A group of three rogue waves, often called "three sisters", was reported in the vicinity of the Fitzgerald at the time she sank. The "three sisters" phenomenon is said to occur on Lake Superior as a result of a sequence of three rogue waves forming that are one-third larger than normal waves. When the first wave hits a ship's deck, before its water drains away the second wave strikes. The third incoming wave adds to the two accumulated backwashes suddenly overloading the deck with tons of water.
Captain Cooper of the Anderson reported that his ship was "hit by two 30 to 35 foot seas about 6:30 p.m., one burying the aft cabins and damaging a lifeboat by pushing it right down onto the saddle. The second wave of this size, perhaps 35 foot, came over the bridge deck." Cooper went on to say that these two waves, possibly followed by a third, continued in the direction of the Fitzgerald and would have struck about the time she sank. This theory postulates that the "three sisters" compounded the twin problems of the Fitzgerald's known list and her slower speed in heavy seas that already allowed water to remain on her deck for longer than usual.
The Edmund Fitzgerald episode of the 2010 television series Dive Detectives features the wave-generating tank of the Canadian National Research Council's Institute for Naval Technology and the tank's simulation of the effect of a 56 ft rogue wave upon a scale model of the Fitzgerald. The simulation indicated such a rogue wave could almost completely submerge the bow or stern of the ship with water, at least temporarily.
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