

Question:

I'm getting deflection results from GHS that don't match those witnessed in
at the survey. The measured deflection at deadweight survey (based on 9
freeboard readings P/S) was 11.14 inches between the perpendiculars
(from 0 to 450 ft.). GHS calculates less than 3 inches.


Answer:

After your detailed WEIGHT command, put a DRAFT command using
your 9 P&S-averaged drafts, then a STATUS DELTA:

  WEIGHT ...
  DRAFT d1 @ l1, d2 @ l2, ... d9 @ l9
  STATUS DELTA

this will compare your measured displacement with the given weight. These should agree pretty closely. If not, something is wrong with the weight curve or the hull geometry or the draft readings. Any discrepancy there would have to be resolved first.

Then do the SMOD and LS commands. If the deflection out of LS still disagrees badly with the measurements, perhaps the SMOD needs to be refined and perhaps made a function of location. Also check that the Young's modulus is appropriate (see the LS command documentation).

Finally, it should be recognized that there may be limitations in beam theory (which GHS uses) being applied to the real hull so that exact correlation might be unattainable except by accident.