The highest hull stresses recorded on ocean going ships have come from the Great Lakes. The size of the lakes, and their orientation to the direction of typical storm wind directions along with wave reflections from the shore creates confused wave patterns, and the size of the lakes leads to waves that are of very short period with steep slopes.
I have sailed both the North Atlantic and the Great Lakes. The difference is that waves on the lakes are typically 4-6 seconds apart whereas on the Atlantic the periods run to 14-15 seconds. 25 foot waves at sea are ugly, and can cause problems, but they are slow and have a rhythm to them. On the other hand, 10 footers on the lakes come at you like a pack of wolves. They knock you around from every direction and are relentless, never giving you a break to collect your wits.
I've sailed in 40 knots in both places. At sea, it's a tiring nuisance, on the lakes it is simply terrifying. I have cooked dinner for the crew on the Atlantic. On Lake Ontario, all I could do was hang on and try to control the boat as everything down below became a tossed salad and the cockpit filled with water. The size of the lakes magnifies the problems in that the worst waves are at the ends of the lakes where you run out of room and wind up having to make very dangerous maneuvers or get blown up on the beach. The lack of sea room to leeward takes away the option of running ahead of the waves, an option which you often have at sea.
Ships are getting stronger, and weather forecasting is getting more accurate, and that is why the Edmund Fitzgerald will probably be the last really big ship to go down on the lakes, but they still claim their share of smaller boats, some of which are manned by professionals as witnessed by the loss of two Coast Guard crewmen several years ago on Lake Ontario not far from where I work. And the periodic loss of experienced sailors every summer due to surprise squalls or the late season storms.
