The true cause of vessel instability?

A naval architect member of ITIC designed two vessels to be built to US Coastguard rules for work in the Gulf of Mexico. Shortly before the completion of the first vessel, the member advised ITIC that it had made an error the result of which was that the vessel would not meet the strict stability criteria.

As the delivery date was fast approaching, a solution to the problem was agreed between our member and the ship builders. This involved the fitting of two new bulkheads. However, shortly after the rectification work commenced, it transpired that there was nothing wrong with the original design. The cause of the apparent failure to meet the stability criteria was due to the use of different versions of software. The hull model was generated on a new version of the software, while the analysis was generated on an older edition. Rectification work ceased immediately and the vessel was restored with some minor modifications to the original design. The shipyard made a claim of USD 95,000 for the unnecessary work carried out. ITIC indemnified the member.