What causes a catastrophic capsize?

Too many factors to speculate, but icing of the topsides is usually at the top of the list for that type of incident in that location which is why they call it the deadliest catch. Of course, the usual answer is a perfect storm of otherwise minor events.

On a Deadliest Catch crab boat.....the 2 main contributors would be too much ice or too many traps stacked on deck, or a loss of pumps and slack crab tanks (free surface effect on stability).

I would say that tank management is the biggest culprit. A tank that was pressed that leaks, corroded piping, inoperable valves, wrong tanks selected to be filled or empty, etc.

If you watch the show the icing is scary as hell, but usually gets managed. I sure as hell would not want to be hammering that ice for 8+ hours with a baseball bat. But the most serious issues always seem to come down to tank management and tank leaks.

For those who still read books there is an excellent one that explains the loss of the Americus and Altair.

It is called Lost at Sea, An American Tragedy, by Patrick Dillon. ISBN 0-385-31421-3.