Why is margin line 76 cm below deck line ?

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line drawn parallel to, and not less than 3 inches below, the upper surface of bulkhead deck at the ship side; it defines the highest permissible location on the ship side of any damage waterplane in the final condition of sinkage, trim and heel

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  To maintain the vessel's remaining W/T integrity and condition of stability after flooding and for the safety of passenger it is necessary that no part of the bulkhead deck be submerged after flooding. The bulkhead deck is the uppermost continuous deck to which the Transverse watertight bulkheads are carried. If the bulkhead deck submerges, openings on the top of the bulkhead deck which are not watertight may submerge and lead to progressive flooding.
  To achieve this aim and for a margin of safety a margin line is drawn at least 76mm below the bulkhead deck. In any conditions of flooding this margin line is not to be submerged.

  Naveen Bijarania | 30-Jun-2013 11:13 | EDIT | REPLY