This came up at dinner last night. Turns out my dear husband has read 3 books on this topic.

He said the ship did hit a shoal, but some time before its wreck, something like 4 hours before. They reported a 'bump' at the time.
(Not the exact words, of course.)

Later, in deep water, the Fitzgerald encountered a train of big waves whose wavelength was about that of the ship. When one wave crest lifted the bow, another lifted the stern, and the middle section, over a trough and weakened bt the earlier collision, gave way.

Experts studied that part of the lake and said that waves with a length like that were possible.

I have to agree with Kendall that if the ship had not been carrying extra weight, it might not have hit the shoal. Or it might have scraped more gently and the damage might have been less.

The DH thinks it was madness that they were on the lake at all.