This was a grounding, not striking a submerged office.
OMI the owner sued US government on grounds that the ship
whose draft was 33.75 ft grounded in an area where the charts say 35-36 ft.
Courts found in favor of government of grounds of sovereign immunity,
but neither side appears to have disputed the above fact.
link is http://www.cal.uscourts.gov/cgi-bin/getopn.pl?OPINION=02-1454.01A.
Real problem is pushing draft just as high as you can.