A ship has less room under it than people imagine.
Not fathoms of clear water, but a gap you could measure with a yardstick and still have some of the yardstick left over.
That gap is the entire margin.
A loaded bulk carrier drawing 38.5 feet in a channel dredged to 40 feet has about eighteen inches between its bottom plating and the riverbed.
The river is under no obligation to cooperate.
On the evening this one came upstream, the water was sitting almost two feet lower than the tide tables had promised it would be.
The clearance is not a safety margin
It is the operating condition.
A deep draft ship in a dredged river runs with almost nothing beneath it, and the channel edge is not a line on a chart but the start of a shoal.
Step outside and the depth changes fast.
The bottom beside this channel sits at about 35 feet, so a hull drawing 38.5 does not scrape it, it lands on it and stops being a moving object.
Speed makes it worse rather than better.
A hull moving quickly through shallow water squats and pulls itself down, which means the faster you go the less room you have, and nine knots is quick for that stretch.
The 623 feet and the 295 feet
The cargo was salt.
Solar salt loaded at Great Inagua in the Bahamas, roughly 45,000 tons of it, moving up the river toward a terminal above the city.
The lane it moves through is narrow.
Two hundred and ninety five feet of dredged width for a hull 623 feet long, with private docks reaching in to within 150 feet of the channel edge in places.
None of this happened out in open country.
The ship stopped less than half a mile above the bridge that carries traffic into the city, in the water off a residential neighborhood, with rowhouses in sight of the deck.
That geometry leaves nothing spare.
There is no shoulder to drift onto and no room to fix a mistake with a wide turn, only a lane with shallow water on both sides of it.
Fifteen minutes, twice
The first contact came at 6:14 in the evening.
The crew felt a jerk run through the hull while the ship was making around nine knots, and the master told the pilot they were outside the channel.
It did not end there.
Fourteen minutes later the ship grounded again and came to a dead stop, this time 140 feet outside the channel limits with 31 people aboard.
The tide was the quiet part.
Tables called for 3.6 feet of water over the reference level that evening and the gauge came in at 1.7, which took away more clearance than the ship had to start with.
Conditions were not extreme.
Northwest wind at 13 knots gusting to 22, air temperature at 27 degrees, and a flood current the tables put at 1.6 knots.
The current that was expected and never came
Everything turns on that current.
The pilot steered to starboard expecting the flood to set the ship back toward the middle, and the ship carried on to starboard instead.
Then it happened a second time.
After the first grounding, with the master already saying they were out of the channel, the same correction went in again, and investigators named the cause expectation bias.
The label is more useful than blame.
It describes acting on what the river was supposed to do rather than what it was doing, and the report puts bridge management at the center of the remedy.
Wheelhouses fail in recognizable ways.
A 443 foot freighter went onto rocks because a sleeping officer left nobody watching, which is the same category of failure arriving by a different road.
Three days on the bottom
The ship stayed where it stopped.
Bottom plating ruptured, water into four starboard ballast tanks and one empty fuel tank, no pollution reported and nobody aboard hurt.
It came off on the third day.
A rising tide lifted the hull clear, the ship was moved to a terminal upriver, and the damage was later put at 6.6 million dollars.
The river never actually closed.
A safety zone ran from the bridge up to that terminal, and traffic through it needed one hour of notice by radio rather than a shutdown.
Groundings get expensive in different currencies.
This one cost an owner money, while another grounding in Hawaii cost about 100,000 coral colonies and settled at roughly seven dollars an animal.
One detail sits underneath all of it.
The soundings behind the charts were ten months old on a riverbed that moves, which is a long time to trust a depth nobody can see.
Which brings it back to the yardstick.
A salt carrier that missed the lane by 140 feet was already running on eighteen inches, and the tide had taken the eighteen inches first.
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