A U.S. sailing report now says their boat was too unstable to sail in the competition.
The report includes a picture of the WingNuts one day after the accident in July, and it concludes that WingNuts' light-weight and unusual proportions made it vulnerable to capsizing in a race with the potential for extreme weather.
The 35-foot sailboat overturned during a fierce storm in the annual Chicago to Mackinac race.
Skipper Mark Morley and Suzanne Makowski-Bickel died.
Another vessel rescued the other six crew members.