How is deflection modeled?
Question: How is deflection modeled and what reference axis it is measured from? Specifically: Is KMT based on the original axis (mine is FP & baseline) ?
Does the deflection affect where or how GMT is measured ?
Also, if LBP is set and deflection is zero at FP & AP, is "deflection overall" due to vessel extending beyond FP & AP ?
I tried to run GHS /KM and this caused a notation "deflection eliminated", is this normal operation?
Also, how is deflection modeled ? Is the hull shape changed, or the waterline changed to a "wave" of some kind.
My run with deflection caused an increase in VCB ? If the hull were deflected below the baseline, I would expect a decrease.
Basically, is the change in GMT above based on deflected hull or some shift ?
Your two GHS-command reports show different displacements; therefore, they are not representative of the same condition. This explains the difference in VCB. Here is a command sequence you can use: LBP fwdloc, aftloc VCG vcg DRAFT ... SOLVE WEIGHT, LCG, TCG GHS SOLVE GHS The second GHS command will be for the same weight and CG; only the deflection will not be present because the SOLVE command eliminated it. (Any command which changes the waterplane eliminates the deflection.) The reported deflection value can be based on the overall vessel end locations or the locations specified by the LPB or LWL command. In order to have it report deflection at the FP and AP locations, you must use the form of the LBP command which gives these locations, not just the LBP length. In answer your other questions: KMt is always measured from the baseline and perpendicular to it. But GHS does not compute KMt with deflection. The fundamental metacenter value is GM, not KM. (KM must be derived from GM.) GM is always perpendicular to the waterplane; i.e. a plane angled according to the present trim and heel. Deflection is actually modeled by curving the waterplane, not the vessel. Therefore, the axes remain straight; and a location such as the CG does not change its coordinate values when deflection is added. Therefore, GMt is measured from the same "G" with and without deflection.

Copyright (C) 2011 Creative Systems, Inc.