[Eric in the Ozarks]

The cargo hatch theory is one reason given for the list. Another possibility is that she "shoaled" scraped bottom on one of the numerous underwater mountains near Isle Royale. This is possible because the captain steered further north than usual to get some protection from the NE wind.
Another consideration is that the Fitz was pitching violently up and down and could have been pushed into the lake floor by a massive swell or wave. She was 729 feet long and now is in two pieces in about 550 feet of water. Its possible that her bow could have hit the bottom of the lake and snapped the boat in half.

[SolutionsOnly]

Most folks don't realize how deadly Lake Superior is.

There are a LOT of shipwwrecks on it.