the fully SOLVEd (equilibrium) condition (including tank CG shifts). This is done as follows:
 (set condition)
SOLVE
STATUS WEIGHT /FSM
RA /FSM
 If this is not what you want; i.e. if you want to use FSM rather than CG shifts in determining RA "equilibrium", you can fix the heel at, say, zero and do a partial solve:
 (set condition)
HEEL = 0
SOLVE TRIM
STATUS WEIGHT /FSM
RA /FSM
 In this case the RA curve will start at zero heel, not equilibrium; but you can reference EQU in your LIMIT commands.
Note that the STATUS WEIGHT /FSM command shows how the CG modification used by RA /FSM is based on the free surface moment.

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