There's a passage at page 74 that might explain what happened to Fitzgerald.
Getting pooped can be a scary experience. It happened to me in a Laser making an approach to the Dempster Street beach one afternoon, with a northerly building. In a Laser, if one is not expecting such a wave, as might be the case with an inland lake sailor, one goes swimming, and if one is unlucky, a pair of prescription sunglasses are somewhere at the bottom of the lake, but if one is prepared, there is a pair of prescription glasses in the car, and if one is lucky, there's a sailing buddy to give one a hug onshore.
It was around 6:30 in the evening. A short time later, two more gigantic waves boarded the [U.S. Steel iron boat Arthur] Anderson's decks. The first rolled over the ship's poop deck, the second hit the bridge deck, nearly 35 feet above the water. The Anderson stood up to them, but these waves would haunt [master Bernie] Cooper for years to come. By his calculations, if the heavy seas that hit his bridge deck continued down the lake, they would have hit the Fitz right about the time the ship disappeared."
I don't know, he said, but I've often wondered if those two seas might have been the ones. ..."
But a following sea big enough to bury an iron boat? What happened? The forensic evidence is inconclusive, and author Michael Schumacher leaves it to the reader to weigh the evidence and draw his or her own conclusion. Fitzgerald reported a broken fence rail, consistent with a hull failure caused by something called "hogging," wherein a ship rides the crests of waves at bow and stern in such a way as to subject the center of the hull to excessive flexing, and one of her last radio transmissions has the captain shouting that nobody is to go on deck (which would only be done in extremis under storm conditions.) Her track brought her quite close to Six Fathom Shoal, which subsequent surveys showed to be more extensive than the 1975 charts indicated, although dives on the shoals have turned up no evidence of contact with a hull. But she might have been low enough in the water to have been overwhelmed by those following seas.
As is often the case in a disaster, complacency is a contributing factor. Lake freighters are apparently stable enough that ocean-style edges are not required to keep the pencils and dividers on the chart tables. The relatively good safety record of the iron boats led to revisions of the winter waterline rules (buoyancy changes as water temperatures fall; the safe course is to require boats to ride higher in the water, but that means less cargo being transported.) Hatch clamps take time to dog down; perhaps it is better to secure a few, clear the ore dock, and begin the passage; there will be time to dog more of them down if the weather reports are unfavorable. But get-home-itis is the single biggest killer of truckers and aviators, and misguided notions of productivity are cofactors of get-home-itis in transportation generally. Some colleagues of Fitzgerald's master Ernest McSorley also offered less-than-favorable comments about his attitude toward routine maintenance. Take care of the O-rings and the space shuttle ...
Now if the editors at Bloomsbury had taken the time to remember that Detroit's J. L. Hudson Company used to do all sorts of publicity including decorating the accommodation of the country's biggest ore carrier and the old Thanksgiving Day parade, and that hatches have coamings. I was almost tempted to discredit the entire book for its repeated references, including in the glossary, to a "hatch combing." Landlubbers.